Physical Light

Name:_______________________ Class: F.___ Class No:_____

1. Light and sight We see an object when light from that object enters our eyes. Many rays from the object enter the eye at the same time. However, in diagrams, we only show two or some rays only.

A point gives out many rays but we usually draw _two___ rays to mark out the cone of rays from the point of the object reaching the eye (Fig 1a). To indicate that the eye sees the whole object, two cones of rays are drawn from the two _end____ of the object to the eye (Fig 1b).
|[pic] |[pic] |
|Fig 1a |Fig 1b |

To represent light from a distant object (e.g. the sun), we draw parallel rays. Light rays that are parallel to one another come from the same point on the distant object.

1.1 Figure 1c shows that light from a point on a near object reaches our eyes as _divergent _________ rays.

Fig 1c [pic]

1.2 Figure 1d shows that if the object moves away from us, the rays from the same point reaching our eyes become __ less __(less/more) divergent.

[pic]
Fig 1d

1.3 The rays reaching our eyes from a point of a distant object become __parallel_____ (Fig 1e).

[pic]
Fig 1e

2. Light rays and beams Objects that can give out light by themselves are called _luminous____ objects, for example, candles, the sun and light bulbs. Objects do not give out light by themselves are called __non-luminous_______ objects.

Light consists of narrow rays travelling in __straight________ lines.

A light beam is a stream of light. Figure 1f shows three kinds of light beams.

|[pic]