Question

(Figure 1) shows a meter stick held lengthwise along the optical axis of a concave mirror with the focal length f = 40 cm . Part A: How long is the image of the meter stick? Assume that L = 75 cm .

Answer 1

by lens equation

1 / f = 1 / u + 1 / v

1 / 40 = 1 / 75 + 1 / v

v = 85.714 cm

1 / f = 1 / u + 1 / v1

1 / 40 = 1 / (75 + 100) + 1 / v1

v1 = 51.852 cm

length of the image = 85.714 - 51.852

length of image = 33.862 cm