Question 11 Mark
The resolving power of a telescope can be increased by increasing:
Answer
- Diameter of objective.
Explanation:
The resolving power of a telescope can be given as:
Resolving power $=\frac{1}{\text{d}(\theta)}=\frac{1}{1.22\lambda/ \text{D}}=\frac{\text{D}}{1.22}$ (wavelength)
So, resolving power can be increased by decreasing the wavelength and increasing the diameter of objective. View full question & answer→Question 21 Mark
Sound waves in air cannot be polarized because:
Answer
- These are longitudinal
Explanation:
Sound waves are longitudinal waves.
View full question & answer→Question 31 Mark
A wavefront is an imaginary surface where:
Answer
- Phase is same for all points.
Explanation:
The locus of all particles in a medium, vibrating in the same phase is called wave front.
The direction of propagation of light (ray of light) is perpendicular to the wave front.
A wave front is an imaginary surface where all particles lying on this vibrate in the same phase.
View full question & answer→Question 41 Mark
According to Maxwell , most of the optical properties of light depend on:
Answer
- Electric vector
Explanation:
The experiments on stationary light waves establish that most of the optical properties of light depends on the electric vector, which is also known as light vector.
View full question & answer→Question 51 Mark
To increase both the resolving power and magnifying power of a telescope:
Answer
- The wavelength of light has to be decreased.
Explanation:
Resolving power, $\text{R}=\frac{\text{a}}{1.22\lambda}$
where, a is diameter of objective $\lambda$ is wavelength of light magnifying power
$\text{m}=\frac{\text{-f}_0}{\text{f}_\text{e}}\Big(1+\frac{\text{f}_\text{e}}{\text{D}}\Big)$
so, decreasing the wavelength of light increases the resolving power and magnifying power of telescope. View full question & answer→Question 61 Mark
Figure shows a standard two slit arrangement with slits $S_1, S_2. P_1, P_2$ are the two minima points on either side of $P \ ($Fig$)$. At $P_2$ on the screen, there is a hole and behind $P_2$ is a second $2- $ slit arrangement with slits $S_3, S_4$ and a second screen behind them.
AnswerThere would be a regular two slit pattern on the second screen.Key concept:
Wave front,
Every point on the given wave front acts as a source of new disturbance called secondary wavelets which travel in all directions with the .velocity of light in the medium.
A surface touching these secondary wavelets tangentially in the forward direction at any instant gives the new wave front at that instant.
This is called secondary wave front.In the given question, there is a hole at point which is a maxima point.
From Huygen’s principle, wave will propagate from the sources $S_1$ and $S_2$.
Each point on the screen will act as secondary sources of wavelets.
The wave front emitted bu a narrow source is divided in two parts by reflection, refraction or diffraction.
The coherent soutces so obtained are imaginary.
View full question & answer→Question 71 Mark
Choose the correct option about light.
Answer
- Light does not require a material medium to propagate.
Explanation:
Light does not need medium to travel. Its an electromagnetic wave. All electromagnetic waves travel independent of medium.
View full question & answer→Question 81 Mark
Constructive and destructive interference occur in:
Answer
- All of these
Explanation:
Interference (constructive and destructive) is one of the basic properties of a wave, therefore it will occur in all the given waves, no matter they are electromagnetic or mechanical, transverse or longitudinal.
View full question & answer→Question 91 Mark
Huygens principle of secondary waves:
Answer
- Is a geometrical method to find, the position of a wave front.
Explanation:
Huygens's Principle states that every point on a wavefront is a source of secondary wavelets, which spread forward at the same speed.
Thus is enables to find the position of wavefront.
View full question & answer→Question 101 Mark
Evidence for the expanding universe is given by _______ of light spectrum received from them.
Answer
- Red shift
Explanation:
In physics red shift happens when light or other electromagnetic radiation from an object is increased to a wavelength or shifted to the red end of spectrum. A red shift occurs whenever a light source moves away from the observer.
A special instance of this in the cosmological red shift, which is due to the expansion of the universe, and sufficiently distant light source shows red shift corresponding to the rate of increase in their distance from earth.
View full question & answer→Question 111 Mark
In the set up shown, the two slits $S_1$ and $S_{2}$ are not equidistant from the slit S. The central fringe at $O$ is then:
AnswerAs the two slits $S_1$ and $S_2$ are not equidistant from the slit s the distance traversed by light through $S_1$ and $S_2$ may not differ by an integral multiple of wavelength. Thus it need not be bright . similarly it need not be dark.
View full question & answer→Question 121 Mark
For light diverging from a point source:
Answer
- The wavefront is spherical.
- The intensity decreases in proportion to the distance squared.
Solution:
| Type of wavefront |
Intensity |
Amplitude |
 |
$\text{I}\propto\frac{1}{\text{r}^2}$ |
$\text{A}\propto\frac{1}{\text{r}}$ |
 |
$\text{I}\propto\frac{1}{\text{r}}$ |
$\text{A}\propto\frac{1}{\sqrt{\text{r}}}$ |
 |
$\text{I}\propto\text{r}^0$ |
$\text{A}\propto\text{r}^0$ |
Due to the point source light propagates in all directions symmetrically and hence, wevefront will be spherical as shown in the diagram.
As intensity of the source will be,
$\text{I}\propto\frac{1}{\text{r}^2}$
where, r is radius of the wavefront at any time
Hence the intensity decreases in proportion to the distance squared. View full question & answer→Question 131 Mark
Who first proposed that light was wave-like in character?
Answer
- Huygens
Explanation:
In 1678, Dutch physcist, christian Huygens beived that light was made up of waves vibrating up and down perpendicular to the direction of the light travels, and therefore formulated a way of visualising wave propagation. This became known as Huygens Principe.
View full question & answer→Question 141 Mark
Two coherent sources of different intensities send waves which interfere. The ratio of maximum intensity to the minimum intensity is 25. The intensities of the sources are in the ratio:
Answer
- 9 : 4
Explanation:
Ratio of maximum intensity and minimum intensity is given by
$\frac{\text{I}_\text{max}}{\text{I}_\text{min}}=\frac{(\sqrt{\text{I}_1}+\sqrt{\text{I}_2})^2}{(\sqrt{\text{I}_1}-\sqrt{\text{I}_2})^2}=\frac{25}{1}$
$\Rightarrow\sqrt{\text{I}_1}=3 \ \text{and}\ \sqrt{\text{I}_2}=2$
$\Rightarrow\text{I}_1=9\ \text{and}\ \text{I}_2=4$
Then,
$\frac{\text{I}_1}{\text{I}_2}=\frac{9}{4}$ View full question & answer→Question 151 Mark
Newton postulated his corpuscular theory of light on the basis of:
Answer
- Rectilinear propagation of light.
Explanation:
According to Isaac Newton the geometric nature of reflection and refraction of light could only be explained if light was made of particles, referred to as corpuscles that travel in straight line.
View full question & answer→Question 161 Mark
A Young's double slit experiment is performed with white light:
Answer
- The central fringe will be white.
- There will not be a completely dark fringe.
- The fringe next to the central will be violet.
Explanation:
The superposition of all the colours at the central maxima gives the central band a white colour. As we go from the centre to corner, the fringe colour goes from violet to red. There will not be a completely dark fringe, as complete destructive interference does not take place.
View full question & answer→Question 171 Mark
Answer
- Selective absorption of one of the polarised component.
Explanation:
Dichromism is the selective absorption of one orthogonal polarization component of an incident beam over the other. this phenomenon is due to anisotropy of the material, with one polarization component experiencing preferential absorption.
View full question & answer→Question 181 Mark
1: Primary waves can travel in all directions in an ether
2: Secondary waves can travel only in backward in an ether
Answer
- 1 is true, 2 is false
Explanation:
Primary wave can travel in all directions in ether.
Secondary waves can travel in forward direction in ether
The wavefronts gradually spread in all the directions. So at every point, we have a wave coming out. The primary wavefront is formed and again from the primary wavefront, a secondary waveform is formed and so on. The disturbance does not last for a long time.
View full question & answer→Question 191 Mark
The inverse square law of intensity $\Big(\text{i.e., the intensity}\propto\frac{1}{\text{r}^2}\Big)$ is valid for a:
Answer
- Point source.
Explanation:
Intensity of a point source obeys the inverse square law.
