Introduction to Light

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					Introduction to Light

Electro-Magnetic Radiation
     Today, we will look at…
 What is light?
 From where does light come?

 How does it get here?

 How do materials affect light?

 For what do we use light?

 How do we detect light?




                  Simon Heppenstall,
               Park Lane College, Leeds
               What is light?
 A form of energy
 Electromagnetic Radiation

 Sometimes

    • A particle
    • A wave
   Photon


                      Simon Heppenstall,
                   Park Lane College, Leeds
         A form of energy
 There are many forms of energy.
 Energy can neither be created nor
  destroyed: just changed from one
  form to another.
 Another form of energy associated
  with light is heat.
 Sound is also a form of energy.

 We use energy to do things.

                 Simon Heppenstall,
              Park Lane College, Leeds
     Electromagnetic Radiation
 For us, this comes from the sun.
 Short wave (ie <400nm)

    • Ultraviolet, X-rays, Gamma rays
   Visible (400nm>x>750nm)
    • Colours from Violet to Red
   Long wave (>750nm)
    • Infrared, microwave and radio waves


                     Simon Heppenstall,
                  Park Lane College, Leeds
                 Sometimes
   A Particle
    • Newton believed this
    • No-one dare argue
   A Wave
    • James Clerk Maxwell believed this
       Discovered that electricity and magnetism
        travelled at the speed of light
       The decided that light must be an electro-

        magnetic wave.

                       Simon Heppenstall,
                    Park Lane College, Leeds
              A photon
 A photon behaves like a wave in
  space
 A photon behaves like a particle near

  matter
 Light is not waves, nor is it
  particulate. It is photonic.



                  Simon Heppenstall,
               Park Lane College, Leeds
    From where does light come?
 The Sun
 The Stars

 Artificial light sources




                   Simon Heppenstall,
                Park Lane College, Leeds
                      The Sun
 Source of most of our natural light
 15 million K at centre

 Diameter of 864,000 miles

 99% total mass of solar system

 Runs in 11 year cycles

 “Day” of between 25 and 27 days

 Further Information:
    • N.A.S.A. Site
                         Simon Heppenstall,
                      Park Lane College, Leeds
              The Stars
 A minor source of light for us
  because of their distance away
 Help with navigation around the
  globe
 Light takes between 4 years and 15
  billion years to get to Earth from the
  stars
 They could have all gone out 3½
  years ago
                  Simon Heppenstall,
               Park Lane College, Leeds
      Artificial Light Sources
 Second most important source to us
  now
 Light pollution stops us from seeing

  the stars
 Usually a conversion of electrical
  energy to light and heat energy
 Sometimes a conversion of chemical

  energy to light and heat energy
                 Simon Heppenstall,
              Park Lane College, Leeds
    How does light get here?
 Light travels in straight lines
 It travels about 186,000 miles per
  second
 Light speed is not relative, ie the
  light travelling from the front of a
  train is travelling at the same speed
  as light travelling from a tree
 It takes 8 minutes for light to get
  from Earth to the sun
                  Simon Heppenstall,
               Park Lane College, Leeds
    How do materials affect light?
 Refraction
 Reflection

 Diffraction

 Transparent

 Translucent

 Opaque




                   Simon Heppenstall,
                Park Lane College, Leeds
       What is Refraction?
 Materials have a property called the
  refractive index
 If light moves from one material to
  another with a different refractive
  index, it bends
 This bend is called refraction.

 Different frequencies of light bend by
  different amounts. White light is
  split into colours
                  Simon Heppenstall,
               Park Lane College, Leeds
       What is Reflection?
 Some materials are shiny (metals)
 Shiny materials make some light
  bounce back
 This is called reflection

 The light from the moon is reflected
  light



                  Simon Heppenstall,
               Park Lane College, Leeds
       What is Diffraction?
 This is complicated, but when light
  hits an edge or a corner, a tiny
  amount is bent round the corner.
 The only place you are likely to see

  this effect is in the science lab.
 You need a LASER and a mesh called
  a diffraction grating.


