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8.3Physics 02. Light And Sound

Describe reflection at a plane surface and use the law of reflection — Cambridge Checkpoint Science 0893 Revision Notes & Topical Questions

5 min read 8 parts Lesson 3 of 5 1 quiz

📚 Cambridge Checkpoint Science 0893 Hub / Topical Revision
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Lesson summary

8.3 Reflection of light at a plane surface and the law of reflection — CHECKPOINT - Lower Secondary Science 0893 notes: Describe reflection at a plane surface and use the law of reflection to draw ray diagrams.Light travels in straight lines — these lines are called rays.Drawing …

  • Drawing rays
  • Plane mirror
  • Everyday uses
  • Measured from the normal
  • Meaning of a law
  • Incident ray

Part 1 of 6Light rays

1Light travels in straight lines
  • Light travels in straight lines these lines are called rays.
2Drawing rays
  • Drawing rays a ray is drawn with a ruler and has an arrowhead to show the direction.

Part 2 of 6Reflection

Plane mirror
  • Plane mirror a flat mirror, where 'plane' means flat.
Reflection
  • Reflection light bouncing off a surface.
  • A reflection from a curved surface such as a spoon is distorted.
Everyday uses
  • Everyday uses a driver uses a mirror to see a cyclist behind the car.

Part 3 of 6Terms of a ray diagram

TermMeaning
Incident rayThe ray coming onto the mirror
Reflected rayThe ray leaving the mirror
NormalA dashed line at right angles to the mirror where the ray meets it
Angle of incidenceAngle between the incident ray and the normal
Angle of reflectionAngle between the reflected ray and the normal
  • Measured from the normal
    • both angles are measured from the normal, not from the mirror surface.

Part 4 of 6Law of reflection

Law
  • Law the angle of reflection is equal to the angle of incidence.
Meaning of a law
  • Meaning of a law in physics a law is something that always applies.

Part 5 of 6Drawing a reflection ray diagram

1
Draw the mirror and the incident ray reaching the mirror with a ruler.
2
Draw the normal at the point where the ray meets the mirror, using a protractor or set square.
3
Measure the angle of incidence between the incident ray and the normal.
4
Measure the same angle on the other side of the normal.
5
Draw the reflected ray at this angle and add an arrowhead.

Part 6 of 6Investigating the law of reflection

1
Stand a plane mirror upright and draw a line along its front.
2
Draw a normal at the mirror surface.
3
Direct a ray of light from a ray box onto the mirror.
4
Mark points on the incident and reflected rays.
5
Remove the mirror and draw both rays with a ruler.
6
Measure the angle of incidence and the angle of reflection.
7
Repeat for at least four more angles and record the results in a table.
  • Result
    • the two angles are equal, and a graph of one against the other is a straight line.

Key terms

TermMeaning
ReflectionBouncing of light off a surface.
Incident rayThe ray of light that arrives at a surface.
NormalA line at right angles to a surface.
Plane mirrorA flat mirror.
Law of reflectionThe angle of reflection equals the angle of incidence.
Ray diagramA diagram that shows rays of light.

Avoid these mistakes

1
Angles are measured from the mirror — they are measured from the normal.
2
The angle of reflection is bigger than the angle of incidence — the two are equal.
3
The normal is a ray of light — it is a construction line drawn as a dashed line.
4
Only mirrors reflect light — most surfaces reflect some light.

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