Total Internal Reflection Learning Objectives by mikeholy


									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
• 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
         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
• 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.
• 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



           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 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.
The Critical Angle
             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.
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
             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
• 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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