Lesson 5 of 11 · 7 min
Refraction at a spherical surface
NCERT § "Refraction at a Spherical Surface"
Kabir's lens has two curved faces. Before tackling both, look at what just one curved glass surface does to the candle's light.
The lesson in notes
In short
For a single spherical surface separating media of refractive indices n₁ (object side) and n₂, with paraxial rays: n₂/v − n₁/u = (n₂ − n₁)/R.
R is positive when the centre of curvature lies on the side the light goes into (the refracted side), and negative otherwise.
The formula applies to both convex and concave surfaces, with the sign of R taking care of the shape.
Setting R → ∞ gives the flat-surface result, v/u = n₂/n₁, which is the apparent-depth relation.
This result is the building block for the lens maker's formula, obtained by applying it to the two surfaces of a lens in turn.