P14 Light

• refraction


  the bending of light as it passes from one material to another
• refraction happens because the speed of light changes as it changes from one medium to another
• if light goes from air to glass it bends towards the normal
• if light goes from glass to air it bends away from normal
• if light enters glass at right angles it would carry on as a straight line
• refractive index

  • property of the material
  • how much light slows down by when it enters a material
• refractive index


  sin(i) / sin(r) = real depth / apparent depth = refractive index
• each colour in the visible light spectrum has it's own narrow band of wavelength and frequency
• the colour of light coming from a source depends on the type of source

  • star and lamps- continuous range of wavelength
  • lasers/neon lamps - narrow range of wavelength
• colour filters absorb certain wavelengths and transmit others
• the surface colour an object of an opaque object depends on pigments which absorb or reflect wavelength
• red objects absorb every colour but red which is reflected
• transparent


  light passes through
• translucent 


  light passes through but is scattered
• specular reflection

  • smooth mirror surface
  • reflected at the angle it hits the surface
• diffuse reflection

  • rough surface
  • light is scattered
• colour filters only let that colour light pass through
• objects appear black when all coloured light is absorbed
• all objects emit radiation and the colour of it depends on the object's temperature
• blue is a higher frequency than yellow light so blue objects are often hotter than yellow objects
• convex lens

  • focuses parallel rays to a point called the principle focus
  • converging lens
  • used in magnifying glasses and cameras
• principle focus (focal point)


  the point where light rays meet
• focal length 


  the distance from the centre of the lens to the focal point
• concave lens

  • diverging lens
  • rays refract and diverge in opposite directions so they don't meet
• the position and nature of the image formed by a lens depends on

  • the focal length of the lens
  • the distance from the object to the lens
• in a camera converging lenses are used to produce a real image of an object on a film
• for distant objects, the distance from the lens must be equal to the focal length of the camera
• in magnifying glasses the object must be between the lens and the principle focus
• in magnifying glasses the image is formed on the same side of the lens as the object
• in magnifying glasses the image is virtual, upright and magnified