The image of a tree on a 35 mm color slide is 1.7 mm high.It is to be projected onto a screen 8.0 m from the slide,and is to appear 559 mm high.(a)What focal length lens (in meters)is needed? (b)What is the distance in meters between the lens and the slide? (c)What is the magnification of the system?
A)(a)0.02 m (b)0.02 m
(c)329
B)(a)0.02 m (b)7.98 m
(c)0.00
C)(a)0.02 m (b)-0.02 m
(c)0.00
D)(a)0.02 m (b)-8.02 m
(c)0.00

Question

Quizplus · Accepted Answer

Using the equation for magnification: 
m = -di/do = hi/ho

where di is the distance between the lens and the slide, do is the distance between the lens and the screen, hi is the height of the image on the screen, and ho is the height of the object on the slide. 
Substituting the given values: 
m = -di/8 = 559/1.7 
Solving for di: 
di = -0.02 m

Using the thin lens equation: 
1/f = 1/do - 1/di 
Substituting the given values and solving for f: 
f = 0.02 m

Therefore, the correct choice is A, where the focal length of the lens is 0.02 m and the distance between the lens and the slide is also 0.02 m. The magnification of the system is 329.

The Image of a Tree on a 35 Mm Color