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7.12Chapter 7: Light

Chapter 7 Review: Light — Alhussan Physics - Stage 8 Revision Notes & Topical Questions

5 min read 8 parts Lesson 12 of 12 1 quiz

📚 Alhussan Physics - Stage 8 Hub / Topical Revision
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Lesson summary

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

1Straight lines
  • Light travels in straight lines at about 300 000 km/s.
2Luminous and non-luminous
  • Luminous objects emit light and non-luminous objects reflect it.
3Materials
  • 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.
4Distances
  • Distances in space are measured in light minutes, light hours and light years.

Part 2 of 6Reflection and images

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

Part 3 of 6Refraction and total internal reflection

Refraction and total internal reflection
Refraction
  • Light 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 block
  • Draw 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 normal
  • A ray along the normal passes through without bending.
Total internal reflection
  • A ray in a denser medium whose angle of incidence is greater than the critical angle is totally reflected.
Uses
  • Optical fibres, endoscopes and prisms use total internal reflection.

Part 4 of 6Dispersion and colour

Dispersion
  • White light splits into a spectrum, with violet refracted most and red least.
Primary colours of light
  • Red, green and blue; the secondary colours are yellow, cyan and magenta.
Filters
  • They absorb some colours and transmit others, so they subtract colours.
Coloured objects
  • They look coloured because they reflect some colours and absorb others.

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

Eye
  • The cornea and lens focus an inverted image on the retina, which contains rods and cones.
Camera
  • A lens focuses an inverted image onto film or a sensor.
Models of light
  • Newton 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.

Key terms

TermMeaning
RefractionThe bending of light when it changes speed at a boundary.
DispersionThe splitting of white light into a spectrum.
Critical angleThe angle of incidence at which the angle of refraction is 90°.
Primary colours of lightRed, green and blue.
TranslucentTransmitting light but not allowing clear images.

Avoid these mistakes

1
Measuring angles from the mirror surface — angles are measured from the normal.
2
Thinking light bends away from the normal entering glass — it bends towards the normal.
3
Thinking a filter adds colour — it removes the other colours.
4
Thinking the image on the retina is upright — it is inverted.

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