OAT Physics: Optics and Waves 2

Question 1

A converging lens has a focal length of 20 cm. An object is placed 30 cm from the lens. Where is the image formed?

Accepted Answer

60 cm on the opposite side of the object

Answer

Using 1/f = 1/do + 1/di: 1/20 = 1/30 + 1/di → di = 60 cm on the opposite side (real image).

Question 2

Which phenomenon explains why the sky appears blue?

Accepted Answer

Rayleigh scattering of shorter wavelengths

Answer

Rayleigh scattering preferentially scatters shorter (blue) wavelengths of sunlight in all directions, making the sky appear blue.

Question 3

Two waves with equal amplitude A are superimposed. If they are exactly out of phase (180°), the resultant amplitude is:

Accepted Answer

0

Answer

Destructive interference occurs when waves are 180° out of phase, causing complete cancellation and a resultant amplitude of zero.

Question 4

The critical angle for total internal reflection at a glass-air interface is 42°. What is the index of refraction of the glass?

Accepted Answer

1.49

Answer

At critical angle: sin(θc) = n_air/n_glass → n_glass = 1/sin(42°) ≈ 1.49.

Question 5

Which type of wave requires a medium to propagate?

Accepted Answer

Sound waves

Answer

Sound waves are mechanical waves that require a medium (solid, liquid, or gas) to propagate, unlike electromagnetic waves.

OAT - Optometry Admission Test Practice Test