A rod of length 10 cm lies along the principal axis of a concave mirror of focal length 10 cm, as shown in the figure. The nearer end of the rod is 20 cm from the pole of the mirror, so the farther end is 30 cm from the pole. What is the length of the image of the rod?

Question

G1 Physics · Accepted Answer

For the nearer end A: u(A) = -20 cm, f = -10 cm. Using 1 ÷ f = 1 ÷ v + 1 ÷ u, we get v(A) = -20 cm. For the farther end B: u(B) = -30 cm. Thus, 1 ÷ (-10) = 1 ÷ v(B) + 1 ÷ (-30). Therefore, v(B) = -15 cm. The image extends from 15 cm to 20 cm from the pole, so its length is 20-15 = 5 cm. Correct option: B.