Transcript Refraction - TeachNet Ireland

Refraction

Why do swimming pools look less deep
than they actually are?

Is the sun exactly where we see it in the
sky?

Why is the sky blue?

Why are sunsets red/orange?
PhysicsSFC
7/17/2015
Refraction

In order to answer these questions we
must first learn something about
refraction.
Incident Ray
Refracted
Ray
PhysicsSFC
Refraction is the bending of
light as it passes from one
transparent material to another,
e.g. from air to glass.

When light travels from a rarer
medium (air) into a denser
medium (glass) it bends towards
the normal
When light travels from a
denser medium (glass) into
rarer medium (air) it bends
away from the normal
Normal
Air
Glass


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Refraction

This helps to explain why swimming pools
appear less deep than they actually are
The eye traces the light rays back in a
straight line. Where these rays meet is
where the bottom of the pool appears to be
Eye
Apparent Depth
Where the tile
appears to be
Tile at bottom of pool
PhysicsSFC
7/17/2015
Refraction
When light passes from water into air it
refracts quite a bit due to the relatively large
difference in density between water and air.
 The smaller the difference in density between
the two media the less the light refracts
 When light passes from free space (vacuum)
into air it refracts by a small amount.
However, this still has a noticeable effect.

PhysicsSFC
7/17/2015
Refraction

When light passes from the sun into our
atmosphere it bends by a small amount.
Where the sun appears to be
Sun
Sun
Earth's Atmosphere
Earth
The eye traces the light rays back
in a straight line. This is where the
sun appears to be.
PhysicsSFC
For this reason
the sun appears
‘higher’ in the sky
than it actually is.
This ensures that
our days are a
little longer than
they would
otherwise be.
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Refraction





When white light passes through a prism or a
diffraction grating it splits up into the seven colours of
the rainbow.
This phenomenon is called dispersion.
Dispersion occurs in a prism due to refraction.
Dispersion occurs in a diffraction grating due to
diffraction and interference.
To answer the final two questions lets look at
dispersion in a prism.
PhysicsSFC
7/17/2015
Refraction
Dispersion occurs in a prism due to refraction.
This happens as the different colours in white
light refract by different amounts.
Red
Orange
Yellow
Green
Blue
White light
Indigo
Prism
PhysicsSFC
Violet
Blue/violet
refract the
most whereas
red/orange
refract the
least.
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Refraction
We now know:
 why swimming pools look less deep than they
actually are.
 that the sun is not exactly where we see it in
the sky.
But ……………….
 why is the sky blue?

why are sunsets red/orange?
PhysicsSFC
7/17/2015