An object 4 cm tall is placed 30 cm in front of a concave mirror of focal length 20 cm. Image position and size:
Av = 30 cm
Bv = 12 cm
Cv = 60 cm, h = 8 cm, inverted, real
Dv = -60 cm
Answer & Solution
Correct answer: C. v = 60 cm, h = 8 cm, inverted, real
1/v + 1/u = 1/f. Using u = -30 cm, f = -20 cm (concave): 1/v = 1/(-20) - 1/(-30) = -1/60 → v = -60 cm (in front of mirror, real). m = -v/u = -(-60)/(-30) = -2. Image height = -2 × 4 = -8 cm (inverted, 8 cm tall).
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