50 questions · self-marked practice — reveal the answer and mark yourself.
Two unequal resistors are connected in series across a battery. Then the:
The focal length of the objective of a compound microscope is:
A biconvex lens of glass having refractive index 1.47 is immersed in a liquid. It becomes invisible and behaves as a plane glass plate. The refractive index of the liquid is:
Explanation:
For a glass prism, the angle of minimum deviation will be smallest for the light of:
Explanation:
When a ray of light passes through a prism, it disperses the ray of light into seven colours. They are - Violet, Indigo, Blue, Green, Yellow, Orange, Red i.e., VIBGYOR.
The angle of deviation increases in order.
It means that Violet bends the most and Red the least. The extent of bending depends on their wavelength. Red has larger wavelength than blue.
The resistance of a metal wire increases with increasing temperature on account of:
Explanation:
$\rho=\frac{1}{\rho}=\frac{\text{m}}{\text{ne}^2\tau}$
As we increase temperature, average speed of the electrons, which act as the carriers of current, increases resulting in more frequent collisions. The average time of collisions $\tau,$ thus decreases with temperature.
Larger aperture of objective lens in an astronomical telescope:
Explanation:
The larger the objective, the more light the telescope collects and increases the brightness of image.
The field of view of the telescope decreases as the aperture increases, but the resolving power increases.
The objective lens of a telescope forms an real image of the night sky, the size of that image is in proportion to the focal length of the objective lens. It increases with increase in size of objective lens.
The line joining the pole and the centre of curvature of a mirror is called the:
Explantation:
The line joining the pole and the center of curvature of a mirror is called the principal axis.
A ray of light incident at an angle θ on a refracting face of a prism emerges from the other face normally. If the angle of the prism is 5º and the prism is made of a material of refractive index 1.5, the angle of incidence is:
Solution:
Key concept:
In thin prisms, the distance between the refracting surfaces is ineligible and the angle of prism (A) is very small. Since A = r1 + r2, therefore if A is small then both r1, and r2 are also small, and the same is true for i1and i2.
According to Snell's law, $1\sin\text{i}_1=\mu.\sin\text{r}_1\Rightarrow\text{i}_1=\mu.\text{r}_1$
Also, $1.\sin\text{i}_2=\mu.\sin\text{r}_2\Rightarrow\text{i}_2=\mu.\text{r}_2$
Therefore, deviation, $\delta=(\text{i}_1-\text{r}_1)+(\text{i}_2-\text{r}_2)$
$\Rightarrow\ \delta=(\text{i}_1+\text{i}_2)-(\text{r}_1+\text{r}_2)=(\text{r}_1+\text{r}_2)(\mu-1)$
$\Rightarrow\ \delta=\text{A}(\mu-1)$
Since, deviation $\delta=(\mu-1)\text{A}$
$=(1.5-1)\times5^\circ=2.5^\circ$
The angle of the prism is 5º. The ray emerges from refracting face of a prism normally.
Then, i2 = r2 = 0
As A = r1 + r2 ⇒ A or r1 = 5º
But $\text{i}_1=\mu.\text{r}_1=\frac{3}{2}\times5=7.5^\circ$
.......... happens when a wave passes from one medium to another at an angle.
Explanation:
Refraction is a phenomenon in which when a ray passes from one medium to another it bends away from its straight-line path due to the difference in optical densities or refractive indices of the two mediums.
By properly combining two prisms made of different materials, it is possible to:
Explanation:
Consider the case of prisms combined such that the refractive angles are reversed w.r.t. each other. Then, the net deviation of the yellow ray will be,
$\delta_\text{y}=(\mu_\text{y}-1)\text{A}-(\mu_\text{y}'-1)\text{A}'$
And, the net angular dispersion will be
$\delta_\text{y}-\delta_\text{r}=(\mu_\text{y}-1)\text{A}(\omega-\omega')$
Thus, by choosing appropriate conditions, we can have the above mentioned cases.
What kind of image is obtained always for concave lens?
Explanation:
As can be seen in image, Virtual, Erect and Diminished image is obtained always for concave lens.
The central point of a spherical mirror is called:
Explanation:
The central point of a spherical mirror is called the Pole of the mirror.
An achromatic combination of lenses produce:
Explanation:
An achromatic combination of lenses provide deviation without dispersion. So, images are unaffected by variation of refractive index with wavelength.
