# MCQs for Physics Class 12 with Answers Chapter 10 Wave Optics

Students of class 12 Physics should refer to MCQ Questions Class 12 Physics Wave Optics with answers provided here which is an important chapter in Class 12 Physics NCERT textbook. These MCQ for Class 12 Physics with Answers have been prepared based on the latest CBSE and NCERT syllabus and examination guidelines for Class 12 Physics. The following MCQs can help you to practice and get better marks in the upcoming class 12 Physics examination

## Chapter 10 Wave Optics MCQ with Answers Class 12 Physics

MCQ Questions Class 12 Physics Wave Optics provided below have been prepared by expert teachers of grade 12. These objective questions with solutions are expected to come in the upcoming Standard 12 examinations. Learn the below provided MCQ questions to get better marks in examinations.

Question. A single slit diffraction pattern is obtained using a beam of red light. If the red light is replaced by the blue light, then the diffraction pattern
(a) remains unchanged
(b) becomes narrower
(d) will disappear

B

Question. Which one of the following phenomena is not explained by Huygens construction of wavefront?
(a) Refraction
(b) Reflection
(c) Diffraction
(d) Origin of spectra

D

Question. Which of the following does not support the wave nature of light?
(a) Interference
(b) Diffraction
(c) Polarisation
(d) Photoelectric effect.

D

Question. The deflection of light in a gravitational field was predicted first by
(a) Einstein
(b) Newton
(c) Max Planck
(d) Maxwell

B

Question. Huygens concept of wavelets is useful in
(a) explaining polarisation
(b) determining focal length of the lenses
(c) determining chromatic aberration
(d) geometrical reconstruction of a wavefront

D

Question. Interference is possible in
(a) light waves only
(b) sound waves only
(c) both light and sound waves
(d) neither light nor sound waves

C

Question. When a compact disc is illuminated by small source of white light, coloured bands are observed. This is due to
(a) dispersion
(b) diffraction
(c) interference
(d) reflection

Question. When light passing through rotating nicol is observed, no change in intensity is seen. What inference can be drawn ?
(a) The incident light is unpolarized.
(b) The incident light is circularly polarized.
(c) The incident light is unpolarized or circularly polarized.
(d) The incident light is unpolarized or circularly polarized or combination of both.

Question. The width of a slit is 0.012 mm. Monochromatic light is incident on it. The angular position of first bright line is 5.2º. The wavelength of incident light is [sin 5.2º = 0.0906].
(a) 6040 Å
(b) 4026 Å
(c) 5890 Å
(d) 7248 Å

D

Question. Light of wavelength 6.5 × 10–7 m is made incident on two slits 1 mm apart. The distance between third dark fringe and fifth bright fringe on a screen distant 1 m from the slits will be
(a) 0.325 mm
(b) 0.65 mm
(c) 1.625 mm
(d) 3.25 mm

C

Question. The path difference between two wavefronts emitted by coherent sources of wavelength 5460Å is 2.1 micron. The phase difference between the wavefronts at that point is
(a) 7.692
(b) 7.692 π
(c) 7.692/π
(d) 7.692/3π

B

Question. In Young’s double slit expt. the distance between two sources is 0.1 mm. The distance of the screen from the source is 20 cm. Wavelength of light used is 5460 Å. The angular position of the first dark fringe is
(a) 0.08º
(b) 0.16º
(c) 0.20º
(d) 0.32º

B

Question. The separation between successive fringes in a double slit arrangement is x. If the whole arrangement is dipped under water what will be the new fringe separation? [The wavelenght of light being used is 5000 Å]
(a) 1.5 x
(b) x
(c) 0.75 x
(d) 2 x

C

Question. Light of wavelength 6328 Å is incident normally on a slit having a width of 0.2 mm. The angular width of the central maximum measured from minimum to minimum of diffraction pattern on a screen 9.0 metres away will be about
(a) 0.36 degree
(b) 0.18 degree
(c) 0.72 degree
(d) 0.09 degree

A

Question. The wavelength of Ha line in hydrogen spectrum was found to be 6563 Å in the laboratory. If the wavelength of same line in the spectrum of a milky way is observed to be 6568Å, then recession velocity of milky way will be
(a) 105 m/s
(b) 1.05 × 106 m/s
(c) 10.5 × 106 m/s
(d) 0.105 × 106 m/s

B

Question. Two beams of light of intensity I1 and I2 interfere to give an interference pattern. If the ratio of maximum intensity to that of minimum intensity is 25/9, then I1/I2 is
(a) 5/3
(b) 4
(c) 81/625
(d) 16

D

Question. Light from two coherent sources of the same amplitude A and wavelength l illuminates the screen. The intensity of the central maximum is I0. If the sources were incoherent, the intensity at the same point will be
(a) 4I0
(b) 1I0
(c) I0
(d) I0/2

D

Question. When the light is incident at the polarizing angle on the transparent medium, then the completely polarized light is
(a) refracted light
(b) reflected light
(c) refracted and reflected light
(d) neither reflected nor refracted light

