Class 12 Physics MCQ Questions of Wave Optics with Answers available free on the Sarthaks eConnect website. We have provided MCQ Questions for Class 12 Physics with Answers to help students understand the concept very well. Check the below Class 12 Physics MCQ Questions of Wave Optics with Answers. The Class 12 MCQ Questions are prepared after analyzing the syllabus prescribed by the NCERT and the previous year’s question papers.

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Practice MCQ Question for Class 12 Physics chapter-wise

1. Resolving power of telescope can be increased by increasing

(a) the wavelength
(b) the diameter of objective
(c) the diameter of eyepiece
(d) the focal length of eyepiece

2.  Polarisation of light proves

(a) corpuscular nature of light
(b) quantum nature of light
(c) transverse wave nature of light
(d) longitudinal wave nature of light

3. The wavefront due to a source situated at infinity is

(a) spherical
(b) cylindrical
(c) planar
(d) circular

4. A laser beam is coherent because it contains

(a) waves of several wavelengths
(b) incoherent waves of a single wavelength
(c) coherent waves of several wavelengths
(d) coherent waves of a single wavelength

5. When exposed to sunlight, thin films of oil on water of ten exhibit brilliant colours due to the phenomenon of

(a) interference
(b) diffraction
(c) dispersion
(d) polarisation

6. When compact disk is illuminated by a source of white light, coloured lines are observed. This is due to

(a) dispersion
(b) diffraction
(c) interference
(d) refraction

7. When unpolarised light beam is incident from air onto glass (n = 1.5) at the polarising angle.

(a) Reflected beam is polarised completely
(b) Reflected and refracted beams are partially polarised
(c) Refracted beam is plane polarised
(d) Whole beam of light is refracted

8. The phenomenon of interference is based on

(a) conservation of momentum
(b) conservation of energy
(c) conservation of momentum and energy
(d) quantum nature of light

9. In Young’s double slit experiment, if the monochromatic source of yellow light is replaced by red light, the fringe width

(a) increases
(b) decreases
(c) remains unchanged
(d) the fringes disappear

10. The idea of secondary wavelets for the. propagation of a wave was first given by

(a) Newton
(b) Huygens
(c) Maxwell
(d) Fresnel

11. Light propagates rectilinearly, due to

(a) wave nature
(b) wavelengths
(c) velocity
(d) frequency

12. The refractive index of glass is 1.5 for light waves of X = 6000 A in vacuum. Its wavelength in glass is

(a) 2000 Å
(b) 4000 Å
(c) 1000 Å
(d) 3000 Å

13. The phenomena which is not explained by Huygen’s construction of wavefront

(a) reflection
(b) diffraction
(c) refraction
(d) origin of spectra

14. When interference of light takes place

(a) energy is created in the region of maximum intensity
(b) energy is destroyed in the region of maximum intensity
(c) conservation of energy holds good and energy is redistributed
(d) conservation of energy does not hold good

15. To observe diffraction, the size of the obstacle

(a) should beX/2, where X is the wavelength
(b) should be of the order of wavelength
(c) has no relation to wavelength
(d) should be much larger than the wavelength

16. A single slit diffraction pattern is obtained using a beam of red light What happened the red light is replaced by the blue light?

(a) There is no change in diffraction pattern
(b) Diffraction fringes become narrower and crowded
(d) Diffraction fringes become broader and farther apart
(d) The diffraction pattern disappear

17. When a polaroid is rotated, the intensity of light varies but never reduces to zero. It shows that the incident light is:

(a) unpolarised
(b) completely plane polarised
(c) partially plane polarised
(d) None of the above

18. Two sources of light are said to be coherent when both give out light waves of the same:

(a) amplitude and phase
(b) intensity and wavelength
(c) speed
(d) wavelength and a constant phase difference

19. The theory of expanding universe is confirmed by the observation of the spectral lines of the star, which shows :

(a) green shift
(b) red shift
(c) violet shift
(d) yellow shift

20. Polaroid glasses is used in sun glasses because :

(a) It reduces the light intensity to half on account of polarization
(b) It is fashionable
(c) It has good colour
(d) It is cheaper

21. In Young’s double slit experiment, the central point on the screen is:

(a) bright
(b) dark
(c) first bright and later dark
(d) first dark and later bright

22. A person cannot see object clearly beyond 50 cm. The power of the lens to correct his vision is :

(a) +0.5 dioptre
(b) -0.5 dioptre
(c) -2 dioptre
(d) +2 dioptre

23. A young’s double slit experiment uses a monochromatic source. The shape of interference fringes formed on a screen is :

(a) parabola
(b) straight line
(c) circle
(d) hyperbola

24. Intensity of light depends on

(a) amplitude 
(b) frequency
(c) wavelength 
(d) velocity

25. Instead of using two slits, if we use two separate identical sodium lamps in Young’s experiment, which of the following will occur?