Intensity of light at distance r from the point source is given by
$\text{I}=\frac{\text{S}}{(4\pi\text{r}^2)}$
Where S is the source strength. View full question & answer→Question 201 Mark
A plane wave front falls on a convex lens. The emergent wave front is:
Answer
- Spherical converging
Explanation:
A convex lens is thicker at the middle. When a light ray is incident parallel
to principle axis it is refracted towards the focal point. Similarly when a plane wave front is incident on a convex lens the light is refracted towards a point on the focal plane.
As the light is getting focused at a point it is converging and the emerging wave front is a spherical converging.
View full question & answer→Question 211 Mark
Huygens's concept of secondary wave:
Answer
- Is a geometrical method to a find a wavefront.
Explanation:
Huygens principle states that "Every point on a wave-front may be considered a source of secondary spherical wavelets which spread out in the forward direction at the speed of light. The new wave-front is the tangential surface to all of these secondary wavelets."
Thus it is geometrical method to find the wavefront.
View full question & answer→Question 221 Mark
Huygens' wave theory is used:
Answer
- To find the position of the wave front.
Explanation:
Huygen proposed a hypothesis for the geometrical construction of the position of a common wavefront at any instant during the propogation of waves in a medium.
View full question & answer→Question 231 Mark
Light transmitted by nicol prism is:
Answer
- Plane polarised
Explanation:
Nicol prism is a polariser in which the O-ray is eliminated by total internal reflection and the light transmitted through it, is E-ray which is completely plane polarised light.
View full question & answer→Question 241 Mark
Consider a ray of light incident from air onto a slab of glass (refractive index n) of width d, at an angle θ. The phase difference between the ray reflected by the top surface of the glass and the bottom surface is:
Answer
- $\frac{4\pi\text{d}}{\lambda}\Big(1-\frac{1}{\text{n}^2}\sin^2\theta\Big)^{\frac{1}{2}}+\pi$
Solution:
None of the option is correct
Consider the diagram, the ray (P) is incident at an angle $\theta$ and gets reflected in the direction P' and refracted in the direction P. Due to reflection from the glass medium, there is a phase change of $\pi$.
According to snell's law, we have $\text{n}=\frac{\sin\theta}{\sin\text{r}}$
$\Rightarrow\sin\text{r}=\frac{\sin\theta}{\text{n}}$
$\Rightarrow\ \cos\text{r}=\sqrt{1-\sin2\text{r}}$
$\Rightarrow\ \cos\text{r}=\sqrt{1-\frac{\sin^2\theta}{\text{n}^2}}$
The time taken to travel along OP" is given by
$\Delta\text{t}=\frac{\text{OP}''}{\text{v}}$
$=\frac{\frac{\text{d}}{\cos\text{r}}}{\frac{\text{c}}{\text{n}}}\ \Big[\because\ \text{PO}''=\frac{\text{d}}{\cos\text{r}}\text{ and }\text{v}=\frac{\text{c}}{\text{n}}\Big]$
$=\frac{\text{nd}}{\text{c}\cos\text{r}}$
$=\frac{\text{nd}}{\text{c}\Big(1-\frac{\sin^2\theta}{\text{n}^2}\Big)^{\frac{1}{2}}}\ \ \bigg[\because\ \cos\text{r}=\sqrt{1-\frac{\sin^2\theta}{\text{n}^2}}\bigg]$
$=\frac{\text{nTd}}{\lambda}\Big(1-\frac{\sin^2\theta}{\text{n}^2}\Big)^\frac{-1}{2}$
Now, the phase difference $(\Delta\phi)$ is given by
$\frac{2\pi}{\text{T}}\times\Delta\text{t}\times\frac{2\pi}{\text{T}}\times=\frac{\text{nTd}}{\lambda}\Big(1-\frac{\sin^2\theta}{\text{n}^2}\Big)^\frac{-1}{2}$
$=\frac{2\pi\text{nd}}{\lambda}\Big(1-\frac{\sin^2\theta}{\text{n}^2}\Big)^\frac{-1}{2}$
Therefore, the net phase difference $=\Delta\phi+\pi$
$=\frac{2\pi\text{nd}}{\lambda}\Big(1-\frac{\sin^2\theta}{\text{n}^2}\Big)^\frac{-1}{2}+\pi$ View full question & answer→Question 251 Mark
Polarisation of light establishes:
Answer
- Transverse nature of light
Explanation:
Polarisation of light establishes that light are transverse in nature, otherwise it was believed that they are longitudinal waves, like the sound waves.
View full question & answer→Question 261 Mark
A student is asked to measure the wavelength of monochromatic light. He sets up the apparatus as shown. $S_1,S_2,S_{3}$ are narrow parallel slits. $L$ is radiant lamps and $M$ is a micrometer eyepiece. The student fails to observe interference fringes. We would advice him to:
AnswerThe fringe width of a double slit interference pattern is given by
$\beta=\frac{\text{D}\lambda}{\text{d}}$
where $D$ is the distance between screen and the plane containing slits d is distance between the slits $S_2$ and $S_{3}.$
To make the fringe pattern visible, the fringe width must be increased, for which d should be decreased.
View full question & answer→Question 271 Mark
If the path difference between the slits $S_1$ and $S_2$ is $\lambda$, the central fringe will have an intensity of$:$
AnswerPath difference at the central fringe will be the same as the path difference at the slits i.e. $\lambda$.
Hence, the waves reaching the central fringe will be $180^\circ$ out of phase and will result in destructive interference.
Hence, the intensity of the central fringe will be $0.$
View full question & answer→Question 281 Mark
A person wishes to distinguish between two pillars located at a distance of 11km. What should be the minimum distance between these pillars (resolving power of normal human eye is 1')?
Answer
- 3.2m
Explanation:
Resolving power is given by the distance between two objects to be distinguished per unit distance of objects from the object distinguishing them.
Hence, $\theta=\frac{\text{d}}{\text{D}}$
Hence, $\theta\text{D}=\frac{1}{60}\times\frac{\pi}{180}\times110000$
= 3.2m View full question & answer→Question 291 Mark
The slits in a Young's double slit experiment have equal width and the source is placed symmetrically with respect to the slits. The intensity at the central fringe is $I_0.$ If one of the slits is closed, the intensity at this point will be$:$
AnswerTotal intensity coming from the source is $I_{0 }$ which is present at the central maxima. In case of two slits, the intensity is getting distributed between the two slits and for a single slit, the amplitude of light coming from the slit is reduced to half which leads to $\frac{1}{4}\text{th}$ of intensity.
View full question & answer→Question 301 Mark
Soap bubble looks coloured due to:
Answer
- Interference
Explanation:
Colours are seen due to interference between waves reflected from the top and bottom of soap bubble.
View full question & answer→Question 311 Mark
Albert Einstein used corpuscular theory to explain:
Answer
- The photoelectric effect
Explanation:
The photoelectric effect.
In 1905, Albert Einstein published a paper in advancing hypothesis that the light energy I'd being carried in discrete quantized packets to explain experimental data from photoelectric effect. This model contributed the development of quantum mechanics.
Photoelectric effect refers to the emission, or rejection of electrons grim the surface of generally a metal in response to the incident light.
View full question & answer→Question 321 Mark
The size of corpuscles are ________ for different colours.
Answer
- Different
Explanation:
The corpuscles can be of different sizes. The different colors of light are due to the different sizes of the corpuscles.
View full question & answer→Question 331 Mark
Which experiment seemed to make it clear that light propogates as a wave?
Answer
- Young's double-slit experiment
Explanation:
Young's double slit experiment
The double slit experiment is a demonstration that light and matter can display characteristics of both classically defined waves and particles. Moreover it displays the fundamentally probabislistic nature of quantum mechanical phenomena.
View full question & answer→Question 341 Mark
An electron microscope is superior to an optical microscope in terms of:
Answer
- Having better resolving power
Explanation:
The biggest advantage of an electron microscope over optical microscope is that they have a higher resolution and are therefore capable of a higher magnification ( up to 2 million times ).
However, optical microscopes show a useful magnification up to 1000−2000 times. This is a limit imposed by the wavelength of light. Electron microscopes, therefore, allow for the visualization of structures that would normally be not visible by optical microscopy.
View full question & answer→Question 351 Mark
Which of the following is wrong for interference fringes?
Answer
- Fringes are due to limited portion of wave front.
Explanation:
Statements B,C and D are correct whereas the statement "Fringes are due to limited portion of the wave front" is incorrect.
Interference fringes are formed due to the whole portion of wave front.
View full question & answer→Question 361 Mark
Wavefront of a wave has direction with wave motion:
Answer
- Perpendicular
Explanation:
Direction of wave is perpendicular to the wavefront.
