# MCQ Questions Chapter 10 Wave Optics Class 12 Physics

Please refer to MCQ Questions Chapter 10 Wave Optics Class 12 Physics with answers provided below. These multiple-choice questions have been developed based on the latest NCERT book for class 12 Physics issued for the current academic year. We have provided MCQ Questions for Class 12 Physics for all chapters on our website. Students should learn the objective based questions for Chapter 10 Wave Optics in Class 12 Physics provided below to get more marks in exams.

## Chapter 10 Wave Optics MCQ Questions

Please refer to the following Chapter 10 Wave Optics MCQ Questions Class 12 Physics with solutions for all important topics in the chapter.

MCQ Questions Answers for Chapter 10 Wave Optics Class 12 Physics

Question. Beyond which frequency, the ionosphere ends any incident electromagnetic radiation but do not reflect it back towards the earth?
(a) 50 MHz
(b) 40 MHz
(c) 30 MHz
(d) 20 MHz

B

Question. Sky wave propagation is used in
(b) satellite communication
(c) TV communication
(d) Both TV and satellite communication

A

Question. The frequency of a FM transmitter without signal input is called
(a) the centre frequency
(b) modulation
(c) the frequency deviation
(d) the carrier swing

A

Question. The amplitude of an electromagnetic wave in vacuum is doubled with no other changes made to the wave. As a result of this doubling of the amplitude, which of the following statement is correct?
(a) The frequency of the wave changes only.
(b) The wavelength of the wave changes only.
(c) The speed of wave propagation changes only.
(d) None of the above is correct.

D

Question. If a radio receiver amplifies all the signal frequencies equally well, it is said to have high
(a) sensitivity
(b) selectivity
(c) distortion
(d) fidelity

D

Question. Polarising angle for water is 53°4′. If light is incident at this angle on the surface of water and reflected the angle of refraction is
(a) 53°4′
(b) 126°56′
(c) 36°56′
(d) 30°4′

C

Question. In Young’s double slit experiment, the spacing between the slits is d and wavelength of light used is 6000 Å. If the angular width of a fringe formed on a distant screen is 1°, then value of d is
(a) 1 mm
(b) 0.05 mm
(c) 0.03 mm
(d) 0.01 mm

C

Question. In an electromagnetic wave, the average energy density associated with magnetic field is
(a) Li02/2
(b) B2/2μ0
(c) μ0B2/2
(d) μu/2B2

B

Question. An electromagnetic wave going through vacuum is described by E = E0 sin(kx – ϖt) Which of the following is/are independent of the wavelength?
(a) k
(b) ϖ2
(c) k/ϖ
(d) kϖ2

C

Question. In Young’s double slit experiment, the intensity of light at a point on the screen where the path different is λ = I. The intensity of light at point where the path difference becomes λ/3 is
(a) λ/4
(b) λ/3
(c) λ/2
(d) λ

A

Question. Sinusoidal carrier voltage of frequency 1.5 MHz and amplitude 50 V is amplitude modulated by sinusoidal voltage of frequency 10 kHz producing 50% modulation. The lower and upper side-band frequencies in kHz are
(a) 1490, 1510
(b) 1510, 1490
(c) 1/1490, 1/1510
(d) 1/1510, 1/1490

A

Question. Two identical light sources S1 and S2 emit light of same wavelength λ. These light rays will exhibit interference if
(a) their phase differences remain constant
(b) their phases are distributed randomly
(c) their light intensities remain constant
(d) their light intensities change randomly

A

Question. In a double slit experiment, 5th dark fringe is formed opposite to one of the slits, the wavelength of light is
(a) d2/6D
(b) d2/5D
(c) d2/15D
(d) d2/9D

D

Question. Which of the following rays is emitted by a human body?
(a) X-rays
(b) UV rays
(c) Visible rays
(d) IR rays

D

Question. Two light sources are said to be coherent if they are obtained from
(a) two independent point sources emitting light of the same wavelength
(b) a single point source
(c) a wide source
(d) two ordinary bulbs emitting light of different wavelengths

B

Question. Radio waves diffract around building although light waves do not. The reason is that radio waves
(a) travel with speed larger than c
(b) have much larger wavelength than light
(c) carry news
(d) are not electromagnetic waves

