# Propagation of Light

Updated on January 9, 2013

This is a lab report from Physics 105 (Concepts of the Physical World) I took at GRCC in winter 2012.

We see things everyday and two conditions are necessary in order to see things. First, the light either natural sources of light such as sun, fire, moon, or star, or man-made sources of light such as incandescent light bulbs is needed. Second, a clear line of sight is required.

## How does light travel?

In this activity, I observed how light travels when connected light bulb was placed in the upright cylindrical comb that has teeth by placing it on a large sheet of white paper. Tracing the outline of the socket and comb on the paper indicates that light lines come out through the teeth of comb, which means the light is traveling in straight lines.

## Intensity VS. Distance

Does intensity of light change as distance from light to object changes? In this activity, I placed a light bulb, an object, and a white board and measured a distance from the light to the board.

D-distance from light to board, S-separation from light to object

Separation (cm)
D1 (cm) 1square
D2 (cm) 4 squares
D3 (cm) 9 squares
10
27
54
81
15
34
69
107
20
50
95
140
Area of Screen
Distance from light source (cm)

1 square
27
34
50
4 squares
54
69
95
9 squares
81
107
140

D2 is double of D1 and D3 is triple of D1. As distance from light to board gets further, the intensity of light decreases. When the light covers one quare, the intensity of light is good but when the light covers four suqares, the shadow gets dimmer.

## Conclusion

As we see the results from the activities, the distance and intensity are related to each other. As the distance from light gets further, the intensity of light decreases. In other words, parameter between light source and area of square increase, the brightness gets decrease.

23

1

2

24

26