3 · IGCSE Physics
Refraction through a glass block
Change the angle of incidence and refractive index (or drag on the diagram) to see how a ray bends through a rectangular block and how far it is shifted sideways. Switch to the semicircular block to find the critical angle and total internal reflection.
Drag above the block (or below the centre in semicircle mode) to set the angle of incidence.
n = sin i ÷ sin r
n₁ sin θ₁ = n₂ sin θ₂
d = t sin(i − r) ÷ cos r
Try this
- With n = 1.50 and i = 40°, read off r and check that sin i ÷ sin r equals n. Repeat at i = 20° and 60°.
- Keep i = 50° and double the thickness from 3 cm to 6 cm: does the lateral displacement d double? What is d at i = 0°?
- In semicircle mode, raise i slowly until the refracted ray skims along the flat face. Compare that angle with c = sin⁻¹(1 ÷ n), then try n = 2.00.
Common error: measuring angles of incidence and refraction from the surface of the block instead of from the normal, which gives the complement of the correct angle.