B

Question. In the phenomena of diffraction of light, when blue light is used in the experiment in spite of red light, then
(a) fringes will become narrower
(c) no change in fringe width
(d) None of these

A

Question. The wave fronts 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
(a) 0º
(b) 45º
(c) 90º
(d) cos–1(1/ √3)

D

Question. The Fraunhoffer ‘diffraction’ pattern of a single slit is formed in the focal plane of a lens of focal length 1 m. The width of slit is 0.3 mm. If third minimum is formed at a distance of 5 mm from central maximum, then wavelength of light will be
(a) 5000 Å
(b) 2500 Å
(c) 7500 Å
(d) 8500 Å

A

Question. Two points separated by a distance of 0.1 mm can just be inspected in a microscope, when light of wavelength 600Å is used. If the light of wavelength 4800 Å is used, the limit of resolution will become
(a) 0.80 mm
(b) 0.12 mm
(c) 0.10 mm
(d) 0.08 mm

D

Question. Two nicols are oriented with their principal planes making an angle of 60º. Then the percentage of incident unpolarised light which passes through the system is
(a) 100
(b) 50
(c) 12.5
(d) 37.5

C

Question. A beam of unpolarised light passes through a tourmaline crystal A and then through another such crystal B oriented so that the principal plane is parallel to A. The intensity of emergent light is I0. Now B is rotated by 45º about the ray. The emergent light will have intensity
(a) I0 / 2
(b) I0 / √2
(c) I0 √2
(d) 2I0

A

Question. The heavenly body is receding from earth, such that the fractional change in λ is 1, then its velocity is
(a) c
(b) 3c/5
(c) c/5
(d) 2c/5

A

Question. Fluorescent tubes give more light than a filament bulb of same power because
(a) the tube contains gas at low temperature
(b) ultraviolet light is converted into visible light by fluorescence
(c) light is diffused through the walls of the tube
(d) it produces more heat than bulb

B

Question. In young’s double-slit experiment, the intensity of light at a point on the screen where the path difference is l is λ, l being the wavelength of light used. The intensity at a point where the path difference is λ/4 l will be
(a) 1/4
(b) 1/2
(c) I
(d) zero

B

Question. In Young’s double slit experiment, the fringes are displaced by a distance x when a glass plate of refractive index 1.5 is introduced in the path of one of the beams. When this plate is replaced by another plate of the same thickness, the shift of fringes is (3/2) x. The refractive index of the second plate is
(a) 1.75
(b) 1.50
(c) 1.25
(d) 1.00

A

Question. A single slit Fraunhoffer diffraction pattern is formed with white light. For what wavelength of light the third secondary maximum in the diffraction pattern coincides with the second secondary maximum in the pattern for red light of wavelength 6500 Å?
(a) 4400 Å
(b) 4100 Å
(c) 4642.8 Å
(d) 9100 Å

C

Question. When the angle of incidence is 60° on the surface of a glass slab, it is found that the reflected ray is completely polarised. The velocity of light in glass is
(a) √2 X 103 ms-1
(b) √3 X 103 ms-1
(c) 2 X 103 ms-1
(d) 3 X 103 ms-1

B

Question. Consider a light beam incident from air to a glass slab at Brewster’s angle as shown in figure. 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.

(a) For a particular orientation, there shall be darkness as observed through the polaroid
(b) The intensity of light as seen through the polaroid shall be independent of the rotation
(c) The intensity of light as seen through the polaroid shall go through a minimum but not zero for two orientations of the polaroid
(d) The intensity of light as seen through the polaroid shall go through a minimum for four orientations of the polaroid

C

Question. Consider sunlight incident on a slit of width 104 Å. The image seen through the slit shall
(a) be a fine sharp slit white in colour at the centre
(b) a bright slit white at the centre diffusing to zero intensities at the edges
(c) a bright slit white at the centre diffusing to regions of different colours
(d) only be a diffused slit white in colour

A

Question. Two waves having the intensities in the ratio of 9 : 1 produce interference. The ratio of maximum to minimum intensity is
(a) 10 : 8
(b) 9 : 1
(c) 4 : 1
(d) 2 : 1

C

Question. In a Young’s double-slit experiment, the source S and two slits A and B are horizontal, with slit A above slit B. The fringes are observed on a vertical screen K. The optical path length from S to B is increased very slightly (by introducing a transparent material of higher refractive index) and optical path length from S to A is not changed. As a result, the fringe system on K moves
(a) vertically downwards slightly
(b) vertically upwards slightly
(c) horizontally slightly to the left
(d) horizontally slightly to the right

A

Question. Four independent waves are expressed as
(i) y1 a1 = sin t ϖt
(ii) y2 a2 sin 2 ϖt
(iii) y3 = a3 cos t ϖt and
(iv) y4 = a4  sin ( ϖt +π/3)
The interference is possible between
(a) (i) and (iii)
(b) (i) and (iv)
(c) (iii) and (iv)
(d) not possible at all

