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PHYSICS · Stage 8 · Chapter 7: Light

Physics 7.12 Chapter 7 Review: Light

5 min read 6 parts Lesson 12 of 12

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Physics 7.12 Chapter 7 Review: Light — Alhussan International Academy — Physics (Stages 7–9) notes: Summarise Chapter 7 on how light travels, reflects, refracts, disperses, produces colour and is detected by the eye.Straight lines — Light travels in straight lines at about 300 00…

  • Luminous and non-luminous
  • Law of reflection
  • Plane mirror image
  • Diffuse reflection
  • Refraction
  • Investigating a block

Part 1 of 6Light and seeing

  • Straight lines — Light travels in straight lines at about 300 000 km/s.
  • Luminous and non-luminous — Luminous objects emit light and non-luminous objects reflect it.
  • Materials — Transparent materials transmit light clearly, translucent materials transmit it but scatter it, and opaque materials do not transmit it.
    • White cloth shows light coming through but not a clear image, so it is translucent.
  • Distances — Distances in space are measured in light minutes, light hours and light years.

Part 2 of 6Reflection and images

  • Law of reflectionThe angle of incidence equals the angle of reflection, both measured from the normal.
  • Plane mirror imageIt is virtual, upright, laterally inverted and as far behind the mirror as the object is in front.
  • Diffuse reflectionA rough surface scatters light in many directions, so no image forms.

Part 3 of 6Refraction and total internal reflection

  • RefractionLight bends when it changes speed at a boundary, towards the normal into a denser medium and away from it into a less dense medium.
  • Investigating a blockDraw round a glass block, shine a ray at an angle of incidence, mark the rays going in and out and measure the angles from the normal.
  • Along the normalA ray along the normal passes through without bending.
  • Total internal reflectionA ray in a denser medium whose angle of incidence is greater than the critical angle is totally reflected.
  • UsesOptical fibres, endoscopes and prisms use total internal reflection.

Part 4 of 6Dispersion and colour

  • DispersionWhite light splits into a spectrum, with violet refracted most and red least.
  • Primary colours of lightRed, green and blue; the secondary colours are yellow, cyan and magenta.
  • FiltersThey absorb some colours and transmit others, so they subtract colours.
  • Coloured objectsThey look coloured because they reflect some colours and absorb others.

Part 5 of 6The eye, camera and models of light

  • EyeThe cornea and lens focus an inverted image on the retina, which contains rods and cones.
  • CameraA lens focuses an inverted image onto film or a sensor.
  • Models of lightNewton used a particle model and Huygens a wave model, and modern physics uses both.

Part 6 of 6Journey of light to the eye

  1. Light leaves a luminous source such as a lamp.
  2. It travels in straight lines to an object such as a page.
  3. The page reflects it in many directions.
  4. Some of the light enters the eye.
  5. The cornea and lens focus it on the retina.
  6. The signal passes along the optic nerve to the brain.

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