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JEE Main 2026 (4 Apr, Shift 1) · Reflection & Mirrors

Reflection & Mirrors question from JEE Main 2026 (4 Apr, Shift 1)

Q5JEE Main 2026 · 4 APR · SHIFT 1Difficult

Reflection & Mirrors

A rod of length 10 cm lies along the principle axis of a concave mirror of focal length 10 cm as shown in figure. The length of the image is ______ cm.

Figure

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Answer: (b)

  1. f=−10 cmf = -10\text{ cm}, so CC is at 20 cm. The near end at u=−20u = -20 cm images at v=−20v = -20 cm.
  2. Far end at u=−30u = -30 cm: 1v=1f−1u=−110+130=−115⇒v=−15 cm\frac{1}{v} = \frac{1}{f} - \frac{1}{u} = -\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 (b) 5.
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