B

Question. An AM wave has 1800 W of total power content. For 100% modulation the carrier should have power content equal to
(a) 1000 W
(b) 1200 W
(c) 1500 W
(d) 1600 W

B

Question. Four light sources produce the following four waves :
(i) y1 = a sin (ϖt + Φ1)
(ii) y2 = a sin 2ϖt
(iii) y3 = a′ sin (ϖt + Φ2)
(iv) y4 = a′ sin (3ϖt + Φ)
Superposition of which two waves give rise to interference?
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (i) and (iii)
(d) (iii) and (iv)

C

Question. A radio station has two channels. One is AM at 1020 kHz and the other FM at 89.5 MHz. For good results you will use
(a) longer antenna for the AM channel and shorter for the FM
(b) shorter antenna for the AM channel and longer for the FM
(c) same length antenna will work for both
(d) information given is not enough to say which one to use for which.

B

Question. Two light rays having the same wavelength l in vacuum are in phase initially. Then the first ray travels a path l1 through a medium of refractive index n1 while the second ray travels a path of length l2 through a medium of refractive index n2. The two waves are then combined to observe interference. The phase difference between the two waves is

B

Question. In the Young’s double slit experiment, the intensities at two points P1 and P2 on the screen are respectively I1 and I2. If P1 is located at the centre of a bright fringe and P2 is located at a distance equal to a quarter of fringe width from P1, then I1/Iis
(a) 2
(b) 1/2
(c) 4
(d) 16

A

Question. In Young’s double slit experiment, the 10th maximum of wavelength λ1 is at a distance of y1 from the central maximum. When the wavelength of the source is changed to λ2, 5th maximum is at a distance of y2 from its central maximum. The ratio (y1/y2) is

A

Question. A parallel beam of fast moving electrons is incident normally on a narrow slit. A screen is placed at a large distance from the slit. If the speed of the electrons is increased, which of the following statement is correct?
(a) Diffraction pattern is not observed on the screen in the case of electrons
(b) The angular width of the central maximum of the diffraction pattern will increase
(c) The angular width of the central maximum will decrease
(d) The angular width of the central maximum will remain the same.

C

Question. In Young’s double slit experiment, the interference pattern is found to have an intensity ratio between bright and dark fringes is 9. This implies that
(a) the intensities at the screen due to two slits are 5 units and 4 units respectively
(b) the intensities at the screen due to the two slits are 4 units and 1 units, respectively
(c) the amplitude ratio is 7
(d) the amplitude ratio is 6

B

Question. Indicate which one of the following statements is not correct?
(a) Intensities of reflections from different crystallographic planes are equal
(b) According to Bragg’s law higher order of reflections have high q values for a given wavelength of radiation
(c) For a given wavelength of radiation, there is smallest distance between the crystallographic planes which can be determined
(d) Bragg’s law may predict a reflection from a crystallographic plane to be present but it may be absent due to the crystal symmetry

A

Question. Two beams of light will not give rise to an interference pattern, if
(a) they are coherent
(b) they have the same wavelength
(c) they are linearly polarized perpendicular to each other
(d) they are not monochromatic.

C

Question. A slit of width a is illuminated with a monochromatic light of wavelength λ from a distant source and the diffraction pattern is observed on a screen placed at a distance D from the slit. To increase the width of the central maximum one should
(a) decrease D
(b) decrease a
(c) decrease λ
(d) the width cannot be changed.

B

Question. The antenna current of an AM transmitter is 8 A when only the carrier is sent, but it increases to 8.93 A when the carrier is percentage modulation.
(a) 60.1%
(b) 70.1%
(c) 80.1%
(d) 50.1%

B

Question. Following diffraction pattern was obtained using a diffraction grating using two different wavelengths λ1 and λ2. With the help of the figure identify which is the longer wavelength and their ratios.

