Physics
Physics
Problem
A point object in air is in front of the curved surface of a *plano-convex* lens. The radius of curvature of the curved surface is 30 cm and the refractive index of the lens material is 1.5, then the focal length of the lens (in cm) isIntuitive explanation
A plano-convex lens has one flat surface (which doesn't bend light) and one curved surface doing all the refraction work. The key is using the lensmaker's equation with the understanding that only the curved surface contributes—treat the flat surface as having infinite radius of curvature. This reduces the problem to single-surface refraction, where the curved surface's radius and the refractive index difference between air and glass determine how strongly it focuses light.
Intuitive explanation
A plano-convex lens has one flat surface (which doesn't bend light) and one curved surface doing all the refraction work. The key is using the lensmaker's equation with the understanding that only the curved surface contributes—treat the flat surface as having infinite radius of curvature. This reduces the problem to single-surface refraction, where the curved surface's radius and the refractive index difference between air and glass determine how strongly it focuses light.