Question

What is the focal length of a lens if an object placed 3.28 cm from the lens produces an image that is 4.11 cm in front of the lens?

Answer 1

Answer:

1.82 cm

Explanation:

The relationship between the object distance (p), image distance (q) and focal length (f) is given by $\frac{1}{p}+\frac{1}{q}=\frac{1}{f}$

According to question,

Object distance (p) = 3.28 cm

Image distance (q) = 4.11 cm

Therefore,

$\frac{1}{3.28}+\frac{1}{4.11}=\frac{1}{f}\\\frac{3.28+4.11}{3.28\times 4.11}=\frac{1}{f}\\f=\frac{3.28\times 4.11}{3.28+4.11}\\=\frac{13.48}{7.39}\\=1.82\,\,cm$