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A lens has a focal length of +20.0 cm, and a magnification of –4.00. What is the distance between the object and the image?

Julius  Jan 15, 2018
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A coupe of physics equations:

 

1/f = 1/do + 1/di      do = object distance   di = image distance

 

and    M = -di/do       or  do = -di/M    (substitute into the first equation)

 

1/20 = 1/(-di/-4) + 1/di

1/20 = 4/di + 1/di

1/20 = 5/di      di = 5(20) = 100 cm

 

M= -di/do

-4 = -100/do     do = 25 cm

Distance between do and di =    100 + 25 = 125 cm

ElectricPavlov  Jan 15, 2018

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