Refraction at plane and spherical surfaces; thin lens and lens-maker's formula — NEET & JEE Questions

Question 1 · difficulty L1 · recall

Snell's law for refraction is

• A. n1 cos i=n2 cos r
• B. n1 i=n2 r for all angles
• C. n1 sin i = n2 sin r
• D. n1/n2=sin r/sin i only when n1=n2

Question 2 · difficulty L1 · understanding

When light enters a medium of higher refractive index from a lower one, it generally bends

• A. away from the normal
• B. parallel to the interface for every angle
• C. without changing direction unless normal incidence
• D. toward the normal

Question 3 · difficulty L2 · understanding

The speed of light in a medium of refractive index n is

• A. c/n
• B. cn
• C. c n²
• D. c regardless of n

Question 4 · difficulty L2 · application

For a thin lens in air, the lens formula is

• A. 1/f=1/v+1/u
• B. 1/f = 1/v - 1/u
• C. f=u+v
• D. 1/f=u-v

Question 5 · difficulty L2 · understanding

When light travels from a rarer medium into a denser medium, it generally bends

• A. toward the normal
• B. away from the normal
• C. without any change in direction under all conditions
• D. parallel to the interface only

Question 6 · difficulty L3 · application

A converging lens has focal length 20 cm. Its power is

• A. +0.05 D
• B. -5 D
• C. +5 D
• D. +20 D

Question 7 · difficulty L3 · application

The lens-maker's formula for a thin lens in air shows that focal length depends on

• A. only lens thickness and not refractive index
• B. only object distance
• C. only aperture diameter
• D. refractive index and the curvatures of both surfaces

Question 8 · difficulty L3 · application

A thin converging lens has focal length 20 cm. What is its power?

• A. +2 D
• B. +5 D
• C. -5 D
• D. +20 D

Question 9 · difficulty L3 · application

For a thin lens in air, if object distance $u=-30$ cm and focal length $f=+15$ cm, the image distance using $1/f=1/v-1/u$ is

• A. +10 cm
• B. +15 cm
• C. +30 cm
• D. -30 cm

Question 10 · difficulty L4 · analysis

An object is placed at 2f in front of a thin converging lens. The image is formed

• A. at 2f on the other side, real and same size
• B. at f and highly magnified
• C. between lens and f, virtual
• D. at infinity