Year 11 Physics
Refraction and Total Internal Reflection
Aim: To determine how light refracts when it passes from one medium to another.
Method:
1.
Write the Heading, Aim, and the word Results on a fresh page of your book.
2.
Set up the lightbox to produce a single light ray.
3.
Place your page under the light ray so that you will be able to trace the light as it
passes from the curved side of the transparent semi-circle, through the centre point
of the flat side and out into air again.
Q1
Why is there no refraction at the curved side of the block?
4.
of
In pencil, trace the light rays before and after refraction for an angle of incidence
a) approx. 20 degrees,
b) approx. 30 degrees,
c) approx. 40 degrees.
NOTE there will also be some reflected light. Indicate this with a dotted
line on your diagrams.
Q2
What happens to the angle of refraction as the angle of incidence increases?
Q3
What happens to the amount of reflected light?
5.
ray)
Using a protractor, measure the angles between the light going in (the incident
and the light going from the block (the refracted ray) back into the air. Remember
the angle is measured from the normal, not the block surface.
6.
Tabulate your results.
7.
Arrange the light ray so that the angle of refraction is 90 degrees
(ie. it just skims the edge of the block). Trace the light path and
measure this critical angle of incidence.
Q4
What is the critical angle of incidence for light passing from glass to air?
Maureen Trotter – Monbulk College - Year 11 Physics - Refraction and Total Internal Reflection
8.
Arrange the light ray so that the angle of incidence is greater than the critical
angle. Trace the path of the light now.
Q5
What happens to the light when the angle of incidence is greater than the
critical angle?
Q6
Use Snell’s Law
n1 sin 1 =
to calculate the ‘expected’ critical angle.
ng sin i = na sin c
ie use:
n2 sin 2
where ng = 1.5 and ng = 1.0
Conclusions:
1
When light goes from air into glass or water, it bends ................ the normal,
ie i.....r
2.
When light goes from glass or water into air, it bends ............... the normal,
ie i
r
3.
if
For light going from air into glass, sin i / sin r = ...........(see previous prac results
you can’t remember this).
4.
When light goes from glass into air, some is.............. (bent) and some is...............
5.
As the angle of incidence is increased, more light is ......................... and the angle
of refraction ...................
6.
If the angle of incidence is large enough, all the light is ...................... back and
none is ..................... This is called TOTAL INTERNAL REFLECTION.
The angle of incidence when this occurs is called the ...................... angle and
is ..... degrees for light passing from glass to air.
Extension Questions:
Q7
With the aid of a diagram, explain how total internal reflection can cause us
to ‘see’ mirages eg on roads, desert and over ice. (text ref. pp. 38-39)
Q8
How must an optical fibre be designed so that light can be shone in one end
of the glass and not leave until the opposite end is reached, even if the fibre is
bent round corners. List two uses of optical fibres. (text ref. p. 40)
Maureen Trotter – Monbulk College - Year 11 Physics - Refraction and Total Internal Reflection