(a) λ2 is longer than λ1 and the ratio of the longer to the shorter wavelength is 1.5
(b) λ1 is longer than λ2 and the ratio of the longer to the shorter wavelength is 1.5
(c) λ1 and λ2 are equal and their ratio is 1.0
(d) λ2 is longer than λ1 and the ratio of the longer to the shorter wavelength is 2.5

C

Question. Phase difference between any two points of a wavefront is
(A) π
(B) π/2
(C) 0
(D) π/4

C

Question. A thin film of soap solution (n = 1.4) lies on the top of a glass plate (n = 1.5). When visible light is incident almost normal to the plate, two adjacent reflection maxima are observed at two wavelengths 420 and 630 nm. The minimum thickness of the soap solution is
(a) 420 nm
(b) 450 nm
(c) 630 nm
(d) 1260 nm.

B

Question. Radar waves are sent towards a moving aeroplane and the reflected waves are received. When the aeroplane is moving towards the radar, the wavelength of the wave
(a) decreases
(b) increases
(c) remains the same
(d) sometimes increases or decreases

A

Question. Wavefront generated from a line source is
(A) cylindrical wavefront
(B) spherical wavefront
(C) plane wavefront
(D) either (A) or (B)

A

Question. Which of the following statement is true?
(A) According to both Maxwell’s electromagnetic theory and Huygens wave theory light is treated as a wave in nature and require
medium to travel.
(B) According to both Maxwell’s electromagnetic theory and Huygens wave theory light is treated as a particle in nature and require medium to travel.
(C) According to both Maxwell’s electromagnetic theory and Huygens wave theory light is treated as a wave in nature and does not require medium to travel.
(D) According to Maxwell’s electromagnetic theory light is treated as a wave in nature and require no medium to travel. According to Huygens theory light is treated as a wave in nature and require medium to travel.

D

Question. In Huygens theory, light waves
(A) are transverse waves and require a medium to travel.
(B) are longitudinal waves and require a medium to travel.
(C) are transverse waves and require no medium to travel.
(D) are longitudinal waves and require no medium to travel.

B

Question. Huygens theory could not explain
(A) photoelectric effect.
(B) reflection of light.
(C) diffraction of light.
(D) interference of light.

A

Question. 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,
(A) there shall be alternate interference patterns of red and blue.
(B) there shall be an interference pattern for red distinct from that for blue.
(C) there shall be no interference fringes.
(D) there shall be an interference pattern for red mixing with one for blue.

C

Question. A Young’s double slit experiment is performed with blue (wavelength 460 nm) and green light (wavelength 550 nm) respectively. If y is the distance of 4th maximum from the central fringe then
(A) yB = yG
(B) yB > yG
(C) yG > yB
(D) yB/yG = 550/460

C

Question. Figure shows a standard two-slit arrangement with slits S1, S2. P1, P2 are the two minima points on either side of P shows in Figure. At P2 on the screen, there is a hole and behind P2 is a 2-slit arrangement with slits S3 and S4 and a second screen behind them.

(A) There would be no interference pattern on the second screen but it would be lighted.
(B) The second screen would be totally dark.
(C) There would be a single bright point on the second screen.
(D) There would be a regular two slit pattern on the second screen.

D

Question. In Young’s double slit experiment, the distance between the slits is reduced to half and the distance between the slits and the screen is doubled. The fringe width
(A) will be double.
(B) will be half.
(C) will remain same.
(D) will be four times.

D

Question. A Young’s Double slit experiment is performed in air and in water. Which of the following relationship is true regarding fringe width (β)?
(A) βAIR > βWATER
(B) βWATER > βAIR
(C) βAIR = βWATER
(D) βWATER = 0

A

Question. When a monochromatic light is passed around a fine wire a diffraction pattern is observed. How the fringe width will change by increasing the diameter?
(A) Fringe width has no relation with the diameter of wire
(B) Increases
(C) Decreases
(D) Fringe width changes with change of wavelength only

C

Question. The penetration of light into the region of geometrical shadow is known as
(A) interference of light.
(B) diffraction of light.
(C) refraction of light.
(D) polarisation of light.

B

Question. Angular width of central maxima of a single slit diffraction pattern is independent of
(A) slit width
(B) frequency of the light used
(C) wavelength of the light used
(D) distance between slit and screen

D

Question. The main condition for diffraction to be observed is
(A) size of obstacle should be comparable to the wavelength of the wave
(B) size of obstacle should be much larger than the wavelength of the wave
(C) size of obstacle should be much smaller than the wavelength of the wave
(D) for any size of obstacle

A

Assertion and Reason Based MCQs

Directions: In the following questions, a statement of Assertion (A) is followed by a statement of Reason (R).
Mark the correct choice as:
(A) Both (A) and (R) are true, and (R) is the correct explanation of (A).
(B) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
(C) (A) is true, but (R) is false.
(D) (A) is false, but (R) is true.

