## Interference and Diffraction MCQ Questions and Answers Quiz

31. If you look perpendicular at thin film and move yourself away from the film (staying perpendicular to the film), you will notice

1. Reflected light becomes brighter and brighter
2. Reflected light becomes darker and darker
3. Reflected light alternates between darker and brighter
4. None of the Above

32. In a longitudinal wave

1. The particles move parallel to the direction of the wave motion.
2. The particles move perpendicular to the direction of the wave motion.
3. Energy causes the particles to move forward with the wave.
4. Energy is propagated by crests and troughs.

33. In a Youngs double-slit experiment the center of a bright fringe occurs wherever waves from the slits differ in the distance they travel by a multiple of

1. a fourth of a wavelength
2. a half a wavelength
3. a wavelength
4. three-fourths of a wavelength

34. In case of thin film of non-uniform thickness, when illuminated with white light, the film appears colored. This is due to change of what factor?

1. Conditions for path difference at different points of film
2. Change in optical path difference at different points of film
3. Thickness of film is different at different points of film
4. All of above

35. In diffraction Fraunhofer diffraction pattern due to single slit central maxima is formed at center because

1. Lens focuses all the diffracted rays at the centre of the slit
2. Slit focuses all the diffracted rays at the centre of the slit
3. Light rays focused at the centre of the screen undergo constructive interference
4. Slit and lens both combined focuses the rays at the centre of the slit

36. In diffraction pattern of monochromatic light the bright bands formed are

1. of uniform intensity
2. of non-uniform intensity
3. of uniform width
4. is of different colors

37. In Fraunhofer diffraction pattern for single slit, a central maximum is obtained when angle of diffraction q is equal to zero. What it actually indicates?

1. All the diffracted rays are parallel and focused by slit at a single point on screen
2. All the diffracted rays are perpendicular and focused by slit at a single point on screen
3. The rays are diffracted by the slit in all the directions
4. The rays are reflected by the slit

38. In Fraunhofer diffraction wave front used is

1. Spherical
2. Circular
3. Plane
4. Conical

39. In Fraunhofer diffraction, the incident wave front should be

1. elliptical
2. Plane
3. Spherical
4. Cylindrical

40. In Fresnel diffraction

1. source of light is kept at infinite distance from the aperture
2. source of light is kept at finite distance from the aperture
3. Convex lens used
4. aperture width is selected so that it can acts as a point source
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