# Total Internal Reflection Learning Objectives by mikeholy

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```									Total Internal Reflection
Learning Objectives:

All- understand what total internal
reflection is
Most- Understand how to work out
critical angle
Some- Know what endoscopy is
P1 E – Part 2
• Rebounding Light
Optical Fibre
• I have in front of me a light source.
• Does any one know the name of the light
source?
• This is known as a fibre optic or an optical fibre.
• In an optical fibre the end of the light is bright
because the light is bouncing around inside the
fibre until it gets to the end.
• Draw an optical fibre and show me how you
think the ray of light travel along it. – Can Do
How does light travel?
• Light Travels in a straight line.
• Reflection is found when light rebound of a mirror.
• Refraction happens when light travels from one material
to another. The ray of light is no longer straight.
• Activity 1.
• Set up your ray box.
• Draw a line on the piece of paper, showing light
travelling in a straight line.
• Put a mirror in front of the light beam and draw the light
being reflected
• Put a piece of glass in front of it and show the light being
refracted.
• Label your lines, Reflection and Refraction.
Labelling up
• Label your diagram, with the normal,
perpendicular to the mirror, measure your
angle of incidence and your angle of
reflection using the protractor.
Labelling Up.
Draw the Normal again, measure your angle of
incidence, measure the angle of refraction.
Was your angle of incidence larger or smaller than
the angle of refraction.
Refraction
• Light normally travels in
straight lines, but it can
bend at the boundary
between two materials
with different densities.
Reflection or Refraction
• Decide which is which from below.
• Reflection, Angle of Incidence, Angle of
Reflection, Angle of Refraction
A

D

E

B     C
Critical Angle
• Waves going from a dense medium (e.g.
Perspex) to a less dense medium (e.g. air)
speed up at the boundary.
• This causes light rays to bend when they
pass from glass to air at an angle other
than 90°.
• Beyond a certain angle, called the critical
angle, all the waves reflect back into the
glass. We say that they are totally
internally reflected.
Critical Angle
• Can do Task – Calculate the critical angle of your block
of perspex. – 3 Points
• Draw a line 30 degrees from the normal.
• Draw a line 60 degrees from the normal.
• Put your light source on the thirty line and move it to the
sixty slowly.
• Stop when the light ray is refracted by 90 degres.
• Record the angle on your piece of paper. You will only
be awarded the three point task if you have got the
correct angle.
The Critical Angle
Critical Angle
• Have a go at calculating the critical angle
• This is the angle of incidence when the
angle of refraction becomes 90 degrees.
• Once you have done this use the prisms to
try and complete the sheet to figure how a
periscope works.
The angle of incidence at which maximum refraction occurs
is called the critical angle, c.

For water this is about 49°. For angles greater than this total
internal reflection results:
Total Internal Reflection
internal, optical, little, bent, light,
An -------- fibre is a thin rod of high-quality
glass. Very ------ light is absorbed by the
glass. ------ getting in at one end undergoes
repeated total ---------- reflection, even when
the fibre is -----, and emerges at the other
end.
Up Periscope
• If you have two right angled prisms, you
can make a periscope which reflects the
light at right angles around a corner.
• In your groups, have a go at making a
persicope with your two perspex blocks.
• Show me how it works.
Submarines – 5 Min
• Explain how total internal refraction might
be used in submarines.
• They are used in telecommunications to
transmit telephone conversations and data

• Whilst traditional copper wires can be
used (and indeed are for the first 500 m or
so from your phone) they cannot carry as
much information and suffer from
magnetic interference
Endoscopy
• Optical fibres are used in endoscopes that
allow surgeons to see inside their patients.
• The endoscope is a long flexible tube that
can be swallowed.
• It has a camera and light inside it.

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