# 'O' Level Standard questions on refraction

These questions are more taxing than GCSE standard questions. They are suitable for those taking 'O' Level or 'A' Level physics. You should always start by sketching a diagram and marking in angles and measurements that you are given or can calculate using simple geometry.

Q1.

(a) 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?

(b) If the angle of incidence of a ray of light falling on water is 65° and the refractive index of water is 1.33, calculate the angle of refraction.

(c) A ray of light is refracted as it travels out of glass into air. If that glass has a refractive index of 1.50 and the angle of incidence is 20°, what is the angle of refraction as it enters the air?

Q2.

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.

Q3.

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. Take the refractive index of the water as being 1.33.

At what angle to the horizontal will the ray travel after it leaves the water?

Q4.

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?

Take the refractive index of the water as being 1.33.

Q5.

Two faces of a glass prism with a refractive index of 1.50 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.

Q6.

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.

Questions relating to critical angle

Q7.

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

(b) The critical angle of diamond is 24°. What is its refractive index?

Q8.

A prism made of glass with a refractive index of 1.50 has two angles of 75° and one of 30°.

Determine whether a ray of light be reflected and/or refracted at one of the longer sides if it enters the prism normally onto

(a) the other longer side,

(b) the shorter side.

Questions relating to real and apparent depth

Q9.

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?

Q10.

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 if the refractive index of the glass is 1.50.