It's colder in winter

Find out how the illumination of a surface changes as the angle between the rays from the light source and the surface decreases. Use the light ray to explain the phenomenon.

How to study it

Place a screen in front of the parallel beam formed by the three-slit system. Now rotate the screen to different angles with respect to the direction of the rays. What do you notice?

Light falls on the screen at different angles

How to conduct the test

In this experiment, we can see how the illuminance of a surface changes as the angle between the rays from the light source and the surface decreases.

What can be deduced from it

So: if the paper is not perpendicular to the light, the brightness of the light beam on it decreases (to zero if the paper is facing the light source). In the experiment, we see this as an increase in the distance between the rays on the paper. This, in turn, means that proportionately less light energy is incident on each unit area.

It is quite easy to see the parallel here with the way in which, at our latitude, when the sun is just above the horizon in winter, light is 'spread out' over a very large surface area .... and gets cold.