A rod of length 10 cm lies along the principal axis of a concave mirror of focal length 10 cm in such a way that its end closer to the pole is 20 cm away from the mirror. The length of its image is:
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Question

A rod of length 10 cm lies along the principal axis of a concave mirror of focal length 10 cm in such a way that its end closer to the pole is 20 cm away from the mirror. The length of its image is:

G1 Physics · Accepted Answer

Step 1: Near end at u₁ = −20 cm and far end at u₂ = −30 cm; f = −10 cm. Step 2: 1/v₁ = 1/f − 1/u₁ = −1/10 + 1/20 = −1/20, so v₁ = −20 cm. Step 3: 1/v₂ = −1/10 + 1/30 = −1/15, so v₂ = −15 cm. Step 4: Longitudinal image length = |v₁ − v₂| = 5 cm. Final answer: (D) 5 cm.