                 Simon Heppenstall,
              Park Lane College, Leeds
What is a Transparent Material?
 A transparent material allows light to
  pass through it
 Transparent means see-through

 Glass and water are transparent

  materials
 Even coloured glass is transparent




                  Simon Heppenstall,
               Park Lane College, Leeds
What is a Translucent Material?
 A translucent material allows some
  light to pass through it
 Usually, the view through a

  translucent material is not very clear,
  but you can make out shapes
 Tracing paper is translucent




                  Simon Heppenstall,
               Park Lane College, Leeds
    What is an Opaque Material?
 An opaque material does not allow
  light to travel through it
 If you placed a light source next to

  an opaque material, you would get a
  shadow at the opposite side of the
  object to the light
 Wood is an opaque material




                 Simon Heppenstall,
              Park Lane College, Leeds
    How is a shadow formed?
 A shadow is formed when light is
  blocked
 Umbra – full shadow (darkest bit)

 Penumbra – half shadow (lighter)

 Penumbra is formed when the light
  source is larger than the object or
  there are two light sources

                  Simon Heppenstall,
               Park Lane College, Leeds
    For what do we use light?
 To   see
 To   measure
 To   cut
 To   entertain




                      Simon Heppenstall,
                   Park Lane College, Leeds
                   To see
 Our eyes have adapted to pick up
  nearly half the wavelengths that the
  sun emits
 Light hits the retina in our eyes

    • Rods respond to dim light: no colour
    • Cones respond to coloured light
   We see in shades of red, green and
    blue
                     Simon Heppenstall,
                  Park Lane College, Leeds
            To measure
 LASER stands for Light Amplification
  by Stimulated Emission of Radiation
 Allows for measurement within a

  fraction of a millimetre




                 Simon Heppenstall,
              Park Lane College, Leeds
                   To cut
   Again, Lasers allow us to cut things
    very accurately




                    Simon Heppenstall,
                 Park Lane College, Leeds
             To entertain
 Fireworks started light entertainment
 Light Shows set to music

 Lasers drawing images in smoke at a
  night club
 Entertainers have to remember that
  light itself is invisible. You can only
  see the effect of light bouncing off
  something, eg smoke particles.
                  Simon Heppenstall,
               Park Lane College, Leeds
       How do we detect light?
   Our Eyes
    • Shape and Shade
    • Colour
   Instruments
    • Cameras
    • Sensors
    • Optical Instruments


                     Simon Heppenstall,
                  Park Lane College, Leeds
    Our Eyes – Shape and Shade
 Shape and Shade is detected by the
  rods in our retina
 Only part of the brain visible from

  outside the body
 Seeing: Cornea Lens  Retina
  Rods and Cones  Optic Nerve 
  Brain


                 Simon Heppenstall,
              Park Lane College, Leeds
           Our Eyes – Colour
 Colour is detected by cones
 A lot of light is needed for cones to
  start to work
 Three types of cone detect

    • Red
    • Green
    • Blue light.


                       Simon Heppenstall,
                    Park Lane College, Leeds
     Instruments – Cameras
 Cameras behave in a similar manner
  to the eye
 Lens  Retina (in the eye)

 Lens  Film (in the camera)

 Light can affect the mood of a
  picture
 Photographers often use filters to

  enhance this affect
                 Simon Heppenstall,
              Park Lane College, Leeds
     Instruments – Sensors
 Electronics are getting more complex
 Light Dependant Resistors (LDR) are
  often used as sensor/switch devices
 Made of Cadmium Sulphide

 Resistance alters with light amount




                 Simon Heppenstall,
              Park Lane College, Leeds
       Optical Instruments
 Galileo invented the telescope
 Infrared instruments allow us to see
  in the dark




                 Simon Heppenstall,
              Park Lane College, Leeds
     Links to other sources of
        information on Light
 Treating Cancer
 Solar System Simulator

 Optics

 Kodak Info on Light

 The National Geographic
  Presentation on Sight and Sound


                 Simon Heppenstall,
              Park Lane College, Leeds
         Safety With Light
 Never look directly at the sun
 Never look into a LASER

 Use your common sense




                  Simon Heppenstall,
               Park Lane College, Leeds
               Quiz Instructions
   You will be set a series of questions about
    the subject, Light. You have to choose
    the best answer available.
   Click on the     next to the answer you
    think is correct. If you are correct, you
    will score two points.
   To find your current score, click on
   To get help, click on
   (If you click help, you only score 1 point)
   Click here to start:
                         Simon Heppenstall,
                      Park Lane College, Leeds
What is the main source of light on
             Earth?

