A thin lens of focal length −12.5 cm has a 5.0 cm tall object placed 10 cm in front of it. What are the size and orientation of the image?
A) 4.0 cm, inverted
B) 4.0 cm, upright
C) 2.8 cm, inverted
D) 2.8 cm, upright
E) 100 cm, inverted

Question

Quizplus · Accepted Answer

The lens formula is 1/f = 1/v - 1/u. Substituting f = -12.5 cm and u = -10 cm, we find v = -5.56 cm. The magnification is -v/u = 0.556, so the image size is 0.556 * 5.0 cm = 2.8 cm. Since the magnification is positive, the image is upright.

A Thin Lens of Focal Length −12