Question

An object 3 cm tall is placed 20 cm from the front of a concave mirror with a radius of curvature of 30 cm. A. Compute the focal distance of the focal point to the mirror. B. Compute the image distance from the lens C. Look at the magnification distance in problem 2, and compute the magnification of the image.

Answer 1

a. 15 cm

b. 60 cm

c. -3

Step-by-step explanation:

Given:

object distance, u = 20 cm

radius of curvature, R = 30 cm

a) the focal distance of the focal point to the mirror is given by half of the radius of curvature = R / 2 = 30/2 = 15 cm

b) from the lens equation, we have

1/f = 1/u + 1/v where

f = focal length = 15 cm

u = object distance = 20 cm and v = image distance

hence 1/15 = 1/20 + 1/v

Hence, v = 60 cm

c) magnification M = -v/u

hence m = -60/20 = -3