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Grades 8 and 9 Intermediate About 20 min Version 1 Awaiting review Premium

Refraction: tracing rays through a glass block

Light travels more slowly in glass or water than in air. When a ray crosses into a block at an angle, it changes direction: this is refraction. Going from air into glass, the ray bends towards the normal, so the angle of refraction (r) is smaller than the angle of incidence (i). Leaving the block, it bends away from the normal again, coming out parallel to the original ray but shifted sideways. A ray along the normal does not bend. The refractive index n = sin i ÷ sin r tells you how strongly a material bends light.

What you will learn

  • Trace a ray through a rectangular block and label i and r.
  • Describe how light bends entering and leaving a denser medium.
  • Calculate refractive index using n = sin i ÷ sin r.

Before you start

  • Know the terms ray, normal and angle of incidence.

Materials

  • Rectangular glass block and a clear tank of water
  • White paper, pins, pencil and protractor

Equipment

  • Ray box

Procedure

  1. Shine the ray into the glass block at 20°, 40° and 60°, recording the angle of refraction each time.
  2. Shine the ray along the normal (0°) and record.
  3. Replace the glass with water and repeat at one angle.

How this simulation is simplified

  • Refractive indices: glass 1.50, water 1.33. The block is surrounded by air (n = 1).