A

Question. In a Young’s double-slit experiment the fringe width is found to be 0.4 mm. If the whole apparatus is dipped in water of refractive index 4/3, without disturbing the arrangement, the new fringe width will be
(a) 0.30 mm
(b) 0.40 mm
(c) 0.53 mm
(d) 0.2 mm

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. In Young’s double-slit experiment, the distance between the slit sources and the screen is 1 m. If the distance between the slits is 2 mm and the wavelength of light used is 600 nm, the fringe width is
(a) 3 mm
(b) 0.3 mm
(c) 6 mm
(d) 0.6 mm

D

Question. Figure shows a standard two slit arrangement with slits S1, S2. P1, P2 are the two minima points on either side of P.

At P2 on the screen, there is a hole and behind P2 is a second 2- slit arrangement with slits S3, 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. An astronomical refracting telescope will have large angular magnification and high angular resolution, when it has an objective lens of
(a) small focal length and large diameter
(b) large focal length and small diameter
(c) large focal length and large diameter
(d) small focal length and small diameter

C

Question. The Young’s double-slit experiment is performed with blue and green lights of wavelengths 4360 Å and 5460 Å respectively. If x is the distance of 4th maxima from the central one, then

C

Question. A ray of light is incident on the surface of a glass plate at an angle of incidence equal to Brewsters angle φ. If n represents the refractive index of glass with respect to air, then the angle between the reflected and refracted rays is
(a) 90 + φ
(b) sin–1 (n cosz)
(c) 90°
(d) 90° – sin1 (sinφ/n)

C

Question. Consider the diffraction pattern for a small pinhole. As the size of the hole is increased
(a) the size decreases
(b) the intensity increases
(c) the size increases
(d) the intensity decreases

A, B

Question. The angular resolution of a 10 cm diameter telescope at a-wavelength 500 nm is of the order of

B

Question. Unpolarised light is incident from air on a plane surface of a material of refractive index n. At a particular angle of incidence i, it is found that the reflected and refracted rays are perpendicular to each other. Which of the following options is correct for this situation?
(a) Reflected light is polarised with its electric vector parallel to the plane of incidence
(b) Reflected light is polarised with its electric vector perpendicular to the plane of incidence
(c) i = sin–1 (1/n)
(d) i = tan–1 (1/n)

A

Question. For light diverging from a point source
(a) the wavefront is spherical.
(b) the intensity decreases in proportion to the distance squared.
(c) the wavefront is parabolic.
(d) the intensity at the wavefront does not depend on the distance.

A, B

Question. In Young’s experiment, monochromatic light is used to illuminate the slits A and B. Interference fringes are observed on a screen placed in front of the slits. Now if a thin glass plate is placed in the path of the beam coming from A, then

(a) the fringes will disappear
(b) the fringe width will increase
(c) the fringe width will decrease
(d) there will be no change in the fringe width

D

Question. A telescope has an objective lens of 10 cm diameter and is situated at a distance of 1 km from two objects. The minimum distance between these objects that can be resolved by the telescope, when the mean wavelength of light is 5000 Å is of the order of
(a) 5 mm
(b) 5 cm
(c) 2.5 m
(d) 5 m

A

Question. Which of the following phenomenon cannot take place with longitudinal waves (e.g., sound waves)?
(a) reflection
(b) interference
(c) diffraction
(d) polarisation

D

Question. In Young’s double slit experiment the separation d between the slits is 2 mm, the wavelength λ of the light used is 5896 Å and distance D between the screen and slits is 100 cm. It is found that the angular width of the fringes is 0.20°. To increase the fringe angular width to 0.21° (with same λ and D) the separation between the slits needs to be changed to
(a) 1.8 mm
(b) 1.9 mm
(c) 2.1 mm
(d) 1.7 mm

B

#### Fill in the Blanks

Question. A beam of light is incident normally upon a polariser and the intensity of emergent beam is IO. The intensity of the emergent beam is found to be unchanged when the polariser is rotated about an axis perpendicular to the pass axis. Incident beam is _________________ in nature.

unpolarised

Question. In interference and _________________, the light energy is redistributed, increases in one region and decreases in other.

diffraction

Question. In Young’s double slit experiment, the fringe width is given by _________________.

β = Dλ/d

Question. Fringe width is different as separation between two consecutive _________________ or _________________.

maxima, minima

Question. The tangent of angle of polarization as light ray travels from air to glass is equal to the refractive index. This law is called as _________________.

Brewster’s law

Question. _________________ of light occurs when size of the obstacle of aperture is comparable to the wavelength of light.

Diffraction

Question. The value of Brewster angle depends on the nature of the transparent refracting medium and the _________________ of light used.

wavelength

Question. At polarising angle the refracted and reflected rays are _________________ to each other.

perpendicular

Question Continuous locus of oscillation with constant phase is called as _________________.

wave-front

Question. The phase difference between two waves in _________________ interference is given as an even multiple of π.