Question

A convex lens has its focal length f= 44.8 cm. (a) Where will it focus the object, which is 2.0 m away from the lens? (b) What will be the size of the object's image if the size of the object is 1.5 cm?

Answer 1

Using len's equation for convex lens:

1/v - 1/u = 1/f

1/v = 1/f + 1/u

1/v = 1/44.8 + 1/(-200)

v = 57.73 cm , Hence the object will be focused at a distance of 57.73 cm from the lens.

Magnification = -(v/u) = -(57.73/(-200)) = 0.288

Magnification = Image height/ Object height

0.288 = Image height/1.5

Image height = 1.5 x 0.288 = 0.432 cm