Refraction at plane and spherical surfaces; thin lens and lens-maker's formula — practice 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 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 6 · 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 7 · 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

Question 8 · difficulty L4 · analysis

A ray passes through a parallel-sided glass slab and emerges into the original medium. The emergent ray is

• A. always perpendicular to the incident ray
• B. parallel to the incident ray but laterally displaced
• C. convergent toward a focus
• D. antiparallel to the incident ray

Question 9 · difficulty L5 · analysis

A biconvex glass lens is immersed in a liquid whose refractive index equals that of the glass. Its optical power becomes

• A. larger positive
• B. large negative
• C. approximately zero
• D. twice its air value

Question 10 · difficulty L5 · analysis

A spherical refracting surface separates media n1 and n2. Which feature distinguishes it from a thin lens?

• A. It cannot form images
• B. It obeys reflection rather than refraction
• C. Its behaviour is independent of refractive indices
• D. Refraction occurs at one curved interface rather than two separated refracting surfaces