Answers Year 9 Science 7

1. REFLECTION FROM DIFFERENT SURFACES

a) Trace the position of the ray box and mirror and the ray paths. Label your diagram. What happens to the rays of light? All the rays are reflected at fixed angles.

b) Repeat using a piece of smooth aluminium foil held in place of the mirror. Once again trace the ray paths. What do you see? The aluminium foil reflects like a mirror. The light rays are not as bright as before and they appear distorted and fuzzy.

c) Explain the difference in the behaviour of the reflected light in terms of the surfaces used. • The light rays are again reflected in some apparent order, by the aluminium, although the emerging rays are more scattered. • White paper can also reflect light in straight lines. • In both cases, diffuse reflection occurs because of the rough surface used. The law of reflection holds for each reflected ray.

2. REFLECTION FROM A MIRROR

a) What is meant by "the angle of reflection"? The angle between the normal and the reflected ray.

EXPERIMENT ANGLE OF INCIDENCE ANGLE OF REFLECTION 1 30 30 2 45 45 Angle of Angle of 3 60 60 incidence reflection 4 76 76

b) What can you conclude from your table of results? Angle of incidence = Angle of reflection

07 Reflection Ans Page 1 of 2 EXERCISES

1. Explain why the light from an approaching car may dazzle you if the road is wet. Water on the road reflects light in straight lines since the surface is smooth.

2. Explain why you can see a pencil even though it is non-luminous. Light is reflected off the pencil into your eyes. Obviously if there is no light, in a dark room for example, then it is difficult to see the pencil.

3. A piece of white paper reflects a lot of light, yet you cannot see your own image in the paper. Explain. White paper has a rough surface and can reflect light in many different directions. This is called diffuse reflection because the light rays are scattered and can interfere with each other.

07 Reflection Ans Page 2 of 2