When a converging lens is used in a camera (as in the first drawing), the film m
ID: 2258874 • Letter: W
Question
When a converging lens is used in a camera (as in the first drawing), the film must be placed at a distance of 0.170 m from the lens to record an image of an object that is 3.10 m from the lens. The same lens is then used in a projector (as in the second drawing), with the screen 0.590 m from the lens. How far from the projector lens should the film be placed?
When a converging lens is used in a camera (as in the first drawing), the film must be placed at a distance of 0.170 m from the lens to record an image of an object that is 3.10 m from the lens. The same lens is then used in a projector (as in the second drawing), with the screen 0.590 m from the lens. How far from the projector lens should the film be placed?Explanation / Answer
the first set of data allow you to find the focal length
use the first equation you quote, with image distance=0.170m and
object distance = 3.10m
this gives you the focal length:
1/3.10+1/0.17= 1/f
= f=0.1611 m
now, use this value of f (since you are using the same lens) to find the object distance knowing the image distance is now 0.590m
1/o + 1/0.590=1/0.1611
1/o=1/0.1611-1/0.590
= o=0.221m
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