Two concave lenses L1 and L2 are kept in contact with each other. If the space between the two lenses is filled with a material of refractive index $\mu\approx1,$ the magnitude of the focal length of the combination:
Explanation:
$\frac{1}{\text{f}}=\frac{1}{\text{f}_{\text{L}_1}}+\frac{1}{\text{f}_{\text{L}_2}}$
$\frac{1}{\text{f}_{\text{L}_1}}=(\mu-1)\Big(\frac{-2}{\text{R}}\Big)=\frac{1}{\text{f}_{\text{L}_2}}$
Local length of the combination.
$\frac{1}{\text{f}}=(\mu-1)\Big(\frac{-2}{\text{R}}\Big)+(\mu-1)\Big(\frac{-2}{\text{R}}\Big)$
$\frac{1}{\text{f}}=-4(\mu-1)\Big(\frac{1}{\text{R}}\Big)$
$\text{f}=\frac{\text{R}}{4(\mu-1)}$
Where $\text{f}_{\text{L}_1}=\text{f}_{\text{L}_2}=\frac{\text{R}}{2(\mu-1)}$
$(\text{f}_{\text{L}_1}=\text{f}_{\text{L}_2})>\text{f}$
The magnifying power of a simple microscope can be increased if we use an eyepiece of:
Explanation:
The only difference between simple microscope and compound microscope is an eyepiece of smaller focal length than objective which increases magnifying power.
Consider three converging lenses L1, L2 and L3 having identical geometrical construction. The index of refraction of L1 and L2 are $\mu_1$ and $\mu_2$ respectively. The upper half of the lens L3 has a refractive index $\mu_1$ and the lower half has $\mu_2$. A point object O is imaged at O1 by the lens L1 and at O2 by the lens L2 placed in same position. If L3 is placed at the same place:
Explanation:
It rays are Passing through m1 then Image will be form at "O1" and If rays are Passing through m2 then Image will be form at "O2".
A passenger in an aeroplane shall:
Solution:
As aeroplane is at higher altitude, the passenger in an aeroplane may see a primary and a secondary rainbow like concentric circles.
Key Concept:
Magnification of an optical instrument is expressed in:
Explantion:
$\text{Magnification}=\frac{\text{Image Height}}{\text{Object Height}} $
because unit of image height and object height is same hence unit of magnification is none because it is a constant number. So, it has got to unit.
If the light moving in a straight line bends by a small but fixed angle, it may be a case of:
Explanation:
When the light strikes on a surface nearly parallel to it, it then bends by a small and fixed angle after reflection. Also, when the light travels from one medium to another with slight differences in their refractive indices, it bends by a small angle. Thus, the bending of light by a small but fixed angle can be the case of either reflection or refraction.
What type of lens from the following would you have in your magnifying lens to read a page in small print?
Explanation:
A concave lens always produces virtual, erect and diminished images and the decrease in the size of the image depends on the position of the object.
Concave lens will shrink the size of the already small letters. Hence, it is undesirable.
A convex lens produces real and virtual, erect and inverted, diminished, same sized and magnified image of the object, depending upon the position of the object on the principal axis.
When the object is placed at a distance less than the focal length of convex lens, an enlarged and erect image of the object is formed, which will make it easier to read small letters.
A glass slab is placed in the path of beam of convergent light. The point of convergence of light:
Explanation:
As a glass has refractive index of $\frac{3}{2}$ with respect to air, the convergent light will bend towards the normal in the glass and again bend away from the normal, but in the whole process the beam is displaced parallel to initial path as shown in figure and converge at a greater distance from the glass slab.
Two rays A and B being reflected by a mirror and going as A' and B'. The mirror:
Explanation:
Here initially A & B is parallel to each other after reflection by teh plane mirror A' & B' goes Parallel to each other.
If a glass prism is dipped in water, its dispersive power:
Explanation:
If $\mu$ is the refractive index and A is the angle of prism, then the angular dispersion produced by the prism will be given by $\delta=(\mu-1)\text{A}.$
Because the relative refractive index of glass with respect to water is small compared to the refractive of glass with respect to air, the dispersive power of the glass prism is more in air than that in water.
The rays of different colors fail to converge at a point after going through a converging lens. This defect is called _________.
Explanation:
Chromatic aberation is the defect due to which rays of different wavelength converge at various point after passing through converging lens. It is due to varying refractive index for various wavelength.
In producing a pure spectrum, the incident light is passed through a narrow slit placed in the focal plane of an achromatic lens because a narrow slit:
Explanation:
To produce a pure spectrum, a parallel light beam is required to be incident on the dispersing element. So, the incident light is passed through a narrow slit placed in the focal plane of an achromatic lens.
A narrow beam of white light goes through a slab having parallel faces.
