1. 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
11/29/2018

2. Refraction
In order to answer these questions we must first learn something about refraction.
Refraction is the bending of light as it passes from one transparent material to another, e.g. from air to glass.
Incident Ray Normal
When light travels from a rarer medium (air) into a denser medium (glass) it bends towards the normal
Air
When light travels from a denser medium (glass) into rarer medium (air) it bends away from the normal
Refracted Ray
Glass
PhysicsSFC
11/29/2018

3. 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
11/29/2018

4. 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
11/29/2018

5. Refraction
When light passes from the sun into our atmosphere it bends by a small amount.
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.
The eye traces the light rays back in a straight line. This is where the sun appears to be.
PhysicsSFC
11/29/2018

6. 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
11/29/2018

7. Refraction
Dispersion occurs in a prism due to refraction. This happens as the different colours in white light refract by different amounts.
Blue/violet refract the most whereas red/orange refract the least.
Red
Orange
Yellow
Green
Blue
Indigo
Violet
White light
Prism
PhysicsSFC
11/29/2018

8. 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
11/29/2018