81) Which of the following is not an example of refraction

A) bottom of the swimming pool with water appears to be raised
B) pencil placed in a tumbler of water appears to have a bent
C) lemon kept in a glass of water appears to be bigger than its size
D) appearance of our image in a plane mirror

82) The speed of light in benzene is 2×10⁸ m/s. Its refractive index is (speed of light in vacuum =3×10⁸m/s)

A) 0.66
B) 1
C) 1.5
D) 2

83) A light ray travels from air to glass with an angle of incidence of 45°. The possible angle of refraction is

A) 45°
B) 65°
C) 90°
D) 30°

84) According to laws of refraction, which of the following lie in the same plane

A) incident and refracted rays
B) incident ray, refracted ray and normal
C) incident ray and normal only
D) refracted ray and normal only

85) A focal plane is

A) parallel to the principal axis
B) perpendicular to the principal ais
C) at 45° to the principal axis
D) at 60° to the principal axis