Science

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  • Created by: soph_g3
  • Created on: 18-10-20 18:54

Light waves

  • Light is a wave thats transfers energy 
  • Light is produced by luminous objects such as ;
    • Sun
    • Candles
    • Lights bulbs
    • Flames
    • Glow worms
  • Light is a wave that always travel in a straight line
  • Like waves in water, light waves are transverse
    • They have undulations at right angles to the direction the wave is travelling in
  • Like water waves light waves transfer energy
  • Light waves can be reflected
  • Water waves travel and transfer energy via moving particles
  • Light waves however dont need particles to travel
  • Light waves are slowed down by moving particles
  • Light travels faster...
    • In a vaccum 
    • With fewer particles to get in the way
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Vaccums

  • The speed of light in a vaccum is always 3x108  m/s
    • Thats 300,000,000 metres per second
  • This means light from the sun gets to earth is 8.3 minutes - even though its 150,000,000km away
  • Nothing travels faster than light in a vaccum
  • Although light is slower when it has to travel through matter, like air or water, its still so fast that the movement appears instant to the human eye 

Speed of light waves in a vaccum = 3 x 108 m/s

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Reflection

  • Light wave is also known as a light ray
  • Mirrors have smooth shiny surfaces which allows light rays to reflect off it at the same angle giving a clear reflection. This is specular reflection.
  • Rough surfaces look dull becaus ethe light is reflected back in lots of different directions. This is called diffse reflection or diffuse scattering.

Law of reflection

  • The angle of incidence and the angle of reflection are always between the light ray and the normal.
  • The normal is a line at a right angle to the surface

Angle of incidence = Angle of reflection

Angle i = Angle r

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Refraction

  • Refraction happens when light rays move to a more or less dense substance
  • Light will travel through transparent material but not opaque 
  • Any substance that light travels through is calle da medium
  • When light travels from one transparent medium to another it bends or refracts

When light goes from a LESS DENSE medium to a MORE DENSE medium : light bends TOWARDS THE NORMAL

When light goes from a MORE DENSE medium to a LESS DENSE MEDIUM : light bends AWAY FROM THE NORMAL 

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How we see

  • When luminous objects produce light, it reflects off non-luminous objects
  • Some of the relected light then goes into our eyes and thats how we see
  • A lense refracts (bends) light
  • A convex lense bends outwards, it causes rays of light to move together to a focus
  • In the human eye the cornea does most the focusing - the cornea is a transparent window with a convex shape.
  • The convex lense behind the cornea changes shape to focus light from objects at varying distances
  • The iris is the coloured part of the eye, it controls the amount of light entering the eye
  • Images are formed on the retina. Cells int the retina are sensitive to light
  • Energy is carried by light. Anything that absorbs this energy is called an absorber.Energy is transferred to the absorber when it hits it. When light hits the retina it causes chemical and elecetrical changes in special cells that send signals to the brain.
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Colour

  • White light is a mioxture of colours
  • The order the colours coem out in are -
      • Red
      • Orange
      • Yellow
      • Green
      • Blue 
      • Indigo 
      • Violet
  • The frequency of light is the number of complete waves that pass a point per second
  • Light waves increase from read (low frequency) to violet (high frequency)
  • Blue jeans are blue because they reflect blue light and absorb all other colours
  • White objects reflects all colours
  • Black objects absorb all clours
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