Light
•Refraction of light including identification of the normal, angle
of incidence and angle of refraction.
•Description of refraction in terms of change of wave speed.
Refraction
:
Waves change speed when they travel from on medium to
another.
This means they sometimes change direction.
An analogy to explain refraction.
Soldiers marching on concrete and sand,
concrete
When they reach the
sand the soldiers
slow up.
The soldiers at the
left of each row reach
the sand first so slow
before the ones at
the right.
The column changes
direction.
sand
air
Normal – at right angles t
the boundary
i
i – incident angle
r – refracted angle
water
r
Shine a single ray of light through a rectangular block. Draw
where it goes on a diagram in your jotter.
You should draw an arrow
each time the line changes
direction.
Now use 3 rays of light to shine on the two lenses. The middle ray
should go straight through.
Convex lens
Concave lens
When the angle in the air gets to 90o it can no longer be
refracted and is then reflected. This is called total internal
reflection.
Total internal reflection
refraction
Smaller than
critical angle
demo
Critical angle –
when refracted
angle is 90o
Larger than
critical angle
Use of total internal reflection - Optical fibre demo
Endoscopes – to look inside people
Uses of refraction - Glasses
No correction needed
Demo of
eyesight
correction
Normal eye
Myopia (nearsightedness)
Hyperopia (farsightedness)
Corrected with concave lens
Corrected with convex lens
No one’s perfect