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