An object is placed 30 cm from a concave mirror of focal length 20 cm. The image distance is
A{'text': '+60 cm', 'label': 'A'}
B{'text': '+12 cm', 'label': 'B'}
C{'text': '−12 cm', 'label': 'C'}
D{'text': '−60 cm', 'label': 'D'}
Answer & Solution
Correct answer: D. {'text': '−60 cm', 'label': 'D'}
1. With NCERT signs: u = −30 cm, f = −20 cm.
2. 1/v + 1/u = 1/f ⇒ 1/v = 1/f − 1/u = −1/20 + 1/30 = (−3 + 2)/60 = −1/60.
3. v = −60 cm — image is real (negative v in this convention) and 60 cm in front of the mirror.
_Source: NCERT Class 12 Physics Part II, Ch 9 §9.2.3 worked example pattern_
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