Question. Assertion (A): According to Huygens theory no back-ward wavefront is possible.
Reason (R):
Amplitude of secondary wavelets is proportional to (1 + cos q), where q is the angle between the ray at the point of consideration and direction of secondary wavelet.

A

Question. Assertion (A): Fringes of interference pattern produced by blue light is narrower than that produced by red light.
Reason (R): In Young’s double slit experiment, fringe width= lD/d

A

Question. Assertion (A): When a light wave travels from rarer to denser medium, its speed decreases. Due to this reduction of speed the energy carried by the light wave reduces.
Reason (R): Energy of wave is proportional to the frequency.

D

Question. Assertion (A): Wavefront emitted by a point source of light in an isotropic medium is spherical.
Reason (R): Isotropic medium has same refractive index in all directions.

A

Question. Assertion (A): No interference pattern is detected when two coherent sources are too close to each other.
Reason (R): The fringe width is inversely proportional to the distance between the two slits.

A

Question. Assertion (A): Diffraction takes place with all types of waves.
Reason (R): Diffraction is perceptible when the wavelength of the wave is comparable to the dimension of the diffracting device.

B

Question. Assertion (A): For best contrast between maxima and minima in the interference pattern of Young’s double slit experiment, the amplitudes of light waves emerging from the two sources should be equal.
Reason (R): For interference, the sources must be coherent.

B

Case-based MCQs

I. Read the following text and answer the following questions on the basis of the same:
In one of his experiments on interference, August Jean Fresnel used a biprism to induce interference between two beams. He split a diverging beam of light into two parts by using the biprism to refract them. This resulted in two split beams which acted as if they were from two coherent sources and which therefore interfered with each other.
A Fresnel Biprism is a thin double prism placed base to base and have very small refracting angle ( 0.5°). This is equivalent to a single prism with one of its angle nearly 179° and other two of 0.5° each.

In Young’s double Slits experiment, a single source is split in two coherent sources. For the Young’s slits experiment, we must approximate that the slits act as point sources. This however is not the case, since the slits have finite width. In this way, it gives rise to unwanted diffraction effects that causes errors. The Fresnel biprism experiment overcomes this problem.
A Fresnel biprism is a variation of Young’s Slits experiment. When monochromatic light through a narrow slit falls on biprism that divides it into two components. One of these component is refracted from upper portion of biprism and the other one refracted through lower portion. Two virtual coherent sources formed from the original source. In this case, two virtual coherent sources are point sources and replace slits in Young’s experiment.

Question. Base angles of Fresnel biprism are:
(A) 179°
(B) 90°
(C) 0.50°
(D) None of these

C

Question. Which problem of Young’s double slit experiment is overcome by Fresnel biprism?
(A) Young’s double slit arrangement gives rise to irregular interference fringe pattern which is overcome by Fresnel biprism which produces coherent sources by refraction in a prism
(B) Finite width of slits in Young’s double slit experiment gives rise to unwanted diffraction effects that causes errors. This is overcome by Fresnel biprism by producing virtual coherent point sources.
(C) Young’s double slit arrangement produces interference fringe pattern of low intensity which is overcome by Fresnel biprism.
(D) All of the above

B

Question. Fresnel biprism produces:
(A) two real coherent sources.
(B) two virtual coherent sources.
(C) a number of real coherent sources.
(D) a number of virtual coherent sources.

B

Question. The Fresnel biprism is:
(A) a combination of two prisms with their bases in contact.
(B) a combination of two prisms with their refracting surfaces in contact.
(C) single prism
(D) not a prism actually.