View full question & answer→Question 371 Mark
Light travels in a ________ path:
Answer
- Rectilinear
Explanation:
Light travels in straight line unless it passes through a change in medium.
View full question & answer→Question 381 Mark
The resolving power of human eye is:
Answer
- ≈1′
Explanation:
As we know the visibility of the human eye is limited up to a distance.
It is known to us that the normal pupil size of any human being is 4mm. This measurement sets a minimum resolution approximately 1' to 2′.
When we want to pull small objects closer to our eyes, we aim to see them properly. But it is often seen that after crossing a certain distance the particles become unclear no matter how much closer it is to our eyes.
This signifies that there is a minimum distance of comfortable viewing. This distance is roughly calculated as 25cm.
View full question & answer→Question 391 Mark
By corpuscular theory of light, the phenomenon which can be explained is ____________.
Answer
- refraction
Explanation:
According to newton, when corpuscles approach the refracting surface, they are attracted near the surface. When they enter the denser medium from a rarer medium, their speed increases and hence change their direction.
View full question & answer→Question 401 Mark
The limit of resolution of eye is approximately:
Answer
- 1′
Explanation:
The resolution of the human eye is the smallest object our eye can see. This is limited by the diffraction limit, which is approximated by the angular size ratio of the object's size versus the distance to the object.
The normal pupil size of a human eye is 4mm, which sets a minimum angular resolution of the eye and to able to see the small objects we bring them as close to our eyes as possible, but there is a minimum distance for comfortable viewing which is roughly at 25cm.
But quoted figure for the smallest resolvable size is 0.1mm, showing that the diffraction limit is a crucial factor in visual resolving power.
View full question & answer→Question 411 Mark
The figure shows diffraction pattern of two nearby points. The two points are:
Answer
- Clearly resolved
Explanation:
Since there are a number of crests in between the peaks of the two points, they clearly do not immerse into each other at all, thus they are clearly resolved.
View full question & answer→Question 421 Mark
In Young's interference experiment, the central bright fringe can be identified due to the fact that it:
Answer
- Can be obtained by using white light instead of monochromatic light.
Explanation:
When we use white light, the central bright will have light from all wavelengths as none of them cancel out. Hence central bright fringe appears white.
For other bright fringes, depending on the wavelength of light constructive interference will not take place for certain wavelengths. Hence they will not be white, rather will be coloured, hence differentiated from central fringe.
View full question & answer→Question 431 Mark
Thin films like soap bubbles and oil floating on water can create colorful patterns. Which of the following explanations most accurately describes why this happens?
Answer
- Thin films provide reflection from the front and back surfaces, and this creates interference patterns.
Explanation:
The reason of colourful patterns on soap bubbles and oil on water is interference.
Infact, the reflected waves from upper and lower surfaces, get interference and produce colourful patterns.
View full question & answer→Question 441 Mark
Astronomers can tell whether a star is approaching or receding from the earth. Identify by which of the following method they can predict this?
Answer
- Doppler shift of the starlight
Explanation:
To predict the movement of a star, we compare the spectra of elements found in star (H, He Na etc.), first spectra which are obtained from star and second spectra from laboratory. If spectral lines of the spectra obtained from star, are shifting towards red end (called red shift) then star is going away from earth and if shifting is towards blue (called blue shift), then star is approaching the earth. This is Doppler's shift.
View full question & answer→Question 451 Mark
The equation of a light wave is written as $\text{y}=\text{A}\ \sin(\kappa\text{x}-\omega\text{t}).$ Here, y represents:
Answer
- Electric field.
Explanation:
Light consists of mutually perpendicular electric and magnetic fields. So, the equation of a light wave is represented by its field vector.
View full question & answer→Question 461 Mark
Which of the following statement is false:
Answer
- Sound wave exhibits polarization while light wave does not.
Explanation:
Polarization is a property of waves that can oscillate with more than one orientation. Electromagnetic waves such as light exhibit polarization, as do some other types of wave, such as gravitational waves.
Sound waves in a gas or liquid do not exhibit polarization, since the oscillation is always in the direction the wave travels.
View full question & answer→Question 471 Mark
A very thin film in reflected white light appears:
Answer
- black
Explanation:
For very thin films the distance travelled inside the film is insignificant and so the two reflected waves are almost exactly out of phase with each other (due to the phase change at one surface); they interfere destructively and the film appears 'black'.
View full question & answer→Question 481 Mark
Which of the following phenomenon can explain quantum nature of light:
Answer
- Photoelectric effect
Explanation:
Photoelectric effect explain the quantum nature of light while interference, diffraction and polarization explain the wave nature of light.
View full question & answer→Question 491 Mark
The angular spread of central maximum, in the diffraction pattern, does not depend on ______.
Answer
- The distance between the slit and sources
Explanation:
Angular spread of central maxima $=(\theta)=\frac{\lambda}{\text{b}}$
Where $\lambda$ = wavelength of light
b = width of slit
⇒ Clearly, it does depends on the distance between slit and sources. View full question & answer→Question 501 Mark
The radius of a wavefront as the waves propagate:
Answer
- Increases
Explanation:
As the waves propagates, it goes on creating secondary sources of light, resulting in increase in its radius.
View full question & answer→Question 511 Mark
Wave front formed by the collimator of a spectrometer:
Answer
- Spherical
Explanation:
Wave front formed by the collimator of a spectrometer is a plane wave front, when r lit is in the focus.
View full question & answer→Question 521 Mark
Antinodal curves correspond to _____ interference.
Answer
- Constructive
Explanation:
Antinodal curves correspond to constructive interference.
View full question & answer→Question 531 Mark
If light is passed through a double-slit opening and falls onto a screen, Identify the pattern produced on the screen.
Answer
- A bright central band of light with slightly diminished, alternating bright and dark bands.
Explanation:
When light is passed through a double slit opening, light from the two slits interfere at different points in the screen, forming alternating bright and dark fringes due to constructive and destructive interference respectively. However the intensities of higher order bands is slightly diminished.
Such an arrangement was first studied by Young, and has been since called Young's Double Slit Setup.
View full question & answer→Question 541 Mark
During the 19th century, light was considered to be a stream of particles called:
Answer
- Corpuscles
Explanation:
The corpuscular theory of light is proposed by newton in 1704. It is referred as particle theory or newton’s theory of light.
According to this theory,
Light is made up of tiny particles called corpuscles having negligible mass. These particles (corpuscles) are perfectly elastic.
These tiny particles always travel in straight line in all directions.
These corpuscles ravel at very high velocity.
These corpuscles are of different sizes. The different color of light is due to different sizes.
View full question & answer→Question 551 Mark
Suppose the medium in the previous question is water. Select the correct option$(s)$ from the list given in that question.
AnswerSince the speed of light is $a$ universal constant,
$\text{v}_\text{A}=\text{v}_\text{B}=\text{v}_\text{C}=3\times 10^8\text{m/s}$
$\text{v}_\text{B}=\frac{1}{2}(\text{u}_\text{A}+\text{u}_\text{C})$
This expression also implies that $v_A = v_B = v_C$
View full question & answer→Question 561 Mark
The transverse nature of light is shown by:
Answer
- Polarization of light
Explanation:
Polarisation of light establishes that light are transverse in nature, otherwise it was believed that they are longitudinal waves, like the sound waves.
View full question & answer→Question 571 Mark
Answer
- Both particle and wave phenomenon.
Explanation:
Light shows photoelectric effect and Compton effect, which depicts its particle nature. It also shows interference and diffraction, which depicts the wave nature of light.
View full question & answer→Question 581 Mark
The angular resolution of a telescope of $10\ cm$ diameter at a wavelength of $5000 \mathring{\text{A}}$ is of the order of:
Answer$\text{R}=\frac{1}{\Delta\theta}$
$=\frac{\text{a}}{1.22\lambda}$
$\frac{1}{\Delta\theta}=\frac{0.10}{1.22\times5000\times10^{-10}}$
$\Delta\theta=6.1\times10^{-6}\text{rad}$
View full question & answer→Question 591 Mark
If Young's double slit experiment is performed in water:
Answer
- The fringe width will decrease.
Explanation:
As fringe width is proportional to the wavelength and wavelength of light is inversely proportional to the refractive index of the medium,
Here,
$\lambda_\text{M}=\frac{\lambda}{\eta}$
$\lambda_\text{M}$ = wavelength in medium
$\lambda$ = wavelength in vacuum
$\eta$ = refractive index of medium
Hence, fringe width decreases when Young's double slit experiment is performed under water. View full question & answer→Question 601 Mark
If the source of light used in a Young's double slit experiment is changed from red to violet:
Answer
- Consecutive fringes will come closer.
