Total Internal Reflection Learning Objectives:

1
Total Internal ReflectionLearning Objectives

• All- understand what total internal reflection is
• Most- Understand how to work out critical angle
• Some- Know what endoscopy is

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P1 E Part 2

• Rebounding Light

3
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.
• What is different about this light source?
• 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 Task
  1 Point

4
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.

5
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.

6
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.
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Refraction

• Light normally travels in
• straight lines, but it can
• bend at the boundary
• between two materials
• with different densities.

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Reflection or Refraction

• Decide which is which from below.
• Reflection, Angle of Incidence, Angle of
  Reflection, Angle of Refraction

A
D
E
B
C
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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.

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Critical Angle

• Can do Task Calculate the critical angle of
  your block of perspex. 3 Points
• Draw your block and draw your normal.
• 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.

11
The Critical Angle
12
Critical Angle

• Have a go at calculating the critical angle for
  your piece of glass.
• 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.

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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
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Total Internal Reflectioninternal, 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.

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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.

16
Submarines 5 Min

• Explain how total internal refraction might be
  used in submarines.

17

• 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

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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.