   The Sun



   The stars



   Artificial light


   Get Help (Score Max = 1)                      Tell me my score
                         Simon Heppenstall,
                      Park Lane College, Leeds
What are the three primary colours
             of light?

   Red, Yellow, Green



   Red, Green, Blue



   Red, Yellow, Blue


   Get Help (Score Max = 1)                    Tell me my score
                       Simon Heppenstall,
                    Park Lane College, Leeds
For what does LASER stand?

 Light Amplification by Stimulated
 Electromagnetic Radiation


  Light Amplification by Stimulated
  Emission of Radiation

  Light Amplitude and Stimulated
  Electromagnetic Radiation


 Get Help (Score Max = 1)                    Tell me my score
                     Simon Heppenstall,
                  Park Lane College, Leeds
From what is an LDR made?

 Silicon Oxide



 Cadmium Sulphide



 Silicon Hydroxide


 Get Help (Score Max = 1)                    Tell me my score
                     Simon Heppenstall,
                  Park Lane College, Leeds
Where in the eye would you find
            cones?

  The Cornea



  The Lens



  The Retina


 Get Help (Score Max = 1)                    Tell me my score
                     Simon Heppenstall,
                  Park Lane College, Leeds
What were the first light shows?

   Light and Sound Shows



   Laser Shows



   Fireworks


   Get Help (Score Max = 1)                    Tell me my score
                       Simon Heppenstall,
                    Park Lane College, Leeds
Which of these best describes the
energy conversion in a light bulb?

   Chemical  Light



   Electrical  Light



   Electrical  Light & Heat


  Get Help (Score Max = 1)                    Tell me my score
                      Simon Heppenstall,
                   Park Lane College, Leeds
What detects shade and shape in
           our eye?

  The Lens



  The Cones



  The Rods


  Get Help (Score Max = 1)                    Tell me my score
                      Simon Heppenstall,
                   Park Lane College, Leeds
How fast does light travel?

186,000 miles per hour



186,000 miles per minute



186,000 miles per second


Get Help (Score Max = 1)                    Tell me my score
                    Simon Heppenstall,
                 Park Lane College, Leeds
   How does light travel?

Generally, in straight lines



Into the eye



By splitting into single frequencies


Get Help (Score Max = 1)                    Tell me my score
                    Simon Heppenstall,
                 Park Lane College, Leeds
                 Help One
   There are three basic sources of light
    that we receive
    • Artificial light (bulbs etc)
    • Stars (millions of light years away)
    • Sun (or Sol)
   Which of these affects us most?



                      Simon Heppenstall,
                   Park Lane College, Leeds
             Help Two
 Primary colours are there, not
  because of light, but because of our
  eyes.
 Our cones have a peak sensitivity to

  red, green and blue light. (These are
  the colours they detect best)
 Paint uses red, yellow and blue to

  mix to make all other colours
                 Simon Heppenstall,
              Park Lane College, Leeds
                       Help Three
   LASERS were invented by Charles Townes and Arthur Schawlow in
    the 1950’s
   When an electron changes from a high energy state to a low
    energy state, its atom emits a photon.
   Take a crystal and shine a light on it. The electrons get excited
    and jump up a level.
   As they calm down, they move down a level and emit a photon.
   This causes a chain reaction as these photons excite more
    electrons, which in turn jump up a level and then calm down
    again. More photons are given off.
   The light is amplified as more light comes off than was put in.
   That’s the theory. In practice, lasers are blasted with a small
    amount of radiation.