Explanation:
Fringe width, $\beta=\frac{\lambda\text{D}}{\text{d}}$
Wavelength of red light is greater than wavelength of violet light; so, the fringe width will reduce. View full question & answer→Question 611 Mark
Consider sunlight incident on a slit of width $10^4A$. The image seen through the slit shall.
Answer
- Be a fine sharp slit white in colour at the center.
Solution:
Key concept:
Diffraction of Light is the phenomenon of bending of light around the comers of an obstacle/aperture of the size of the wavelength of light.
Size of the slit is very large compared to wavelength
Size of the slit is comparable to wavelenght
In figure $(A),$ no diffraction phenomenon is observed as the size of slit is weary large compared to wavelength. But in figure$(B),$ there will be diffraction of light as size of slit is compared to the wavelength of light incident.
Here in the question it is given, width of the slit
$\text{b}=10^4\mathring{\text{A}}=10^4\times10^{-10}\text{m}$
$=10^{-6}\text{m}=1\text{pm}$
Wavelength of (visible) sunlight varies from $4000\mathring{\text{A}}\text{ to }8000\mathring{\text{A}}$.
Hence the width of slit is comparable to that of wavelength, hence diffraction occurs with maxima at centre.
So, at the centre all colours appear,
i.e., mixing of colours form white patch at the centre. View full question & answer→Question 621 Mark
Which of the following properties show that light is a transverse wave?
Answer
- Polarization.
Explanation:
Reflection, interference and diffraction are the phenomena shown by both transverse waves and longitudinal waves. Polarization is the phenomenon shown only by transverse waves.
View full question & answer→Question 631 Mark
The wave theory of light, in its original form, was first postulated by.
Answer
- Christian Huygens
Explanation:
In 1678, Dutch physicist, Christian Huygens, believed that the light was made up of waves vibrating up and down perpendicular to the direction of the light travels and therefore formulated away of visualising wave propagation.
This becomes know as Huygens principle. Huygens theory was the successful theory of light in three dimensions. Huygens suggested that the light wave peaks form from surfaces like the layers of onion. In a vacuum or other uniform mediums the light waves are spherical and these wave surfaces advance or spread out as they travel at the speed if light.
This theory explains why light shining through a pinhole or slitwall spread out rather than going in straight lines.
View full question & answer→Question 641 Mark
When light is refracted, which of the following does not change?
Answer
- Frequency.
Explanation:
Frequency of a light wave doesnt change on changing the medium of propagation of light.
View full question & answer→Question 651 Mark
When a drop of oil is spread on a water surface, it displays beautiful colours in daylight because of:
Answer
- Interference of light.
Explanation:
Interference effect is produced by a thin film (coating of a thin layer of a translucent material on a medium of different refractive index which allows light to pass through it). ln the present case, oil floating on water forms a thin film on the surface of water, leading to the display of beautiful colours in daylight because of the interference of sunlight.
View full question & answer→Question 661 Mark
According to Newton, different colors of light are due to the difference in _______ of the corpuscles.
Answer
- size
Explanation:
Corpuscles are single, infinitesimally small, particles which have shape, size, color, and other physical properties.
View full question & answer→Question 671 Mark
Which of the following sources gives best monochromatic light?
Answer
- A laser.
Explanation:
Among the given sources, laser is the best coherent source providing monochromatic light with constant phase difference.
View full question & answer→Question 681 Mark
Light waves travel in vaccum along the y-axis. Then the wave front is:
Answer
- y = constant
Explanation:
waves front are plane perpendicular to the direction of rays.
so, as light is traveling along y - axis, plane perpendicular to y - axis is the x-z plane with any constant value of y.
so, y = constant is the wave front plane
View full question & answer→Question 691 Mark
In an astronomical microscope, the focal length of the objective is made:
Answer
- Greater than that of the eye piece
Explanation:
In an Astronomical telescope, the objective lens has a greater radius than the eyepiece.
Thus the objective lens has a greater focal length than the eyepiece.
View full question & answer→Question 701 Mark
The wavefronts of a light wave travelling in vacuum are given by $x + y + z = c.$ The angle made by the direction of propagation of light with the $X-$axis is$:$
AnswerOn writing the given equation in the plane equation form $lx + my + nz = p,$
Where $l^2 + m^2 + n^2$ and $p > 0,$ we get$:$
$\frac{1}{\sqrt{3}}\text{x}+\frac{1}{\sqrt{3}}\text{y}+\frac{1}{\sqrt{3}}\text{z}=\frac{\text{c}}{\sqrt{3}}$
If $\theta$ is the angle between the normal and $+x$ axis, then
$\cos\theta=\frac{1}{\sqrt{3}}$
$\Rightarrow\theta=\cos^{-1}\Big(\frac{1}{\sqrt{3}}\Big) $
View full question & answer→Question 711 Mark
The phenomenon of rotation of plane polarized light is called:
Answer
- Optical activity
Explanation:
The phenomenon of rotation of plane polarized light is called optical activity.
View full question & answer→Question 721 Mark
In which of the following the final image is erect?
Answer
- Simple microscope
Explanation:
The image formed by the Compound microscope and Astronomical telescope is inverted,but in case of Simple microscope it form erect image.
View full question & answer→Question 731 Mark
An observer on earth observes that wave length of spectral line in spectrum of a milky way shifts towards red end of spectrum. According to the observer, the milky-way is:
Answer
- Receding away from the earth
Explanation:
When an object moves away from us, its light waves are stretched into lower frequencies or longer wavelengths, and we say that the light is redshifted.
It also explain the expanding nature of universe. Shifting towards red end means wavelength is increasing. There, milkyway is receding away from earth.
View full question & answer→Question 741 Mark
A thin slice is cut out of a glass cylinder along a plane parallel to its axis. The slice is placed on a flat glass plae as shown in figure. The observed interference fringes from this combination shall be:
Answer
- Straight
Explanation:
The locus of the equal path difference consists in lines going parallel to the axis of cylinder.
Therefore, interference fringes will be straight.
View full question & answer→Question 751 Mark
What type of diffraction takes place in case of Young's double slit experiment?
Question 761 Mark
Using visible light what is the shortest wavelength which can be measured?
Question 771 Mark
Two identical lights sources $S_1$ and $S_2$ emit the light of same wavelength $\lambda$. These light rays will exhibit interference if:
AnswerFor interference to take place the light sources need to be either in phase or have a constant phase difference. In case the phase difference keeps changing the interference pattern will keep on changing, as a result of interference pattern will be observed.
View full question & answer→Question 781 Mark
When a drop of oil is spread on a water surface, it displays beautiful colors in daylight because of:
Answer
- Interference of light
Explanation:
When a drop of oil is spread on a water surface, it displays beautiful colors in daylight because the oil film is only a few nano-meters thick. Some of the light is reflected off the top surface and some the bottom surface. Because the thickness of the oil film is about the same as the wavelength of the light the two reflected rays interfere with each other.
View full question & answer→Question 791 Mark
If the apertature of a telescope is decreased the resolving power will:
Answer
- Decreases
Explanation:
Resolving power of a telescope $=\frac{\text{a}}{1.22\lambda}$
where a is the aperture of the telescope.
Thus resolving power∝ aperture.
Hence, if the aperture of telescope decreases, the resolving power decreases. View full question & answer→Question 801 Mark
In a Young's double slit experiment, the source is white light. One of the holes is covered by a red filter and another by a blue filter. In this case:
Answer
- There shall be no interference fringes.
Solution:
We know that, for the interference pattern to be formed on the screen, the sources should be coherent and emits lights of same frequency and wavelength.
In a Young's double-slit experiment, if one of the holes is covered by a red filter and another by a blue filter, then only red and blue lights are present due to alteration. In Young's double-slit experiment, a monochromatic light is used for the formation of fringes on the screen.
Therefore, there shall be no interference fringes.
View full question & answer→Question 811 Mark
Answer
- In vacuum.
- In a material medium.
Explanation:
Light is an electromagnetic wave that can travel through vacuum or any optical medium.
View full question & answer→Question 821 Mark
Two source $S_1$ and $S_2$ of intensity $I_1$ and $I_2$ are placed in front of a screen $[$Fig. (a)$]$. The patteren of intensity distribution seen in the central portion is given by Fig. $(b)$.
In this case which of the following statements are true. Answer
- $S_1$ and $S_2$ have the same intensities.
- $S_1$ and $S_2$ have a constant phase difference.
