Direct and Indirect Light

Direct Light Produces More Heat

For this we will do another very simple experiment. You
need a flashlight and a piece of paper.

First of all you need to experiment a little with the
flashlight. Put your hand up against the light source. Feel that it is warm.
Move your hand away just a little. Notice how the heat is less, but it is still
warm. Move your hand further and nearer the light, tip it so it is at an angle.
Can you feel any differences?

Now you can show the way light produces heat using your
paper. You will also need a watch and a ruler or tape measure and a large book

First you need to make sure your paper is cold. Pop it in
the freezer for a few minutes; try to keep it dry.

Prop the book up at and angle and lay the piece of paper
on it. Lay the flashlight on another book so that it shines onto the paper. Feel
the paper and notice when it starts to get warm. Measure three inches from the
light source and mark the spot on the paper. Keep feeling that bit. How long
does it take to get warm?

Mark your findings down.

Now repeat the whole thing. Cool your paper again. This
time prop your book upright three inches away from the light. Fix your paper to
it with a piece of tape. Check the area of the paper opposite the center of the
flashlight. How long does it take the paper to get warm this time? Check the
area to the top of the paper. Which is warmer, the top or the center?

The reason that it was quicker the second time is that
the light was falling directly onto the paper. The first time round it was
striking the paper at an angle. Direct light produces more heat than indirect
light, or light striking something at an angle. This is also why the top of the
paper the second time around was not as warm as the center.


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