Let's assume that the object distance from the lens is u, the image distance from the lens is v, and the magnification of the lens is M.
Given that the object distance (u) is 20 cm and the magnification (M) is 3, we can write the formula for magnification as:
M = -(v/u)
Rearranging the formula, we have:
v = -M*u
Plugging in the values, we get:
v = -(3)(20)
v = -60 cm
The lens equation for a convex lens is given by:
1/f = 1/v - 1/u
Plugging in the values, we have:
1/f = 1/(-60) - 1/20
Simplifying the equation, we get:
1/f = -3/60 - 1/20
1/f = -1/20 - 1/20
1/f = -2/20
1/f = -1/10
Taking the reciprocal of both sides, we get:
f = -10 cm
Since the focal length cannot be negative, the focal length of the lens is 10 cm.
An object is 20cm from a convex lens and produce an image which is three times bigger than the object. What is the focal length of the lens?
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