- $S_1$ and $S_2$ have the same wavelength.
Solution:
Key concept:
- For getting the sustained interference the initial phase difference between the interfering waves must remain constant, i.e., sources should be coherent.
For two coherent sources, the resultant intensity is given bt $\text{I}=\text{I}_1+\text{I}_2+2\sqrt{\text{I}_1\text{I}_2}\cos\phi$.
- Resultant intensity at the point of observation will be maximum.
$\text{I}_{\text{max}}=\text{I}_1+\text{I}_2+2\sqrt{\text{I}_1\text{I}_2}$
$\text{I}_\text{max}=(\sqrt{\text{I}_1}+\sqrt{\text{I}_2})^2$
- Resultant intensity at the point of observation will be minimum.
$\text{I}_{\text{max}}=\text{I}_1+\text{I}_2+2\sqrt{\text{I}_1\text{I}_2}$
$\text{I}_\text{max}=(\sqrt{\text{I}_1}+\sqrt{\text{I}_2})^2$ View full question & answer→Question 831 Mark
Answer
- All particles in it have same phase.
Explanation:
It is the imaginary surface representing corresponding points pf a wave that vibrate in unison. When identical waves having a common origin travel through a homogeneous medium, the corresponding crests and troughs at any instant phase.
View full question & answer→Question 841 Mark
Huygen's wave theory allows us to know:
Answer
- The propagation of the wave front.
Explanation:
Huygen's wave theory explain the propagation of the wave front.
View full question & answer→Question 851 Mark
In Young's interference experiment, if the slits are of unequal width, then:
Answer
- The positions of minimum intensity will not be completely dark.
Explanation:
Unequal width of slits will cause unequal intensity of lights entering from both slits.
As a result, during interference complete cancelling of light intensity will not take place at regions of otherwise dark fringe.
As the value of $\beta$ does not depend on intensity of light, there will be no shifting of fringes as well as no change in fringe width. View full question & answer→Question 861 Mark
Light waves can be polarised because they:
Answer
- Are transverse
Explanation:
Polarisation of light waves is possible only because they can oscillate in more than one orientation i.e., they are transverse in nature. It has no dependence on its wavelength and frequencies.
View full question & answer→Question 871 Mark
When light is refracted into a medium:
Answer
- Its wavelength decreases but frequency remains unchanged.
Explanation:
Frequency of a light wave, as it travels from one medium to another, always remains unchanged, while wavelength decreases.
Decrease in the wavelength of light entering a medium of refractive index $\mu$, is given by,
$\lambda_\text{M}=\frac{\lambda}{\mu},$
Where $\lambda_\text{M}$ = wavelength in medium
$\lambda$ = wavelength in vacuum
$\mu$ = refractive index View full question & answer→Question 881 Mark
A person shines a coherent light of a bulb through an object, A, which produces a pattern of concentric rings on a screen, B. A is most likely:
Answer
- A sheet with a pinhole
Explanation:
A polarization filter will limit the light vectors in a single plane i.e. polarization.
A prism will split the light i.e. dispersion .
A slit system will make a diffraction pattern on screen B, but in this pattern, fringes are straight.
Due to its circular size, a pinhole will produce diffraction pattern on screen B in the forms of concentric rings.
View full question & answer→Question 891 Mark
Light waves exhibit polarization but sound waves do not exhibit polarization because they are not:
Answer
- Transverse
Explanation:
Only transverse waves can exhibit polarization.
Light waves are transverse waves whereas sound waves are longitudinal waves, hence sound waves can not be polarized.
View full question & answer→Question 901 Mark
The shape of wave front at a very large distance from source is ______.
Answer
- Plane
Explanation:
Due to the large distance, the radius of the wavefront can be considered as large (infinity) and hence, a wavefront is almost plane.
View full question & answer→Question 911 Mark
A white light is passed through the two narrow slits and produced a pattern of alternating bright and dark lines on the screen as shown above. What will effects on the central bright band , if the distance between screen and slits are increased?
Answer
- Become wider
Explanation:
The setup shown is that of Young's Double Slit Experiment.
The fringe width in the experiment is given as $\beta=\frac{\text{D}\lambda}{\text{d}}$
where d is the distance between the slits, D is the distance between screen and slits.
Hence the central fringe also widens when distance between screen and slits increases. View full question & answer→Question 921 Mark
A microscope is used with sodium light and its resolving power is not sufficiently large. Higher resolution will be obtained by using wavelength of:
Answer
- 400$\mathring{\text{A}}$
Explanation:
Since power of resolution is more for violet than for red, we conclude that resolving power is greater for light with lower wavelengths.
Wavelength of sodium light is around 589nm.
Hence resolving power increases for light with lower wavelength. View full question & answer→Question 931 Mark
Two nearby objects are just resolved, if the principle maximum in the diffraction pattern of one coincides with:
Answer
- First minimum of the other
Explanation:
The Rayleigh criterion is the generally accepted criterion for the minimum resolvable detail - the imaging process is said to be diffraction-limited when the first diffraction minimum of the image of one source point coincides with the maximum of another.
View full question & answer→Question 941 Mark
The magnitude of magnifying power of an astronomical telescope is $5,$ the focal power of its eyepiece is $10$ diopters. The focal power of its objective $($in diopters$)$ is$:$
Answer$M = 5$
$P_e= 10$
$\frac{1}{\text{f}_\text{e}}=10$
$f_e = \frac{1}{10},m = 10\ cm$
$M = \frac{\text{f}_\text{0}}{\text{f}_\text{e}} =5$
$f_{0 }= 50\ cm$
$P = 2D$
View full question & answer→Question 951 Mark
A thin transparent sheet is placed in front of a Young's double slit. The fringe-width will:
Answer
- Remain same.
Explanation:
On the introduction of a transparent sheet in front of one of the slits, the fringe pattern will shift slightly but the width will remain the same.
View full question & answer→Question 961 Mark
Which of the following is correct for light diverging from a point source?
Answer
- The intensity decreases in proportion for the distance squared.
Explanation:
A point source produces a spherical wavefront that moves in all the directions from the point.
Whereas the intensity at the wavelength is dependent on the distance and it follows the inverse square law. So, the intensity decreases with an increase in the distance from the source.
View full question & answer→Question 971 Mark
In YDSE, the slit widths are in the ratio of 1:9. The ratio of intensity of the maxima to that of the minima is:
Answer
- 4:1
Explanation:
Intensity is proportional to the area of the slit.
As slit widths are in the ratio of 1:9
The areas are also in the ratio 1:9
Thus Intensities are in the ratio 1:9
amplitudes are square root of Intensities
Thus amplitudes are in ratio 1:3
Let amplitudes be x and 3x
At maxima the amplitudes get added up x + 3x = 4x
At minima they become x − 3x = −2x
Intensity of maxima to minima is $\frac{16\text{x}^2}{4\text{x}^2}=\frac{4}{1}$ View full question & answer→Question 981 Mark
In optical instruments, the lenses are used to form images by:
Answer
- Refraction
Explanation:
In optical instruments, the lenses are used to form images by Refraction.
View full question & answer→Question 991 Mark
The interfering fringes formed by a thin oil film on water are seen in yellow light of sodium lamp. We find the fringes:
Answer
- Yellow and black
Explanation:
When the yellow light of sodium lamp interferes constructively we get yellow bright band, and when they interfere destructively we get black bark band.
View full question & answer→Question 1001 Mark
The speed at which the current travels in a conductor, is nearly.
AnswerThe speed of the current in the conductor is the same as the speed of light in the vacuum which is $3\times 10^8\frac{\text{m}}{\text{s}}$
View full question & answer→Question 1011 Mark
Anti-nodal curves represent the points joining:
Answer
- Constructive interference
Explanation:
Conceptual, anti node represents joining of all points in constructive interface as the amplitude is high.
View full question & answer→Question 1021 Mark
If a star emitting yellow light is accelerated towards earth, then to an observer on earth it will appear?
Answer
- Gradually changing to blue
Explanation:
As the star coming closer to the earth, the frequency of the light increase and the wavelength decrease due to doppler effect. So the colour should gradually change to blue.
View full question & answer→Question 1031 Mark
Making a light wave vibrate in only one plane is known as:
Answer
- Polarization.
Explanation:
Light in the form of a plane wave in space is said to be linearly polarized. Light is a transverse electromagnetic wave, but natural light is generally unpolarized, all planes of propagation being equally probable.
The process of making the light wave vibrated in a single plane is known as polarization.
