# physics

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A screen is placed exactly one meter away from an illuminated test pattern. A lens placed between them forms a clear (focused) image of the pattern on the screen when the center of the lens is 200 mm from the test pattern. What is the focal length of the lens? ( cm)

• physics -

o= 200mm
i=1000-200mm if I understand the description correctly.

1/o+1/i=1/f
1/200+1/800=1/f

f= 200*800/1000= 160mm

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