#1 When a converging lens is used in a camera (as in the top figure), the film m

ID: 1787455 • Letter: #

Question

When a converging lens is used in a camera (as in the top figure), the film must be at a distance of 0.210 m from the lens to record an image of an object that is 4.00 m from the lens. The same lens and film are used in a projector (see the bottom figure), with the screen 3.700 m from the lens. How far from the projector lens should the film be placed?
___ m

The distance between an object and its image formed by a diverging lens is 48.5 cm. The focal length of the lens is -232.7 cm.

(a) Find the image distance.
____ cm

(b) Find the object distance.
____ cm

Explanation / Answer

#1. image distance, q = 0.210 m

object distance, p = 4 m

1/f = 1/p +1/q

1/f = 1/0.210 + 1/4

f = 0.20 m

now for projector, q = 3.70 m

1/0.20 = 1/3.70 + 1/p

p = 0.211 m.....Ans

#2. 1/-232.7 = 1/p - 1/q

p - q = 48.5

p = 48.5 + q

p q = - 232.7 (q - p) = -232.7 x -48.5

q = - 133 and 84.7 cm

(A) image distance = - 84.7 cm

(B) object distance = 133 cm