Refraction
Questions
Unless
otherwise stated, take: Refractive index of glass = 3/2, of water =
4/3.
(Examples 20 to 24 are particularly suitable for graphical methods).


ANSWERS

20 
A
ray of light falls on a glass block and the angle of incidence is
45°. If the angle of refraction is 30°, what is the refractive
index of glass?

1.4

21 
If the angle of incidence of a ray of light falling on water is
65°, what is the angle of refraction? 
43°

22 
A glass block has two parallel sides which are 5.0 cm apart and
the angle of incidence of a ray of light falling on one of the two
parallel sides is 50°. Find by drawing or calculation the perpendicular
distance between the ray entering the block and the ray leaving
the block. 
1.9
cm

23 
A ray of light is refracted from glass into the air. If the angle
of incidence is 20°, what is the angle of refraction? 
31°

24 
A diver is working under water and a ray of light from his lamp
strikes the surface of the water at an angle of 55° to the horizontal.
At what angle to the horizontal will the ray travel after it leaves
the water? 
40°

25 
A fish under water looks upwards and sees the setting sun. What
is the angle between the horizontal and the ray of light which is
entering the fish's eye? 
41°

26 
Two faces of a glass prism have an angle of 40° between them.
A ray of light is incident on one of the faces at an angle of 45°.
Trace the path of the ray through the prism and find the angle between
the direction of the ray entering the prism and the direction of
the ray leaving the prism. 
23°

27 
A glass prism has three angles of 60°. A ray of light falls
on one of the faces and the angle of incidence is 49°. The ray
is refracted and now travels parallel to the second face. When it
reaches the third face it is refracted again and emerges from the
prism. Find (a) the refractive index of the glass of the prism,
(b) the angle between the ray entering the prism and the ray leaving
the prism. 
1.5
38°

28

Taking
the refractive index of water as 4/3, what is the critical angle
for water?

48°

29

The
critical angle of diamond is 24°. What is its refractive index? 
2.5

30 
A prism of glass has two angles of 75° and one of 30°. Will
a ray of light be reflected and/or refracted at one of the longer
sides if it enters the prism normally to (a) the other longer side,
(b) the shorter side? 
(a)
both
(b)
reflected only

31 
A stone lies at the bottom of a lake 8.0 m deep. To an observer
directly above the stone it only appears to be 6.0 m below the surface.
What is the refractive index of water? 
4/3
(1.33)

32

A
rectangular glass block 12 cm thick is placed over an ink mark on
a sheet of paper. Find the distance the ink mark is apparently raised. 
4.0
cm
