- Hello, this is a video
about the Inverse Square Law,
which is a mathematical property we often
see in physics, but in other science too,
that governs a number of things.
Particularly how the
intensity of light changes
over distance, or other things similar,
like the intensity of sound,
would have the same rule.
So I'm demonstrating this with light,
and this is the way I always like
to kind of go through this.
Imagine you've got a square torch.
Your square torch is producing
a certain amount of light
with a certain amount of power,
or intensity, if you like.
If you put a screen in front
of it a certain distance,
you'd get a square of light
projected on that screen.
Okay?
Now, imagine now you double
the distance of that screen.
The size of the light
projection is going to increase
isn't it?
So actually if you double the distance,
the projected shape of light is going to
be twice as wide and twice as tall.
So the area's going to be two squared.
Four times the area.
Now if you think about the
light that's being spread over
that area, it was quite intense
here in that small area.
If you've doubled the
distance, you've quadrupled
the area, and the intensity is
now a quarter of what it is.
So this is called the Inverse Square Law.
If you times the distance by two,
the intensity is one
over the square of that.
Two squared is four, one quarter.
Now, let's just see
that applied elsewhere.
If you went three times the distance,
it would be one-ninth.
If you went to four times the distance,
as you can see on the illustration here,
you've got sixteen times the area,
one-sixteenth the intensity.
So that's the Inverse Square Law,
hope that was helpful.
Thanks for watching.
