Refraction & Lens

Question

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?

Update:

呃，抱歉這麼說

但第二題的答案好像應該是大於等於什麼吧？

Update 2:

喔對不起

是我弄錯了＞＜

Answer 1

Favorite 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 mm

Source(s): Physics king