comb shadows
Comb shadows
In this simple activity, pupils are required to observe the shadow formed by
a comb when a torch is shone on it. They will find out what happens to the
shadow when the distance between the torch and comb changes.
curriculum links: until 2014
curriculum links: from 2014
Physical processes – Light and sound (Key Stage 2)
light cannot pass through some materials, and this leads to the
formation of shadows.
Light (Upper Key Stage 2)
use the idea that light travels in straight lines to explain why shadows
have the same shape as the objects that cast them, and to predict
the size of shadows when the position of the light source changes.
You could also try...
Pupils could investigate the shadows created by combs with different sized
teeth and different sized gaps between the teeth.
© 4science 2013
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comb shadows
title
Comb shadows
What happens to the shadow of a comb when the light source is moved closer or further away?
equipment
• torch
• comb
• piece of white paper
• sunny day
• ruler
• sticky tape
method
1. Stick the paper to a wall at approximately chest height.
2.Hold the comb with its teeth pointing down in front of the paper, about 20 cm away from it.
3.Now hold the torch about 10 cm away from the comb and shine to form a shadow of the comb on
the paper.
4.Sketch a diagram to show what the shadow of the comb looks like.
5.Move the torch away from the comb and then back again. Observe and describe any changes to
the comb’s shadow.
6.Repeat this investigation outside or by a window so that the light source is the Sun rather than
the torch. Observe and describe the shadow formed.
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comb shadows
results
Sketch diagrams and record observations below.
Torch 10 cm from comb
paper
comb
light
shadows
Moving the torch away from and towards the comb
The nearer the torch is to the comb, the more the shadow fans out. The shadow is also darker and
clearer. The further away the torch from the comb, the less the shadow fans out but it becomes
fainter and less clear.
Light from the Sun
Shadows of the comb’s teeth do not spread out. They are almost parallel.
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comb shadows
thinking about what you did
Light travels in straight lines. These are often called rays.
They come out in all directions from a light source such as a light bulb.
A torch is designed to focus the light from a light bulb into a beam.
ligtbulb
torch
beam of light
a reflective surface on the inside
a. Explain why the shadow of the comb is formed.
b. Draw diagrams showing the path of the light rays when i) the torch is close to the comb, and ii)
when the torch is further away from the comb.
c. Explain why the shadows of the comb’s teeth are almost parallel when formed by light from the Sun.
------------------------------------------------------------------------------a. Light can pass through the gaps between its teeth. However, the comb’s teeth block the light, not
allowing it to pass through. So, some light reaches the paper but where it cannot, a shadow forms.
b.
paper
i)
light
shadows
comb
i)
c. Because the Sun (the source of light) is so far away (about 93,000,000 miles).
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