An object is placed at a distance of 41.4 cm from a thin lens along the axis.If a real image forms at a distance of 36.1 cm from the lens,on the opposite side from the object,what is the focal length of the lens?
A)19.3 cm
B)38.8 cm
C)10.6 cm
D)282 cm
E)6.21 cm

Question

Quizplus · Accepted Answer

Using the lens formula, $ \frac{1}{f} = \frac{1}{v} - \frac{1}{u} $, where $ f $ is the focal length, $ v $ is the image distance (36.1 cm), and $ u $ is the object distance (-41.4 cm, negative because it's on the opposite side of the light coming in). Plugging in the values, $ \frac{1}{f} = \frac{1}{36.1} - \frac{1}{-41.4} $, solving for $ f $ gives approximately 19.3 cm.

An Object Is Placed at a Distance of 41