NEET Physics Wave Optics MCQs Set A

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

Answer: be a fine sharp slit white in colour at the centre

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 no interference fringes

b) there shall be an interference pattern for red mixing with one for blue

c) there shall be alternate interference patterns of red and blue

d) None of these

Answer:  there shall be no interference fringes

Question:  In Young’s double slit experiment, we get 10 fringes in the field of view of monochromatic light of wavelength 4000Å. If we use monochromatic light of wavelength 5000Å, then the number of fringes obtained in the same field of view is

a) 8

b) 10

c) 50

d) 40

Answer: 8

Question: Assertion : In Young’s double slit experiment if wavelength of incident monochromatic light is just doubled, number of bright fringe on the screen will increase.
Reason : Maximum number of bright fringe on the screen is directly proportional to the wavelength of light used.

a) Assertion is incorrect, reason is correct.

b) Assertion is correct, reason is incorrect

c) Assertion is correct, reason is correct; reason is not acorrect explanation for assertion

d) Assertion is correct, reason is correct; reason is a correct explanation for assertion

Answer:  Assertion is incorrect, reason is correct.

Question:  On a hot summer night, the refractive index of air is smallest near the ground and increases with height from the ground. When a light beam is directed horizontally, the Huygens' principle leads us to conclude that as it travels, the light  beam :

a) bends upwards

b) goes horizontally without any deflection

c) becomes narrower

d) bends downwards

Answer: bends upwards

Question:  Calculate the wavelength of light used in an interference experiment from the following data : Fringe width = 0.03 cm. Distance between the slits and eyepiece through which the interference pattern is observed is 1m. Distance between the images of the virtual source when a convex lens of focal length 16 cm is used at a distance of 80 cm from the eyepiece is 0.8 cm.

a) 6000 Å

b) 600 cm

c) 0.0006 m

d) 0.0006 Å

Answer: 6000 Å

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) 4642.8 Å

b) 9100 Å

c) 4100 Å

d) 4400 Å

Answer: 4642.8 Å

Question: Young's double slit experment is first performed in air and then in a medium other than air. It is found that 8th bright fringe in the medium lies where 5th dark fringe lies in air. The refractive index of the medium is nearly

a) 1.78

b) 1.25

c) 1.69

d) 1.59

Answer:  1.78