# Physics

A convex lens forms a real image 6 times the size of the object. The distance between object and image is 33 cm. Find the focal length of the lens.

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1. 1/do + 1/di = 1/f

di/do = 6

di + do = 33

You have to solve three equations in three unknowns. Solve the last two in two unknowns first.

do + 6do = 33
do = 33/7 = 4.714 cm,
di = 28.286 cm

Now solve for f using the first equation.

f = 4.0406 cm

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