Refraction & Lens
A beam of light in air strikes a slab of glass (n=1.52) and is partially reflected. Find the
angle of incidence if the angle of reflection is twice the angle of refraction.
An 80-mm-focal-local-length lens is used to focus an image on the film of a camere. The
maximum distance allowed between the lens and the film plane is 120mm. What is the
closest object this length could photoraph sharply?
- Prof. PhysicsLv 71 decade agoFavorite Answer
1. In fact, the angle of reflection equals the angle of incidence.
By Snell's law,
n1sin@1 = n2sin@2
(1.0003)sin@1 = 1.52sin(@1/2)
2sin(@1/2)cos(@1/2) = (1.52/1.0003)sin(@1/2)
cos(@1/2) = 0.75977
Angle of incidence, @1 = 81.1*
2. Focal length, f = 80 mm
Image distance, v = 120 mm
By lens formula,
1/f = 1/u + 1/v
1/80 = 1/u + 1/120
Object distance, u = 240 mmSource(s): Physics king