View full question & answer→Question 1041 Mark
Huygen's concept of wavelets is useful in:
Answer
- Geometrical reconstruction of a wavefront
Explanation:
Huygens considered that light was propagated in longitudinal waves.
Huygen's concept explained the direction of propagation of light waves by geometrical reconstruction of wavefront.
View full question & answer→Question 1051 Mark
When light falls on matter, it can produce:
Answer
- All the above
Explanation:
since photons have momentum and energy, they can produce all the three stated effects.
View full question & answer→Question 1061 Mark
Who amongst the following used corpuscular theory to explain the nature of light?
Answer
- Newton
Explanation:
Newton was the first to use corpuscular theory to explain the nature of light. He was able to successfully reflection and refraction using this theory.
View full question & answer→Question 1071 Mark
In Young's double slit experiment, the interference pattern obtained with white light will be:
Answer
- The central fringe achromatic and coloured fringes for small path difference.
Explanation:
If white light is used a white centre fringe is observed, but all the other fringes have coloured edges, the blue edge being nearer the centre. Eventually the fringes overlap and a uniform white light is produced.
View full question & answer→Question 1081 Mark
Which one of the following is more monocromatic?
Answer
- Laser beam
Explanation:
Monochromatic light is light made up of one single pure frequency.white light, which is light that contains all frequencies, That means the sum of red, yellow, green, blue and violet. Some light sources send out monochromatic light such as lasers beam.
View full question & answer→Question 1091 Mark
The ability of an optical instruments to show the images of two adjacent point objects as separate is called:
Answer
- Resolving power
Explanation:
By definition, resolving power of an optical instrument is its ability to show two closely adjacent point (closely spaced) as distinct as possible.
View full question & answer→Question 1101 Mark
Two sources are called coherent if they produce waves:
Answer
- Having a constant phase difference.
Explanation:
For light waves emitted by two sources of light to remain coherent, the initial phase difference between waves should remain constant in time. If the phase difference changes continuously or randomly with time, then the sources are incoherent.
View full question & answer→Question 1111 Mark
Which of the following properties shows that light is a transverse wave?
Answer
- Polarization
Explanation:
The polarization phenomenon, verifies the transverse nature of light. Since sound has longitudinal nature, so it does not show polarization effect.
View full question & answer→Question 1121 Mark
Identify which of the following should be used for polarised light waves?
I. Sunglasses
II. Remove ultraviolet light
III. Reveal stress patterns
Answer
- I and III only
Explanation:
Polarizers are used in industry to reveal stress patterns in machinery and tools. Sunglasses are used to protect the eyes by polarizing the light to reduce glare using the tailor-made material of the glasses.
View full question & answer→Question 1131 Mark
The amplitude modulated (AM) radio wave bends appreciably round the corners of a 1m × 1m board but the frequency modulated (FM) wave only negligibly bends. If the average wavelengths of AM and FM waves are $\lambda_\text{a}$ and $\lambda_\text{f}:$
Answer
- $\lambda_\text{a}>\lambda_\text{f}$
Explanation:
An electromagnetic wave bends round the corners of an obstacle if the size of the obstacle is comparable to the wavelength of the wave. An AM wave has less frequency than an FM wave, So, an AM wave has a higher wavelength than an FM wave and it bends round the comers of a 1m × 1m board. View full question & answer→Question 1141 Mark
Light waves travel in vacuum along the X-axis. Which of the following may represent the wavefronts?
Answer
- x = c.
Explanation:
The wave is travelling along the X-axis. So, it'll have planar wavefront perpendicular to the X-axis.
View full question & answer→Question 1151 Mark
All particles of a wave front vibrate:
Answer
- In same phase
Explanation:
Wave front by definition is the locus of points having same phase.
View full question & answer→Question 1161 Mark
In white light interference, nearest to the central (bright) fringe, will have which of the following colour:
Question 1171 Mark
The diameter of objective of a telescope is $1m.$ Its resolving limit for the light of wavelength $4538\mathring{\text{A}}$, will be$:$
AnswerResolving limit
$\text{d}\theta=\frac{1.22\lambda}{\text{a}}$
$=\frac{1.22\times4538\times10^{-10}}{1}$
$= 5.54\times 10^{−7}rad.$
View full question & answer→Question 1181 Mark
A man wishing to get a picture of a Zebra photographed a white donkey after fitting a glass with black streaks onto the objective of his camera.
Answer
- The image will look like a Zebra on the photograph.
Explanation:
The rays coming from the body of the white donkey will interfere with the black streaks on the glass and the final image of a zebra will be produced.
View full question & answer→Question 1191 Mark
Doppler's effect is sound in addition of relative velocity between source and observer, also depends while source and observer or both are moving. Doppler's effect in light depend only on the relative velocity of source and observer. The reason of this is.
Answer
- None of the above
Explanation:
Doppler effect refers to the change in wave frequency during the relative motion between a wave source and it's observer by considering that the Velocity of the observer with respect to the source velocity is negligible.
View full question & answer→Question 1201 Mark
Find out correct option which describe the Red shift of distant galaxies.
Answer
- Expansion of the universe
Explanation:
Red shift is the increase in wavelength of light observed due to Doppler Effect of light, observed when objects recede from each other.
The red shift as observed in distant galaxies suggests that the galaxies are moving away from us and from each other. This tells that the universe is expanding.
View full question & answer→Question 1211 Mark
The air film in a Newton's ring apparatus is replaced by an oil film. The radii of the rings:
Answer
- Decreases
Explanation:
Radius of nth order Newton's ring is proportional to $\sqrt{\lambda}$ which decreases in oil since $\lambda=\frac{\lambda_\text{vacuum}}{\mu}$. Thus the radius of newton's ring decreases in oil film. View full question & answer→Question 1221 Mark
The wave front due to a source situated at infinity is:
Answer
- Planar
Explanation:
when you considered it a large distance and measuring justice Mall section of it then it can be considered to be plane wavefront source at Infinity example the one coming from sun to earth surface is considered to be plain VU friend from light diverging from a point source will be spherical.
So, the wave front due to a source situated at infinity is planar.
View full question & answer→Question 1231 Mark
Answer
- Polarisation by double refraction
Explanation:
In 1669, another Danish scientist, Erasmus Bartholinus discovered the polarization of light by double refraction in Iceland spar (calcite).
View full question & answer→Question 1241 Mark
Which of the following statements about the behaviour of light is not correct?
Answer
- Interference patterns are evident for light behaving as rays.
Explanation:
Interference patterns are explained using wave nature of light. You can learn more from youtube video "Interference of light".
View full question & answer→Question 1251 Mark
The wavefronts of light coming from a distant source of unknown shape are nearly:
Answer
- Plane.
Explanation:
Wave travelling from a distant source always has plane wavefront.
View full question & answer→Question 1261 Mark
The resolving power of a telescope depends on:
Answer
- Diameter of the objective
Explanation:
Resolving power of telescope $\text{R}=\frac{1}{\Delta\theta}=\frac{\text{a}}{1.22\lambda}$
where, $\Delta\theta$ is angular separation between two objects.
a is the diameter of the objective.
$\lambda$ is wavelength of light.
So, clearly resolving power of a telescope depends on diameter of the objective. View full question & answer→Question 1271 Mark
When the light source is moving away, the Doppler effect for light is known as:
Answer
- Red Shift
Explanation:
When the wavelength of the light gets lengthened by the Doppler shift, we refer to the change as red shift.
View full question & answer→Question 1281 Mark
The wavefront is a surface in which:
Answer
- All points are in the same phase.
Explanation:
A wavefront is the locus of points characterized by propagation of position of the same phase:
a propagation of a line in 1D, a curve in 2D or a surface for a wave in 3D.
View full question & answer→Question 1291 Mark
Consider a light beam incident from air to a glass slab at Brewster's angle as shown in Fig. A polaroid is placed in the path of the emergent ray at point P and rotated about an axis passing through the centre and perpendicular to the plane of the polaroid.
Answer
- The intensity of light as seen through the Polaroid shall go through a minimum but not zero for two orientations of the polaroid.
Solution:
Hint: If a light beam incidents at Brewster's angle, then the transmitted beam is always unpolarised and reflected beam is always polarised.
In the given diagram, the light beam incident from air to the glass slab at Brewster's angle (ip)
. Therefore, the incident ray represented by dot (.), is unpolarised and the reflected light represented by arrow, is plane polarized.
Since, the emergent ray is unpolarised.
Hence, the intensity cannot be zero when passes through polaroid.
