CBSE Class 12 Physics Wave Optics MCQs Set 06

Question: Two sources of light of wavelength 2500 Å and 3500 Å are used in Young’s double slit experiment simultaneously. Which orders of fringes of two wavelength patterns coincide?
(a) 3rd order of 1st source and 5^th of the 2^nd
(b) 7th order of 1st and 5^th order of 2nd
(c) 5th order of 1st and 3^rd order of 2nd
(d) 5th order of 1st and 7th order of 2nd 
Answer: b

Question: In Young’s double slit experiment the distance d between the slits S₁ and S₂ is 1 mm.
What should the width of each slit be so as to obtain 10 maxima of the double slit pattern within the central maximum of the single slit pattern?
(a) 0.9 mm
(b) 0.8 mm
(c) 0.2 mm
(d) 0.6 mm 
Answer: c

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 thiscase
(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
Answer: c

Question: 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
Answer: c

Question: The idea of secondary wavelets for the propagation of a wave was first given by
(a) Newton
(b) Huygens
(c) Maxwell
(d) Fresnel 
Answer: b

Question:The phenomena which is not explained by Huygens construction of wavefront
(a) reflection
(b) diffraction
(c) refraction
(d) origin of spectra 
Answer: d

Question: Yellow light of wavelength 6000 Å produces fringes of width 0.8 mm in Young’s double slit experiment. If the source is replaced by another monochromatic source of wavelength 7500 Å and the separation between the slits is doubled then the fringe width becomes
(a) 0.1 mm
(b) 0.5 mm
(c) 4.3 mm
(d) 1 mm 
Answer: b

Question: A narrow slit of width 2 mm is illuminated by monochromatic light of wavelength 500 nm.
The distance between the first minima on either side on a screen at a distance of 1 m is
(a) 5 mm
(b) 0.5 mm
(c) 1 mm
(d) 10 mm 
Answer: b

Question: Light from two coherent sources of the same amplitude A and wavelength λ 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) 2I₀
(c) I₀
(d) I₀/2
Answer: d

Question: For what distance is ray optics a good approximation when the aperture is 4 mm wide and the wavelength is 500 nm?
(a) 22 m
(b) 32 m
(c) 42 m
(d) 52 m 
Answer: b

Question: Wavefront is the locus of all points, where the particles of the medium vibrate with the same
(a) phase
(b) amplitude
(c) frequency
(d) period 
Answer: a

Question: In a Young’s double slit experiment, the angular width of a fringe formed on a distant screen is 1°. The slit separation is 0.01 mm. The wavelength of the light is
(a) 0.174 nm
(b) 0.174 Å
(c) 0.174 μm
(d) 0.174 × 10^–4 m 
Answer: c

Question: Young’s experiment is performed with light of wavelength 6000 Å wherein 16 fringes occupy a certain region on the screen.
If 24 fringes occupy the same region with another light, of wavelength λ, then λ, is
(a) 6000 Å
(b) 4500 Å
(c) 5000 Å
(d) 4000 Å 
Answer: d

 Question: A slit of width d is illuminated by white light.
The first minimum for red light (l = 6500 Å) will fall at q = 30° when d will be
(a) 3200 Å
(b) 6.5 × 10^–4 mm
(c) 1.3 micron
(d) 2.6 × 10^–4 cm C
Answer: c

Assertion & Reasoning Based MCQs
two statements are given-one labelled Assertion (A) and the other labelled Reason (R).
Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
(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) : Interference obeys the law of conservation of energy.
Reason (R) : The energy is redistributed in case of interference.
Answer: a

Question: Assertion (A) : We cannot get diffraction pattern from a wide slit illuminated by monochromatic light.
Reason (R) : In diffraction pattern, all the bright bands are not of the same intensity.
Answer: b

Question: Assertion (A) : One of the condition for interference is that the two source should be very narrow.
Reason (R) : One broad source is equal to large number of narrow sources.
Answer: a

Question: Assertion (A) : The maximum intensity in interference pattern is four times the intensity due to each slit.
Reason (R): Intensity is directly proportional to square of amplitude.
Answer: b

Question: Assertion (A) : When a light wave travels from a rarer to a denser medium, it loses speed.
The reduction in speed imply a reduction in energy carried by the light wave.
Reason (R) : The energy of a wave is proportional to velocity of wave.
Answer: d

Very Short Answer Type Questions  

Question: What is the shape of the wavefront on earth for sunlight?
Answer : There would be spherical wave front on earth for sunlight which is treated as point source, but radius is very large as compared to radius of earth, so it is almost a plane wavefront

Question: Why is the diffraction of sound waves more evident in daily experience than that of light wave?
Answer : The diffraction effect is more pronounce if the size of the aperture or the obstacle is of the order of wavelength of wave.
As wavelength of light (≃ 10^–6 m) is much more smaller than size of object around us so diffraction of light is not easily seen but sound wave has large wavelength (15 mm < λ< 15 m), they get easily diffracted by objects around us.

Question:If one of the slits in Young’s double slit experiment is fully closed, the new pattern has ______ central
maximum in angular size. 
Answer :In young’s double slit experiment, if one slit is fully closed, the new pattern has larger central maximum in angular size.