Question

B Review You are standing 0.50 m in front of a lens that projects an image of you onto a wall 1.7 m on the other side of the lens. Part A What is the focal length of the lens? Express your answer in meters. IVO AO ? f = 0.26 m

My answer is wrong. Please help.

Answer 1

Given the object distance u is 0.50m in front of the lens and the image distance v is 1.7m on the other side of the lens. By sign convention u = -0.50m and v = +1.7m. If f is the focal length of the lens, by lens formula

$\frac{1}{f}=\frac{1}{v}-\frac{1}{u}=\frac{u-v}{uv}$

$f=\frac{uv}{u-v}=\frac{-0.50\times 1.7}{-0.50-1.7}=0.39m$

So the focal length of the lens is 0.39m.