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NEET 2012 (AIPMT, Mains) · Reflection & Mirrors

Reflection & Mirrors question from NEET 2012 (AIPMT, Mains)

Q50NEET 2012 · AIPMT · MAINSMedium

Reflection & Mirrors

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 the image is

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Answer: (d)

  1. f=−10 cmf = -10\text{ cm}. Near end at u=−20=2fu = -20 = 2f, i.e. at C, so its image is also at 20 cm.
  2. Far end at u=−30u = -30: 1v=−110+130=−115⇒v=−15 cm\frac{1}{v} = -\frac{1}{10} + \frac{1}{30} = -\frac{1}{15} \Rightarrow v = -15\text{ cm}
  3. Image length =20−15=5 cm= 20 - 15 = 5\text{ cm}
  4. So the answer is (d) 5 cm.
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