Refraction Date
Key words
Reflection
Reflected Ray
Incident Ray
Normal
Refraction
Convex
What do you think is happening in the above photo and why?
https://www.youtube.com/watch?v=o08jgkut7e8
Refraction
Learning Objectives
• Investigate the behaviour of light as it travels from one medium to another.
• Explain the process of refraction using key scientific terms.
• Construct ray diagrams.
© Boardworks Ltd 20041 of 20 © Boardworks Ltd 20053 of 84
1. Place a rectangular
glass block on a
sheet of paper and
draw around it.
2. Draw a normal line
(at 90º) along the top
surface of the block.
3. Shine rays of light with incident [i] angles of 0º, 20º,
40º, 60º, 80º and 90º into the block, making sure they
all hit where the normal line crosses the glass surface.
Measure angle ‘r’ each time and record the results.
angle i
Refraction investigation
angle r
© Boardworks Ltd 20041 of 20 © Boardworks Ltd 20054 of 84
Record the results of the refraction investigation in a table:
Angle of incidence [i]
Angle of refraction [r]
20º
40º
60º
80º
90º
Describe the change of direction of:
the ray as it enters the glass;
the ray as it re-enters the air.
Refraction investigation – results
© Boardworks Ltd 20041 of 20 © Boardworks Ltd 20055 of 84
Refraction in a rectangular block
© Boardworks Ltd 20041 of 20 © Boardworks Ltd 20056 of 84
In the water.
Light moves slower through a more dense medium.
Travelling through different materials
If you were running along a beach and then ran into the
water when would you be moving slower – in the water
or on the sand?
Do you think light moves faster or slower in a more dense
medium?
In a similar way, as light moves from one medium to
another of different density, the speed of light changes.
© Boardworks Ltd 20041 of 20 © Boardworks Ltd 20057 of 84
glass
air
The speed of light waves depends on the material they
are travelling through.
air = fastest diamond = slowestglass = slower
Bending light
If light waves enter a different material (e.g. travel from
glass into air) the speed changes.
This causes the light to bend or refract.
© Boardworks Ltd 20041 of 20 © Boardworks Ltd 20058 of 84
mud
road
Why does light change direction?
Imagine a car driving from the road into a muddy field.
In the muddy field it slows down as there is more friction.
If it enters the field at an angle then the front tyres hit the mud at different times.
Tyre 1 hits the mud first and will move more slowly than tyre 2. This causes the car to turn towards the normal.
When the car leaves the mud for the road, tyre 1 hits the road before tyre 2 and this causes the car to turn away from the normal.
tyre 1 tyre 2
© Boardworks Ltd 20041 of 20 © Boardworks Ltd 20059 of 84
airglass
When light is refracted as it travels from air to glass:
angle of incidence > angle of refraction
i > r
What happens in refraction: air to glass
In general, when light rays
move from a less dense
medium (air) to a more dense
medium (glass) they ‘bend’
towards the normal.
As the light ray travels from
air into glass it moves
towards the normal.
i > r
© Boardworks Ltd 20041 of 20 © Boardworks Ltd 200510 of 84
air
glass
If the two surfaces of the block are parallel, then the ray at the start is parallel to the ray at the end.
When light is refracted as it travels from air to glass:
angle of incidence < angle of refraction
i < r
What happens in refraction: glass to air
In general, when light rays travel
from a more dense medium (glass)
to a less dense medium (air) they
‘bend’ away from the normal.
As the light ray travels from
glass into air it moves away
from the normal.
i < r
© Boardworks Ltd 20041 of 20 © Boardworks Ltd 200511 of 84
Why does light change direction?
If the car approached the muddy field at an angle of
incidence of 0° then both front tyres would hit the mud at
the same time.
The tyres would have the same speed relative to each other
so the direction of the car would not change, it would just
slow down.
© Boardworks Ltd 20041 of 20 © Boardworks Ltd 200512 of 84
Refraction in a rectangular block
© Boardworks Ltd 20041 of 20 © Boardworks Ltd 200513 of 84
If the light enters a new medium along the normal
(i.e. angle of incidence = 0) then it does not ‘bend’
because all of the light ray slows down at the s___ t___.
When light hits a medium at an angle to the n_____
the light ‘bends’ in a similar way to that described for
the car in a muddy field.
Part of the light ray s____ d____ before the rest and
this causes the change of d_______.
ormal
lows
irection
ime
Why does light change direction?
ame
own
© Boardworks Ltd 20041 of 20 © Boardworks Ltd 200514 of 84
Many visual effects are caused by refraction.
Effects of refraction
This ruler appears bent
because the light from one
end of the ruler has been
refracted, but light from the
other end has travelled in a
straight line.
Would the ruler appear more
or less bent if the water was
replaced with glass?
© Boardworks Ltd 20041 of 20 © Boardworks Ltd 200515 of 84
The rays of light from a stone get bent (refracted) as they
leave the water.
Your brain assumes
these rays of light
have travelled in
straight lines.
Your brain forms an image
at the place where it thinks
the rays have come from –
the stone appears to be
higher than it really is.
actual location
image
Apparent depth
© Boardworks Ltd 20041 of 20 © Boardworks Ltd 200516 of 84
The Archer fish is a predator that shoots jets of water at
insects near the surface of the water, e.g. on a leaf.
image
of prey
prey
location
The fish does not aim at
the refracted image it sees
but at a location where it
knows the prey to be.
https://www.youtube.com/
watch?v=_6LsXA_FJIE
The Archer fish
The Archer fish allows
for the refraction of light
at the surface of the
water when aiming at
the prey.
© Boardworks Ltd 20041 of 20 © Boardworks Ltd 200517 of 84
1. When light bends this is called r_ _ _ _ _ _ _ _ _.
Refraction summary
Remember that the angle of reflection [r] and the
angle of refraction [r] use the same symbol.
In reflection: i = r
In refraction: i r
2. Refraction happens because the light changes s_ _ _ _.
3. When light enters a more dense medium (e.g. glass),
it bends t _ _ _ _ _ _ the normal.
4. When light enters a less dense medium [e.g. air],
it bends a_ _ _ _ f_ _ _ the normal.
5. If the incident ray hits a surface at 0º, no refraction occurs
True or false?