A

Question. What is the difference between the coherent sources produced by Young’s double slit arrangement and Fresnel biprism?
(A) Young’s double slit arrangement produces virtual coherent sources whereas Fresnel biprism produces real coherent sources
(B) Young’s double slit arrangement produces coherent point sources whereas Fresnel biprism produces coherent sources which are not point sources
(C) Both Young’s double slit arrangement and Fresnel biprism produce similar coherent sources
(D) Fresnel birism produces virtual coherent point sources whereas Young’s double slit arrangement produces real coherent sources which are not point sources.

D

II. Read the following text and answer the following questions on the basis of the same:
Diffraction in a hall:
A and B went to purchase a ticket of a music programme. But unfortunately only one ticket was left. They purchased the single ticket and decided that A would be in the hall during the 1st half and B during the 2nd half.
Both of them reached the hall together. A entered the hall and found that the seat was behind a pillar which creates an obstacle. He was disappointed. He thought that he would not be able to hear the programme properly.
B was waiting outside the closed door. The door was not fully closed. There was a little opening. But surprisingly, A could hear the music programme.
This happened due to diffraction of sound.
The fact we hear sounds around corners and around barriers involves both diffraction and reflection of sound. Diffraction in such cases helps the sound to “bend around” the obstacles.
In fact, diffraction is more pronounced with longer wavelengths implies that we can hear low frequencies around obstacles better than high frequencies.
B was outside the door. He could also hear the programme. But he noticed that when the door opening is comparatively less he could hear the programme even being little away from the door. This is because when the width of the opening is larger than the wavelength of the wave passing through the gap then it does not spread out much on the other side. But when the opening is smaller than the wavelength more diffraction occurs and the waves spread out greatly – with semicircular wavefront. The opening in this case functions as a localized source of sound.

Question. A and B could hear the music programme due to phenomenon named
(A) interference.
(B) scattering.
(C) diffraction.
(D) dispersion.

C

Question. Diffraction of sound takes place more when :
(A) sound is diffracted through an opening having width equal to the wavelength of the sound.
(B) sound is diffracted through an opening having width more than the wavelength of the sound.
(C) sound is diffracted through an opening having width less than the wavelength of the sound.
(D) diffraction of sound does not depend on the width of the opening.

C

Question. The minimum and maximum frequencies in the musical programme were 550 Hz and 10 kHz.
Which frequency was better audible around the pillar obstacle?
(A) 10 kHz
(B) 550 kHz
(C) Mid frequency
(D) The complete frequency range

A

Question. How the waveform will look like outside the door of the hall?
(A) Sound repeater
(B) Sound reflector
(C) Localized sound source
(D) None of the above

C

Question. Diffraction is more pronounced with ______ wavelengths.
(A) Longer
(B) Shorter
(C) fluctuating
(D) all

A

Assertion-Reason Questions

In the following questions, a statement of Assertion (A) is followed by a statement of Reason (R). Choose the correct answer out of the following choices.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false and R is also false.

Question. Assertion (A): No interference pattern is detected when two coherent sources are infinitely close to each other.
Reason (R): Fringe width is inversely proportional to separation between the slit.

B

Question. Assertion (A): Radiowaves can be polarised.
Reason (R): Radiowaves are transverse in nature.

A

Question. Assertion (A): The phase difference between any two points on a wavefront is zero.
Reason (R): Corresponding to a beam of parallel rays of light, the wavefronts are planes parallel to one another.

B

Question. Assertion (A): Thin films such as soap bubble or a thin layer of oil on water show beautiful colours when illuminated by white light.
Reason (R): It is due to interference of sun’s light reflected from upper and lower surfaces of the film.

A

Question. Assertion (A): Light is a wave phenomenon.
Reason (R): Light requires a material medium for propagation.

C

Question. Assertion (A): When the apparatus of Young’s double-slit experiment is brought in a liquid from air, the fringe width decrease.
Reason (R): The wavelength of light decreases in the liquid.

A

Question. Assertion (A): For identical coherent waves, the maximum intensity is four times the intensity due to each wave.
Reason (R): Intensity is proportional to the square of amplitude.

B

Question. Assertion (A): Skiers use air glasses.
Reason (R): Light reflected by snow is partially polarised.

B

Question. Assertion (A): Coloured spectrum is seen when we look through a muslin cloth.
Reason (R): Coloured spectrum is due to diffraction of white light passing through fine slits made by fine threads in the muslin cloth.