(a) General illumination
(b) Widely separate interference
(c) Very bright maxima
(d) Very dark minima

Answer :

1. Answer : (b) the diameter of objective

Explanation: As the wavelength of the incident light is fixed, we can increase the resolving power by increasing the diameter of the objective lens. Hence, in order to increase the resolving power, the diameter of the objective lens can be increased.

2. Answer : (c) transverse wave nature of light

Explanation: Polarisation explain the wave nature of light, as light wave are polarised in a particular plane. The longitudinal waves cannot to be polarised. So, transverse wave can only be polarised. Hence, polarisation of light proves the transverse nature of light.

3. Answer : (c) 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.

4. Answer : (d) coherent waves of a single wavelength

Explanation: LASER is the short form of Light Amplification by Stimulated Emission of Radiation. Laser beam is intense, monochromatic (that is of the single wavelength) collimated and highly coherent.

5. Answer : (a) interference

Explanation: The colour in the oil film is formed due to Interference of sunlight where the colour of the film will depend upon the thickness and the angle of inclination.

6. Answer : (b) diffraction

Explanation: The fine rulings, each 0,.5μm wide, on a compact disc function as a diffraction grating. When a small source of white light illuminates a disc, the light is diffracted from the rulings.

7. Answer : (b) Reflected and refracted beams are partially polarised

Explanation: If unpolarised light is incident at polarising angle, then reflected light is completely, i.e, 100% polarised.

8. Answer : (b) conservation of energy

Explanation: The phenomenon of interference is based on conservation of energy. The energy is distributed in the interference phenomena in such a way that the strength of the resultant wave is maximal at certain spots and minimum at others, the phenomenon of interference is based on energy conservation.

9. Answer : (a) increases

Explanation: Using the relation for fringe width β = Dλ/2d hence, β∝λ Since, λ_red >λ_yellow.  Therefore using the red light in place of yellow light, fringe width will increase.

10. Answer : (b) Huygens

Explanation: Huygens principle states that every point on a wavefront is a source of secondary wavelets. These wavelets spread out in the forward direction, at the same speed as the source wave. The new wavefront is a line tangent to all of the wavelets.

11. Answer : (a) wave nature

Explanation: Light propagates rectilinearly. But it can take a slight turn at obstacles. This property of light is due to its wave nature.

12. Answer : (b) 4000 Å

Explanation: 

\(\mu=\frac{c}{v}=\frac{\lambda_v}{\lambda_g}\)

\(\therefore\lambda_g=\frac{\lambda_u}{\mu}\)

\(=\frac{6000}{1.5}\)

= 4000 Å

13. Answer : (d) origin of spectra

Explanation: The Huygen's construction of wavefront does not explain the phenomena of origin of spectra.

14. Answer : (c) conservation of energy holds good and energy is redistributed

Explanation: Interference is a phenomenon in which two waves superimpose to form a resultant wave of greater of lower amplitude. There is no loss of energy during interference. It is simply redistributed.

15. Answer : (b) should be of the order of wavelength

Explanation: To observed diffraction, the size of the obstacle should be of the order of wavelength. i.e. λ = d.

16. Answer : (b) Diffraction fringes become narrower and crowded

Explanation: As λ_blue < λ_red, and width of diffraction bands is directly proportional to λ, therefore diffraction bands become narrower and crowded.

17. Answer : (c) partially plane polarised

Explanation: Polaroid cuts off plane polarised light for one orientation.

18. Answer : (d) wavelength and a constant phase difference

Explanation: As these sources are from a single original source, their frequency or wavelength will be the same. Thus, two sources of light are said to be coherent, when they give light waves of same wavelength and constant phase difference.

19. Answer : (b) red shift

Explanation: bservations show that the spectral lines of distant galaxies are redshifted, and that their recession velocities are proportional to their distances from us, a relationship known as Hubble's law.

20. Answer : (a) It reduces the light intensity to half on account of polarization

Explanation: When light is reflected from flat surfaces becomes polarised, meaning travels in a uniform direction. To overcome this, polarised lenses are used.

21. Answer : (a) bright

Explanation: In the normal adjustment of YDSE, Path difference between the waves at central location is always zero. So maxima is obtained at central position. Central point on the screen is bright.

22. Answer : (c) -2 dioptre

Explanation: Here v = - 50 mm, u = ∞

Hence using 1/f =1/v=1/u we find f = - 50 cm = 0.50 m

So power of the lens is P = 1/ −0.50m =−2D

23. Answer : (b) straight line

Explanation: Monochromatic means light with single wavelength .Hence shape of interference fringes formed on the screen is straight line. If instead of double slit experiment double hole experiment was given shape would have been hyperbolla.

24. Answer :(a) amplitude 

Explanation: Light is an electromagnetic wave. its intensity will depend on the amplitude of the wave. The amplitude of light is measured in volts per meter in one direction perpendicular to its propagation direction.

25. Answer : (a) General illumination

Explanation: The superimposing waves will not be in constant phase. This leads to general illumination.

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