Re: Area of illumination

I have tried to create some diagrams of the experiment you are doing for the area of illumination:

As you move the graph paper further from the black paper with the square hole, the area illuminated got larger:

There are a couple of things you should note in your experiment:

(1) As you moved the graph paper further away from the light, the area (the number of square centimeters on the graph paper) that were illuminated should have increased with the SQUARE of the distance it was moved away.

If you graphed the Area of Illumination against the distance the graph paper was away from the light source, the graph should have looked something like:

This is because both the distance illuminated in the horizontal, x -axis, and the vertical, y-axis, were increasing -- since Area is x times y, the Area illuminated went up with the distance SQUARED!

(2) Also, as you moved the graph paper further away from the light, the light intensity of the area illuminated on the graph paper should have gotten much weaker -- and this should have dropped off very rapidly.

If you graphed the Power of the light (light energy per unit area), against the distance the graph paper was away from the light source, the graph would look like:

This relates to some important equations in physics, referred to as "the inverse square laws".

Because the total energy from the light source is constant (energy can neither be created nor destroyed), and the area is going up as the square of the distance (as discussed above), then the energy per unit area, Power, is going down as the inverse of the square of the distance.

This inverse square law shows up in all sorts of real life situations -- such as why a rock group has to use powerful amplifiers if they play in a large auditorium (so the listeners far away can be "blasted" with loud music as well!), and why you cannot use cheap walkie-talkies to talk to someone far away, but must use a cellular phone instead (cellular phones have base stations in each area covered by service, because the power received drops according to the inverse square law).