                              Simon Heppenstall,
                           Park Lane College, Leeds
              Help Four
 Light Dependant Resistors are used
  for turning sections of circuitry on or
  off.
 The chemical formula for the

  material from which they are made is
  CdS
 The Cd has a RAM of 112.41 and

  boils at 1038 Kelvin
                  Simon Heppenstall,
               Park Lane College, Leeds
               Help Five
 The part of the eye that actually
  detects the light passed back to it by
  the lens is called the retina.
 This has the light detection cells in it

 The lens focuses the light coming
  into the eye



                   Simon Heppenstall,
                Park Lane College, Leeds
              Help Six
 The Chinese were the first people to
  witness an artificial light show
 LASERS were invented in the 1950’s

  by Charles Townes and Arthur
  Schawlow
 The electric light bulb was invented
  by Thomas Edison


                 Simon Heppenstall,
              Park Lane College, Leeds
             Help Seven
 Light bulbs are usually powered by
  electricity nowadays, although some
  gas lights still exist
 When a form of energy is changed

  into light, heat is usually given off as
  a by-product
 This heat is a source of inefficiency




                   Simon Heppenstall,
                Park Lane College, Leeds
             Help Eight
 Light entering the eye is focused by
  the lens
 It is focused onto the retina at the

  back of the eye
 The retina is made of about 125
  million sensors called rods and cones
 Cones come in three basic types



                  Simon Heppenstall,
               Park Lane College, Leeds
              Help Nine
 The sun is about 93 million miles
  from the earth
 It takes about 8 minutes for the light

  to get here from the sun
 Which speed would light have to be
  travelling in order to make that
  possible?


                  Simon Heppenstall,
               Park Lane College, Leeds
               Help Ten
   Can you see round a corner?




                   Simon Heppenstall,
                Park Lane College, Leeds
                 Well Done
   The light we
    receive from the
    sun makes up over
    90% of the light
    that we use.
   Only one billionth
    of the energy given
    off by the sun
    reaches the earth.

                     Simon Heppenstall,
                  Park Lane College, Leeds
             Well done
 The three primary colours of light are
  red, green and blue.
 This is because the cones in our eyes

  detect these three colours best.
 The eyes in bees detect ultra violet
  light



                  Simon Heppenstall,
               Park Lane College, Leeds
            That is correct!!
   Lasers are created by stimulating the
    atoms in crystals and this causes a
    chain reaction which leads to more
    light coming out than went in.




                    Simon Heppenstall,
                 Park Lane College, Leeds
    Fantastic. You got it right.
 LDR’s are made from Cadmium
  Sulphide.
 Silicon Oxide is sand and is used to

  in making transistors and diodes




                  Simon Heppenstall,
               Park Lane College, Leeds
          That is correct.
 The retina is a carpet of over 125
  million rods and cones.
 The rods detect the shape and shade

  while the cones detect the colour.
 It is because the cones are best at
  detecting red, green and blue that
  these are the primary colours of
  light.
                 Simon Heppenstall,
              Park Lane College, Leeds
            Well done.
 The Chinese invented the fireworks
  several thousand years ago.
 Thomas Edison invented the electric

  light bulb at the end of the last
  century
 LASERS were invented in the 1950’s
  by Charles Townes and Arthur
  Schawlow
                 Simon Heppenstall,
              Park Lane College, Leeds
              Correct!
 Electrical energy goes into the bulb
  when you turn it on at the switch.
 Light comes out because it brightens

  the room.
 Heat comes out because the bulb
  gets hot.



                 Simon Heppenstall,
              Park Lane College, Leeds
            That is right.
 The job of the lens is to focus the
  light towards the retina
 The Cornea protects the eye and

  starts to focus the light towards the
  retina




                  Simon Heppenstall,
               Park Lane College, Leeds
              Well Done
 Light travels 186,000 miles every
  second
 That means that it takes 8 minutes

  for light to get here from the sun
 It takes over four years for light to
  get here from the next nearest star



                  Simon Heppenstall,
               Park Lane College, Leeds
                Correct!!!
   Generally, light travels in straight
    lines, although a diffraction grating
    and laser can be used to
    demonstrate that a minute amount
    of light does go round corners




                    Simon Heppenstall,
                 Park Lane College, Leeds
         Sorry, that’s incorrect
   Although the stars give off as much
    or more light than the sun, because
    of the distance from the stars to the
    earth, the light that reaches us is
    insignificant.




                    Simon Heppenstall,
                 Park Lane College, Leeds
      Sorry, that’s incorrect
 Although we make a lot of use of
  artificial light, the amount we
  actually produce on earth is very
  small compared to the amount of
  light we get from the sun.
 Light pollution is becoming a problem
  in some of the larger towns and
  cities though.

