A-Factor

Optics

Refraction & lenses

Light crossing a boundaryn₁ sinθ₁ = n₂ sinθ₂

Parameters

Angle of incidence θ₁35 °
n₁ (top medium)1
n₂ (bottom medium)1.5

Calculated

Angle of refraction θ₂22.5 °
Critical angle θc—
n₂/n₁ ratio1.500
Bendstowards normal

Curriculum

WAECNECOIGCSESATJUPEB

📋 Teacher notes

  • •Into a DENSER medium (n₂ > n₁): light bends TOWARDS the normal. Into a less dense medium: away from it.
  • •The critical angle only exists going dense → less dense; sinθc = n₂/n₁.
  • •Beyond θc, ALL light reflects: total internal reflection — the basis of optical fibres and diamond sparkle.
  • •Refractive index n = c/v = sinθ₁/sinθ₂ = real depth / apparent depth (three exam definitions of the same thing).
  • •Diamond → air: θc ≈ 24.4° — tiny, which is why diamonds trap and bounce light so much.

✏️ Exercises