Explanation:
White light will split into different colours inside the glass slab because the value of refractive index is different for different wavelengths of light; thus, they suffer different deviations. But the emergent light will be white light. As the faces of the glass slide are parallel, the emerging lights of different wavelengths will reunite after refraction.
A man is looking at a small object placed at his near point. Without altering the position of his eye or the object, he puts a simple microscope of magnifying power 5X before his eyes. The angular magnification achieved is:
We have,
h = Object height
u = Object distance = 25cm
D = Near point = 25cm
Now,
Between the primary and secondary rainbows, there is a dark band known as Alexandar’s dark band. This is because:
Solution:
The Alexandar's dark band lies between the primary and secondary rainbows, formed due to light scattered into this region interfere destructively. The primary rainbows subtends an angle nearly 41º to 42º at observer's eye, whereas secondary rainbows subtends an angle nearly 51º to 54º at observer's eye w.r.t. incident light ray.
Hence, the scattered rays with respect to the incident light of the sun lies between approximately 42º and 50º.
A short pulse of white light is incident from air to a glass slab at normal incidence. After travelling through the slab, the first colour to emerge is:
Solution:
As velocity of wave is given by the relation $\text{v}=\text{f}\lambda$. When light ray goes from one medium to other medium, the frequency of light remains unchanged. Hence $\text{v}\propto\lambda$ or greater the wavelength, greater the speed.
The light of red colour is of highest wavelength and therefore of highest speed. Therefore, after travelling through the slab, the red colour emerges first.
The bending of light as it passes from one medium into another is commonly known as:
Explanation:
In refraction ray of light passes from one medium to another medium. The ray of light bends towards normal in the denser medium.
There are certain material developed in laboratories which have a negative refractive index (Fig). A ray incident from air (medium 1) into such a medium (medium 2) shall follow a path given by:
Solution:
The materials with negative refractive index responds to Snell’s law just opposite way. If incident ray from air (Medium 1) incident on those material, the ray refract or bend same side of the normal as in option (a).
A manufacturer uses a concave lens instead of a convex lens in a magnifying glass by mistake. What will be the effect on the working of the lens?
Explanation:
Images formed by a concave lens are always diminished.
The refraction of light is commonly known as:
Explanation:
The refraction of light is commonly known as bending.
The refracted rays bend towards the normal when they enter from rarer to denser medium.
The refracted rays bend away from the normal when they enter from denser to rarer medium.
Which of the following (referred to a spherical mirror) do (does) not depend on whether the rays are paraxial or not?
Pole.
Focus.
Principal axis.
Explanation:
If Paraxial rays comes to parallel to the spherical mirror is pasees to the Focus of the spherical mirror.
A point object is placed at a distance of 30cm from a convex mirror of focal length 30cm. The image will form at:
Explanation:
By mirror formula:
$\frac{1}{\text{V}}+\frac{1}{\text{u}}=\frac{1}{\text{f}}$
Here u = -30cm
f = +30cm
So, $\frac{1}{\text{V}}-\frac{1}{30}=\frac{1}{30}$
Þ v= 15cm behind the mirror.
A thin lens is made with a material having refractive index $\mu=1.5.$ Both the sides are convex. It is dipped in water $(\mu=1.33).$ It will behave like:
Explanation:
Here P, P1 & P2 are the power of Lenses.
P = P1 + P2
$\frac{1}{\text{f}}=\frac{1}{\text{f}_1}+\frac{1}{\text{f}_2}$
$=(\mu-1)\Big(\frac{2}{\text{R}}\Big)+(\mu'-1)\Big(\frac{-1}{\text{R}}\Big)$
$=\Big(\frac{3}{2}-1\Big)\Big(\frac{2}{\text{R}}\Big)-\Big(\frac{4}{3}-1\Big)\Big(\frac{1}{\text{R}}\Big)$
$\frac{1}{\text{f}}=\frac{1}{\text{R}}-\frac{1}{3\text{R}}$
$\frac{1}{\text{f}}=\frac{3-1}{3\text{R}}$
$\text{f}=\frac{3\text{R}}{2}$
focal length of combined is positive means it will behave like a canvergent lens.
The radius of curvature of the curved surface of a plano-convex lens is 20cm. If the refractive index of the material of the lens be 1.5, it will.
Solution:
We know that, $\text{f}=\frac{\text{R}}{\mu-1}$
Substituting $\text{R}=20\text{cm},\mu=1.5,$ we get
$\text{f}=\frac{20}{1.5-1}=40\text{cm}$
Since, the focal length is greater than zero.