                 Simon Heppenstall,
              Park Lane College, Leeds
        I’m afraid that is wrong
   Red, yellow and green are all
    primary colours for either light or
    pigment, but they are mixed
    together here




                    Simon Heppenstall,
                 Park Lane College, Leeds
     I’m afraid that is wrong
 Red, yellow and blue are the primary
  colours for pigment (such as paint
  and dye)
 Light mixes together in a slightly

  different way, which means that one
  of these colours is different.
 If you mix yellow and blue pigment,

  you would make the missing primary
  colour of light.
                 Simon Heppenstall,
              Park Lane College, Leeds
              Incorrect
 What you have actually said there is
  that laser stands for light
  amplification by stimulated light. (as
  electromagnetic radiation is light)
 This isn’t too far from the truth, but
  the answer is still wrong.



                  Simon Heppenstall,
               Park Lane College, Leeds
               Incorrect
 This is just a set of words that begin
  with the correct letters.
 Look at the help file when you go

  back to the question.




                  Simon Heppenstall,
               Park Lane College, Leeds
          I’m afraid not.
 You just have to remember that an
  LDR is made from Cadmium Sulphide
 Cadmium is now thought to be

  carcinogenic




                Simon Heppenstall,
             Park Lane College, Leeds
          I’m afraid not.
 You just have to remember that an
  LDR is made from Cadmium Sulphide
 Cadmium is now thought to be

  carcinogenic




                Simon Heppenstall,
             Park Lane College, Leeds
        Sorry, that’s wrong
 The cornea is like the eye’s
  windscreen
 It stops foreign bodies from getting

  into the eye.
 It also starts to focus the light
  towards the lens



                  Simon Heppenstall,
               Park Lane College, Leeds
          Sorry, that’s wrong
   The lens has the job of focusing
    incoming light at the back of the eye




                    Simon Heppenstall,
                 Park Lane College, Leeds
         That’s incorrect
 Light and sound shows are a
  comparatively recent phenomena
 They came about when Pop Music

  took off in popularity




                Simon Heppenstall,
             Park Lane College, Leeds
          That’s incorrect
 The laser wasn’t invented until the
  1950’s
 It wasn’t until the 1980’s that the

  lasers began to be used in night
  clubs and other entertainment
  venues



                  Simon Heppenstall,
               Park Lane College, Leeds
        I’m afraid that is wrong
   Although gas lights use the change
    from chemical to light energy, these
    also give off heat




                    Simon Heppenstall,
                 Park Lane College, Leeds
     I’m afraid that is wrong
 The change from electrical energy to
  light energy also has a by-product:
  heat.
 As bulbs are becoming more

  efficient, this may change at some
  stage, but we are not there yet.



                 Simon Heppenstall,
              Park Lane College, Leeds
           I’m afraid not
 The lens collects the light together
  and focuses it on the back of the eye
 The actual detection is done by the

  retina




                  Simon Heppenstall,
               Park Lane College, Leeds
           I’m afraid not
 Even though the retina detects shape
  and shade, the cones are there to
  detect colour
 The cones detect the three primary

  colours best: red, green and blue




                 Simon Heppenstall,
              Park Lane College, Leeds
    That is not the correct answer
 If light travelled at 186,000 miles per
  hour, it would take 20 days for the
  light from the sun to get to the Earth
 It takes about 8 minutes




                  Simon Heppenstall,
               Park Lane College, Leeds
    That is not the correct answer
 If light travelled at 186,000 miles per
  hour, it would take 8 hours for the
  light from the sun to get to the Earth
 It takes about 8 minutes




                  Simon Heppenstall,
               Park Lane College, Leeds
              Incorrect
 Light does travel into the eye, but
  the question related to how it
  travelled into the eye and
  everywhere else
 Look at the help and then have
  another go



                  Simon Heppenstall,
               Park Lane College, Leeds
              Incorrect
 Light splits into single frequencies
  when it moves from travelling
  through one material to travelling
  through another
 This sometimes causes the rainbow
  effect (or indeed a rainbow when
  travelling from air  water)


                  Simon Heppenstall,
               Park Lane College, Leeds
    You have finished the lesson
 Click on the button below to find
  your final score and get further
  instructions.
 Homework: Research and find

  information so you can add Notes to
  each of these slides



                 Simon Heppenstall,
              Park Lane College, Leeds

				
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