View full question & answer→Question 1301 Mark
In Young's double slit experiment the intensity of the maxima is $I.$ If the width of each slit is doubled, the intensity of the maxima will be$:$
Answer$I = I_{max} = 4I_{0}$
Now, $I0$ is increased to $2I0$
So, $I_{max }= 4(2I_0) = 8I_0 = 2I$
So, maximum intensity is $2I$
View full question & answer→Question 1311 Mark
For the propagation of light wave, medium is required. This is according to:
Answer
- Huygen's theory
Explanation:
Huygens suggested that light may be a wave phenomenon produced by mechanical vibrations of an all pervading hypothetical homogenous medium called eather just like those in solids and liguid .This medium was supposed to be mass less with extremely high elasticity and very low density.
View full question & answer→Question 1321 Mark
The parallel rays of white light are made an incident normally on an air film of uniform thickness. 250 fringes are seen in the transmitted light between 4000$\mathring{\text{A}}$ and 6500$\mathring{\text{A}}$. Thickness of air film is:
Answer
- 1.3mm
Explanation:
For a fringe to appear, the two wavelengths must interfere to give a maxima, which appears at a distance where the phase of both the rays are same, that is, at the least count multiple of the waves.
Therefore the first fringe appears at 5200$\mathring{\text{A}}$.
To accommodate 250 fringes, the thickness of the film is 250 times the distance where the first fringe occurs.
Thus the thickness of the air film is 1.3mm View full question & answer→Question 1331 Mark
The thinnest bubble film in air that can possibly strongly reflect red light because of constructive interference makes up a certain bubble. How could we create the thinnest bubble film that will strongly reflect purple light?
Answer
- Use a thicker film than the film used for the "red" bubble.
Explanation:
As to obtain a nice coloured pattern, the thickness of the film has to be similar to the wavelength of light and the bubbles are darkest where they are thinnest.
View full question & answer→Question 1341 Mark
Which of the following phenomena can be demonstrated by light. But not with sound waves in an air column?
Answer
- Polarization
Explanation:
As we know the reflection, refraction, diffraction can be demonstrated with sound waves in an air column but to have polarized waves, they first need to be transverse waves but sound waves are longitudinal. Sound waves are longitudinal so they cannot be polarised.
View full question & answer→Question 1351 Mark
Resolving power of a telescope increases with:
Answer
- Increase in aperture of objective
Explanation:
Resolving power of a telescope:
$\text{R}=\frac{\text{a}}{1.22\lambda}$
where, a is diameter of the objective
so, R increases when a is increased and a increases when aperture of objective is increased. View full question & answer→Question 1361 Mark
The wave theory in its original form was first postulated by:
Answer
- Christian Huygens
Explanation:
Christian Huygens postulated wave theory.
View full question & answer→Question 1371 Mark
Light travels faster in air than that in glass. This is accordance with:
Answer
- Wave theory of light
Explanation:
Huygene's wave theory assumed that the light travels slower in glass than in air. That means for a given geometrical distance in glass, there will be more waves of light than in same distance in air. Consequently, it would seem that wavelength of light decreases as light propagates through air-glass interface.
View full question & answer→Question 1381 Mark
The interference of light was first demonstrated experimentally by:
Answer
- Thomas Young
Explanation:
Thomas Young demonstrated the phenomenon of interference in water waves.
In 1801, he presented a famous paper to the Royal Society entitled "On the Theory of Light and Colours" which described various interference phenomena, and in 1803 he performed his famous double-slit experiment.
View full question & answer→Question 1391 Mark
Which of the following properties of light conclusively support wave theory of light?
Answer
- Speed of light in water is smaller than the speed in vacuum.
- Light shows interference.
Explanation:
Snell's Law, which states that the speed of light reduces on moving from a rarer to a denser medium, can be concluded from Huygens' wave theory and interference of light waves is based on the wave properties of light.
View full question & answer→Question 1401 Mark
Which of the following is a unit for intensity of light?
Answer
- Both A & B
Explanation:
In photometry, luminous intensity is a measure of the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle, based on the luminosity function, a standardized model of the sensitivity of the human eye. The SI unit of luminous intensity is the candela (cd), an SI base unit.
View full question & answer→Question 1411 Mark
The inability of a lens to bring all the rays coming from a point object to focus at one single point is called:
Question 1421 Mark
A student wants to find if a star if moving away from the earth or towards the earth. Which of the following principle he can use?
Answer
- Red shift of light from other galaxies.
Explanation:
Red shift happens when light from an object increases in wavelength. It occurs whenever a light source moves away from an observer.
Blue shift happens when light from an object decreases in wavelength. It occurs whenever a light source moves toward an observer.
View full question & answer→Question 1431 Mark
When a source of light is receding away from an observer, then the spectral lines will get displaced towards:
Answer
- Red region
Explanation:
When an object moves away from us, its light waves are stretched into lower frequencies or longer wavelengths, and we say that the light is redshifted. It also explain the expanding nature of universe.
Shifting towards red end means wavelength is increasing.
View full question & answer→Question 1441 Mark
When the light source is approaching, the Doppler effect for light is known as:
Answer
- Blue Shift
Explanation:
Optical light with a short wavelength is blue. When the wavelength of the light gets shortened by Doppler effect, we refer to the change in the wavelength as blue shift.
View full question & answer→Question 1451 Mark
Answer
- Cannot detect polarization of light
Explanation:
Polarization changes when plane of vibration of polarized light changes.
Human eye is insensitive to change in polarization and hence, cannot detect polarization of light.
View full question & answer→Question 1461 Mark
The wave-like character was experimentally proved for light by:
Answer
- Young
Explanation:
Newton's particle theory remained accepted for a long time when it was challenged by the double-slit experiment of Thomas Young (1773-1829) in 1801. This experiment clearly established that light coming from two coherent sources interferes and produces maxima and minima depending on the path difference.
View full question & answer→Question 1471 Mark
Consider sunlight incident on a pinhole of width $10^3\mathring{\text{A}}$. The image of the pinhole seen on a screen shall be:
Answer
- Different from a geometrical image.
- Diffused coloured region around a sharp central white spot.
Solution:
Key concept: Diffraction of Light can be observed only if the size of obstacle/aperture is less than the wavelength of light.
Given, width of pinhole $=10^3\mathring{\text{A}}=1000\mathring{\text{A}}$
We know that wavelength of sunlight ranges from $4000\mathring{\text{A}}\text{ to }8000\mathring{\text{A}}$. Clearly, wavelength X < width of the slit.
Hence, light is diffracted from the hole. Due to diffraction from the slit the image formed on the screen will be different from the geometrical image. View full question & answer→Question 1481 Mark
Two lenses of focal lengths $+100\ cm$ and $+5\ cm$ are used to prepare an astronomical telescope. The minimum tube length will be $: ($final image is at $\infty )$
AnswerThe length of telescope $=$ focal length of object $(−f_0) +$focal length of eyepiece
$(f_e) = 100 + 5 $
$= 105\ cm$
View full question & answer→Question 1491 Mark
The phenomenon by which stars recedes from each other is explained by:
Answer
- Red shift
Explanation:
When an object moves away from us, its light waves are stretched into lower frequencies or longer wavelengths, and we say that the light is redshifted. It also explain the expanding nature of universe.
Doppler effect in light explains the phenomenon of receding of stars and approaching of star by red shift and blue shift respectively.
View full question & answer→Question 1501 Mark
Convex lens is not used in:
Answer
- Flood lights
Explanation:
Convex lens always converges the parallel rays but in flood lights, we want to diverge the incident rays so as to light up more area. Thus we use a diverging lens i.e. a concave lens. Thus a convex lens is not used in flood lights.
View full question & answer→Question 1511 Mark
Two light beams superimposed each other constructively this results in$:$
AnswerFor constructive interference,
$A_R = A_{1} + A_{2}$
Due to the constructive interference of the superimposing waves, resultant wave of larger amplitude is obtained and hence constructive interference results in the larger wave.
View full question & answer→Question 1521 Mark
Identify which of the following color light, when passed through a double-slit opening, will produce the widest central band of light on the screen?
Answer
- Red
Explanation:
Fringe width $\beta= \frac{\lambda\text{D}}{\text{d}}$ where λ is the wavelength of the light used
$\Rightarrow\beta\propto\lambda$
As wavelength of the red light is the largest among the visible light, thus fringe width is the greatest formed due to red light. View full question & answer→Question 1531 Mark
At the centre (t = 0) of Newton's ring arrangement, we observe a:
Answer
- Dark spot
Explanation:
In Newton ring experiment, the band forms are circular in nature and at the centre there is presence of dark spot due to destructive interference.
