Which of the following statements are correct?
A. The angle at minimum deviation of a prism is greater for violet light than that for red light.
B. The purpose of microscopes and telescopes is to increase the visual angle.
C. For the diffraction to take place the size of aperture or of the obstacle should be comparable to the wavelength of light.
D. The light scattered in the direction of the incident light is always plane polarised.
E. The source and its virtual image can behave as coherent sources.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → A, B, C, E Only
(A) The angle at minimum deviation of a prism is greater for violet light than that for red light. — Correct. For a thin prism \( \delta_m = (\mu - 1)A \). Glass has a larger refractive index for violet than for red, so violet is deviated more.
(B) The purpose of microscopes and telescopes is to increase the visual angle. — Correct. Both instruments form an image that subtends a larger angle at the eye than the object does.
(C) For the diffraction to take place the size of aperture or of the obstacle should be comparable to the wavelength of light. — Correct. The spreading of light is noticeable only when the opening or obstacle is comparable to the wavelength.
(D) The light scattered in the direction of the incident light is always plane polarised. — Incorrect. Scattered light is plane polarised only perpendicular (at \( 90^\circ \)) to the incident light; light scattered forward is unpolarised.
(E) The source and its virtual image can behave as coherent sources. — Correct. The image is formed from the source's own light, so the two have a constant phase difference. Lloyd's mirror uses a source and its virtual image to produce interference fringes.