Identify the correct statements.
(A) A concave mirror is preferred over a plane mirror for the purpose of shaving.
(B) The absolute refractive index of a medium can be less than unity.
(C) Snell's law gives the relative refractive index of a medium.
(D) When a convex lens is placed inside a transparent medium of refractive index greater than that of its own material, it behaves as a diverging lens.
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → (A), (C) and (D) only
(A) A concave mirror is preferred over a plane mirror for the purpose of shaving. — Correct. When the face is within the focal length, a concave mirror forms an enlarged, erect, virtual image, which shows the skin clearly; a plane mirror gives an image of the same size.
(B) The absolute refractive index of a medium can be less than unity. — Incorrect. The absolute refractive index is \( n = c/v \), and light cannot travel faster than \( c \) in a material medium, so \( n \) is at least 1.
(C) Snell's law gives the relative refractive index of a medium. — Correct. \( \sin i/\sin r = n_{21} \) is the refractive index of the second medium with respect to the first, that is, the relative refractive index.
(D) When a convex lens is placed inside a transparent medium of refractive index greater than that of its own material, it behaves as a diverging lens. — Correct. The focal length depends on \( (n_{\mathrm{lens}}/n_{\mathrm{medium}} - 1) \), which becomes negative when the medium has the larger index, so the convex lens diverges the light.
So the correct statements are (A), (C) and (D), which is Option (3).