Question types

Light Waves question types

79 questions across 6 question groups — pick any mix to generate a Physics paper with step-by-step answer keys.

79
Questions
6
Question groups
5
Question types
Sample Questions

Light Waves questions

One sample from each question group in this chapter. Select any group above to see the full set with answer keys.

Q 1M.C.Q [1M]1 Mark
The equation of a light wave is written as $\text{y}=\text{A}\ \sin(\kappa\text{x}-\omega\text{t}).$ Here, y represents:
  1. Displacement of either particles.
  2. Pressure in the medium.
  3. Density of the medium.
  4. Electric field.
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Q 2M.C.Q [1M]1 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:

  1. $0^\circ$

  2. $45^\circ$

  3. $90^\circ$

  4. $\cos^{-1}\Big(\frac{1}{\sqrt{3}}\Big)$

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Q 3M.C.Q [1M]1 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.

  1. $\text{v}_\text{A}>\text{v}_\text{B}>\text{v}_\text{C}.$

  2. $\text{v}_\text{A}<\text{v}_\text{B}<\text{v}_\text{C}$

  3. $\text{v}_\text{A}=\text{v}_\text{B}=\text{v}_\text{C}$

  4. $\text{v}_\text{B}=\frac{1}{2}(\text{v}_\text{A}+\text{v}_\text{C})$

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Q 4M.C.Q [1M]1 Mark
If the source of light used in a Young's double slit experiment is changed from red to violet:
  1. The fringes will become brighter.
  2. Consecutive fringes will come closer.
  3. The intensity of minima will increase.
  4. The central bright fringe will become a dark fringe.
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Consider the situation of the previous problem. If the mirror reflects only 64% of the light energy falling on it, what will be the ratio of the maximum to the minimum intensity in the interference pattern observed on the screen?
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Find the thickness of a plate which will produce a change in optical path equal to half the wavelength $\lambda$ of the light passing through it normally. The refractive index of the plate is $\mu$.
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Plane microwaves are incident on a long slit having a width of 5.0cm. Calculate the wavelength of the microwaves if the first diffraction minimum is formed at $\theta=30^\circ.$
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A source emitting light of wavelengths 480nm and 600nm is used in. a double slit interference experiment. The separation between the slits is 0.25mm and the interference is observed on a screen placed at 150cm from the slits. Find the linear separation between the first maximum (next to the central maximum) corresponding to the two wavelengths.
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If we put a cardboard (say 20cm × 20cm) between a light source and our eyes, we can't see the light. But when we put the same cardboard between a sound source and our ear, we hear the sound almost clearly. Explain.
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Q 143 Marks Question3 Marks
Two narrow slits emitting iight in phase are separated by a distance of 1.0cm. The wavelength of the light is 5.0 × 10-7m. The interference pattern is observed on a screen placed at a distance of 1.0m.
  1. Find the separation between the consecutive maxima. Can you expect to distinguish between these maxima?
  2. Find the separation between the sources which will give a separation of 1.0mm between the consecutive maxima.
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Q 153 Marks Question3 Marks
A narrow slit S transmitting light of wavelength $\lambda$ is placed a distance d above a large plane mirror as shown in figure (17-E1). The light coming directly from the slit and that coming after the reflection interfere at a screen $\sum$ placed at a distance D from the slit.

  1. What will be the intensity at a point just above the mirror, i.e., just above O?
  2. At what distance from 0 does the first maximum occur?
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Q 163 Marks Question3 Marks
The index of refraction of fused quartz is 1.472 for light of wavelength 400nm and is 1.452 for light of wavelength 760nm. Find the speeds of light of these wavelengths in fused quartz.
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Q 173 Marks Question3 Marks
Suppose white light falls on a double slit but one slit is covered by a violet filter (allowing $\lambda=400\text{nm}$). Describe the nature of the fringe pattern observed.
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Q 183 Marks Question3 Marks
Is the colour of 620nm light and 780nm light same? Is the colour of 620nm light and 621nm light same? How many colours are there in white light?
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TV signals broadcast by Delhi studio cannot be directly received at Patna which is about 1000km away. But the same signal goes some 36000km away to a satellite, gets reflected and is then received at Patna. Explain.
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Why don't we have interference when two candles are placed close to each other and the intensity is seen at a distant screen? What happens if the candles are replaced by laser sources?
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Consider the arrangement shown in figure (17-E4). The distance D is large compared to the separation d between the slits.
  1. Find the minimum value of d so that there is a dark fringe at 0.
  2. Suppose d has this value. Find the distance x at which the next bright fringe is formed.
  3. Find the fringe-width.

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A glass surface is coated by an oil film of uniform thickness 1.00 × 10-4cm. The index of refraction of the oil is 1.25 and that of the glass is 1.50. Find the wavelengths of light in the visible region (400nm - 750nm) which are completely transmitted by the oil film under normal incidence.
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Two coherent point sources S1 and S2 vibrating in phase emit light of wavelength $\lambda$. The separation between the sources is $2\lambda$. Consider a line passing through S2 and perpendicular to the line S1S2. What is the smallest distance from S2 where a minimum of intensity occurs?
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Consider the arrangement shown in figure. By some mechanism, the separation between the slits S3 and S4 can be changed. The intensity is measured at the point P which is at the common perpendicular bisector

of S1S2 and S3S4. When $\text{z}=\frac{\text{D}\lambda}{2\text{d}},$ intensity measured at P is I. Find this intensity when z is equal to:

  1. $\frac{\text{D}\lambda}{\text{d}}$

  2. $\frac{3\text{D}\lambda}{2\text{d}}$

  3. $\frac{2\text{D}\lambda}{\text{d}}$

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