Therefore, lens act as a convex lens irrespective of the side on which the object lies.
A point object O is placed on the principal axis of a convex lens of focal length f = 20cm at a distance of 40cm to the left of it. The diameter of the lens is 10cm. An eye is placed 60cm to right of the lens and a distance h below the principal axis. The maximum value of h to see the image is:
Explanation:
$\tan\theta=\frac{5}{40}=\frac{\text{h}}{20}$
$\text{h}=\frac{5}{2}=\frac{\text{h}}{20}$
$\text{h}=\frac{5}{2}=2.5\text{cm}$
The maximum value of "h =2.5cm" to see the Image of the object.
A double convex lens has two surfaces of equal radii R and refractive index $\mu=1.5$ We have,
$\text{f}=2\text{R}$
Explanation:
$\Rightarrow\frac{1}{\text{f}}=(\mu-1)\Big(\frac{1}{\text{R}_1}-\frac{1}{\text{R}_2}\Big)$
$\Rightarrow\frac{1}{\text{f}}=\Big(\frac{3}{2}-1\Big)\Big(\frac{1}{\text{R}}-\Big(-\frac{1}{\text{R}}\Big)\Big)$
$\frac{1}{\text{f}}=\frac{1}{\text{R}}$
$\text{f}=\text{R}$
The shift by which object appears to be raised ....... with the increase in the thickness of the denser medium.
Explanation:
The shift increase with the increase in the thickness of the denser medium, but the shift decrease with the increase in wavelength of light used.
Select the correct alternative, The angle between the normal and refracted ray is called:
Explanation:
The angle formed between the normal and refracted ray at the point of refraction is called angle of refraction.
A normal eye is not able to see objects closer than 25cm because:
Explanation:
The ciliary muscles adjust the focal length to form an image on the retina, but the muscles cannot be strained beyond a limit. Hence, if the object is brought too close to the eye, the focal length cannot be adjusted to form the image on the retina.
A parallel beam of light is incident on a converging lens parallel to its principal axis. As one moves away from the lens on the other side on its principal axis, the intensity of light:
Explanation:
The intensity o light is first increases then decreases.
A symmetric double convex lens is cut in two equal parts by a plane perpendicular to the principal axis. If the power of the original lens was 4D, the power of a cutlens will be:
Explanation:
Before cut
$\frac{1}{\text{f}}=(\mu-1)\Big(\frac{2}{\text{R}}\Big)=4\text{D} \ ...(1)$
After cut
$\frac{1}{\text{f}_1}=(\mu-1)\Big(\frac{1}{\text{R}}\Big)+\frac{1}{\text{f}_2}=(\mu-1)\Big(\frac{1}{2}\Big) \ ...(2)$
From eq. (1) we get Power of f1 = power of f2
$\text{P}=\frac{1}{\text{f}_1}=\frac{1}{\text{f}_2}=2\text{D}$
A point source of light is placed at a distance, of 2f from a converging lens of focal length f. The intensity on the other side of the lens is maximum at a distance:
Explanation:
The Intensity on the other side of the lans is maximum at a distance 2f.
In which of the following the final image is erect?
Explanation:
In a simple microscope, the image formed is virtual and above the axis on the same side of the object. Similarly, in a Galilean telescope, the image formed is virtual, erect and magnified and between the objective lens and the eyepiece. A compound microscope and an astronomical telescope produce inverted images.
A thin lens with focal length f to be used as magnifying glass. Which of the following statements regarding the situation is true?
Explanation:
A converging lens, magnifies the image of an object if it is placed at a distance less than the focal length of the lens.
The phenomena involved in the reflection of radiowaves by ionosphere is similar to:
Solution:
Radio waves are reflected by a layer of atmosphere called the Ionosphere, so they can reach distant parts of the Earth. The reflection of radio waves by ionosphere is due to total internal reflection. It is the same as total internal reflection of light in air during a mirage, i.e., angle of incidence is greater than critical angle.
Important point: The ionized part of the Earth’s atmosphere is known as the ionosphere. Ultraviolet light from the sun collides with atoms in this region knocking electrons loose. The creates ions, or atoms with missing electrons. This is what gives the Ionosphere its name- and it is the free electrons that cause the reflection and absorption of ratio waves.
Which of the following would you prefer to use while reading small letters found in a dictionary?
Explanation:
Convex lens can form an erect, virtual and enlarged image when the object is positioned between its pole and focus.
A tall man of height 6 feet, want to see his full image. Then required minimum length of the mirror will be-