View full question & answer→Question 1541 Mark
The speed of light depends:
Answer
- Neither on elasticity nor on inertia.
Explanation:
The speed of light in any medium depends on the refractive index of that medium, which is an intensive property. Hence, speed of light is not affected by the elasticity and inertia of the medium.
View full question & answer→Question 1551 Mark
The sum of the focal lengths of the objective and an eyepiece, in case of an astronomical telescope. is equal to: (final image is at $\infty$)
Answer
- The length of the telescope
Explanation:
The sum of the focal lengths of the objective and an eyepiece, in case of an astronomical telescope is equal to The length of the telescope.
View full question & answer→Question 1561 Mark
Consider the diffraction patern for a small pinhole. As the size of the hole is increased:
Answer
- The size decreases.
- The intensity increases.
Solution:
Key concept: The "shadow" of hole of diameter d is spread out over an angle $\Delta\theta=1.22\frac{\lambda}{\text{D}}\Rightarrow\ \Delta\theta\propto\frac{1}{\Delta}$
The central bright disc is known as Airy's disc.
As the size of the hole is increased, AO will decrease and size of Airy's disc will decrease.
As the size of the hole is increased, the width of the central maximum of the diffraction pattern of hole decreases. Since the same amount of light is now distributed over a small area, as intensity ∞ 1/area, the area is decreasing so area intensity increases. View full question & answer→Question 1571 Mark
Three waves are given below. I. Sound waves, II. Visible light waves, III. X-rays. Which of the above waves cannot be polarised?
Answer
- I only
Explanation:
Only the transverse waves can be polarized.
As the sound waves are longitudinal waves in nature whereas visible light rays and X-rays are transverse waves.
Thus sound waves cannot be polarized.
View full question & answer→Question 1581 Mark
Wave nature of light is verified by ___________.
Answer
- Interference
Explanation:
Interference
Christian Huygens verified the wave nature of light using interference.
View full question & answer→Question 1591 Mark
Three observers $A, B$ and $C$ measure the speed of light coming from a source to be $vA, 0B$ and $vc.$ The observer $A$ moves towards the source and $C$ moves away from the source at the same speed. The observer $B$ stays stationary. The surrounding space is vacuum everywhere.
AnswerSince the speed of light is a universal constant, $\text{v}_\text{A}=\text{v}_\text{B}=\text{v}_\text{C}=3\times10^8\text{m/s.}$
$\text{v}_\text{B}=\frac{1}{2}(\text{u}_\text{A}+\text{u}_\text{C})$ This expression also implies that $v_A{ = }v_B{ =} v_{C}.$
View full question & answer→Question 1601 Mark
When exposed to sunlight, thin films of oil on water often exhibit brilliant colours due to the phenomenon of:
Answer
- The interference
Explanation:
When exposed to sunlight, thin films of oil on water often exhibit brilliant colors due to the phenomenon of interference.
In the case of a thin oil film, a layer of oil sits atop a layer of water. The oil may have an index of refraction near 1.5 and the water has an index of 1.33.
The materials on either side of the oil film (air and water) both have refractive indices that are less than the index of the film.
View full question & answer→Question 1611 Mark
Two point white dots are 1mm apart on a black paper. They are viewed by eye of pupil of diameter 3mm. Approximately what is the maximum distance up to which these dots can be resolved by the eye.
Question 1621 Mark
Polarisation of light was first successfully explained by:
Answer
- Electromagnetic wave theory
Explanation:
Electromagnetic wave theory explains light as being composed of electric field vibrating in planes.
Polarisation of light refers to vibrating electric field in a particular plane.
View full question & answer→Question 1631 Mark
Light is a form of _______ that we can detect with our ________ .
Answer
- energy, eyes
Explanation:
Light is a form of energy that we can detect with our eyes.
View full question & answer→Question 1641 Mark
Ray optics is valid when characteristic dimensions are:
Answer
- Much larger than the wavelength of light
Explanation:
Ray optics is valid when characteristics dimensions are larger than the wavelength of the light, so that rectilinear property of light can be used.
View full question & answer→Question 1651 Mark
When petrol drops from a vehicle fall over rain water on road surface, colours are seen because of:
Answer
- Interference of light
Explanation:
When a layer of oil falls on water, the light waves reflected by the upper and lower boundaries interfere with one another to produce colours.
Thus the reason is interference of light
View full question & answer→Question 1661 Mark
The wavelength of light visible to eye is of the order of:
AnswerThe range for visible light is between $4\times 10^{−7}m$ to $7\times 10^{−7}m.$
The only wavelength that is present in this range given as an option is $6\times 10^{−7}m.$
View full question & answer→Question 1671 Mark
The colour of bright fringes nearest to the central achromatic fringe in the interference pattern with white light will be:
Answer
- Violet
Explanation:
To observe an interference pattern
$\frac{\text{dy}}{\text{D}}=\text{n}\lambda$
$\text{y}=\frac{\text{nD}\lambda}{\text{d}}$
i.e, for the bright fringes nearest the central achromatic fringe, wavelength must be minimum and in white light wavelength is minimum for violet. View full question & answer→Question 1681 Mark
Why do polarized sun glasses block out some reflected light (glare), but do not block out light that has not been reflected?
Answer
- Some reflected light is at least partially polarized.
Explanation:
When ordinary (unpolarised) light is reflected from a surface, it gets partial polarisation, it means some of the electric vectors in some planes are cut-off. When this partially polarized light is incident on polarized glasses, glass acts as an analyser and therefore block out some reflected light.
View full question & answer→Question 1691 Mark
If one of the two slits of Young's double-slit experiment is painted so that it transmits half the light intensity as the second slit, then:
Answer
- Dark fringes will become less dark and bright fringes will become less bright.
Explanation:
As the intensity from second slit decreases the bright fringe becomes darker due to constructive interference and dark fringe becomes bright due to destructive interference.
View full question & answer→Question 1701 Mark
A very thin film in reflected white light appears:
Answer
- Black
Explanation:
When the film is thin, t → 0, path diff. = $\frac{\lambda}{2}$. Therefore, in reflected light, the film appears black. View full question & answer→Question 1711 Mark
According to Huygens, the ether medium pervading entire universe is:
Answer
- Highly elastic and less dense
Explanation:
Huygen considered, light needs a medium to propagate called ether which is highly elastic and less denser.
View full question & answer→Question 1721 Mark
Corpuscular theory of light was advanced by:
Answer
- Newton
Explanation:
The corpuscular theory was largely developed by Sir Isaac newton. Newton's theory remained in force for more than 100 years and took precedence over Huygen's wave front theory, partly because of Newton’s great prestige.
When the corpuscular theory failed to adequately explain the diffraction, interference and polarization of light it was abandoned in favour of Huygens' wave theory.
View full question & answer→Question 1731 Mark
The following cannot be explained by wave nature of light:
Answer
- Photo electric effect
Explanation:
Photo electric effect
According to wave physics energy of a wave depends upon an amplitude of a wave it means that there light of any frequency can make electrons come out from metal but it did not happen, light of certain fixed frequency can make electron come out from metal. So the photoelectric effect can only be explained by particle nature of light not wave.
View full question & answer→Question 1741 Mark
If L is the coherent length and c the velocity of light, the coherent time is:
Answer
- $\frac{\text{L}}{\text{c}}$
Explanation:
$\text{Coherent time} =\frac{\text{Coherence length}}{\text{Velocity of light}}=\frac{\text{L}}{\text{c}}$ View full question & answer→Question 1751 Mark
Which of the following cannot be polarised?
Answer
- $\beta$ rays
Explanation:
$\beta$ are stream of particles comprising of electrons moving with very high velocity, hence it cannot be polarized, while others can as they are electromagnetic waves. View full question & answer→Question 1761 Mark
Four light waves are represented by
- $\text{y}=\text{a}_1\sin\omega\text{t}$
- $\text{y}=\text{a}_2\sin(\omega\text{t}+\epsilon)$
- $\text{y}=\text{a}_1\sin2\omega\text{t}$
- $\text{y}=\text{a}_2\sin2(\omega\text{t}+\epsilon)$
Interference fringes may be observed due to superposition of:
Answer
- (i) and (ii)
- (iii) and (iv)
Explanation:
The waves are travelling with the same frequencies and varying by constant phase difference.
View full question & answer→MCQ 1771 Mark
In Young's experiment, the distance between the slits is reduced to half and the distance between the slit and screen is doubled, then the fringe width