Question

a lease forms a image of an object. The object is 16.5 cm from the lens. The image is 16.7 cm from the lens on the same side as the object. what is the focal length of the lens?

Answer 1

we know from the lens equation

$\frac{1}{f} = \frac{1}{d_0}+ \frac{1}{d_i}$

where,

d₀ = object distance = 16.5 cm

d_i = image distance = -16.7 cm (negative, since its on the same

thus, we get

$\frac{1}{f} = \frac{1}{16.5}- \frac{1}{16.7}\\ \\ \Rightarrow f = \frac{(16.5)(16.7)}{16.7-16.5} = 1377.75~cm$