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Lesson: Chapter 5 — Optics

5.3. Refraction of light 4 of 5

Through a glass block

Activity 5.4 traces a ray of light into a glass block and out again.

Activity 5.4

  • Lay a sheet of white paper on a drawing board and put a glass block on it. Draw round the block with a sharp pencil (PQRS).
  • Stand a pin A a little away from face PQ and a pin B touching it.
  • Looking through face SR, stand pin C touching SR and pin D a little away from it, so that A, B, C and D all look in line.
  • Remove the pins and block, join AB, BC and CD, and draw the normals at B and C.
A ray AB entering a glass block at B, bending towards the normal along BC inside the glass, and leaving at C along CD, parallel to the direction it came in.
Name
AB Incident ray
BC Refracted ray — bent towards the normal at B
CD Emergent ray — leaving the glass
i Angle of incidence — between the incident ray and the normal
r Angle of refraction — between the refracted ray and the normal
e Angle of emergence — between the emergent ray and the normal at C

The observation

Going from air (rarer) into glass (denser), the ray bends towards the normal. Coming out of the glass into the air it bends away from the normal, and leaves parallel to the way it came in.