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JEE Main 2021 (27 Aug, Shift 1) · Reflection & Mirrors

Reflection & Mirrors question from JEE Main 2021 (27 Aug, Shift 1)

Q31JEE Main 2021 · 27 AUG · SHIFT 1Medium

Reflection & Mirrors

An object is placed beyond the centre of curvature C of the given concave mirror. If the distance of the object is d1 from C and the distance of the image formed is d2 from C, the radius of curvature of this mirror is:

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Answer: (a)

  1. Object beyond C: ∣u∣=R+d1|u| = R + d_1; image is between F and C: ∣v∣=R−d2|v| = R - d_2.
  2. 1R+d1+1R−d2=2R\frac{1}{R + d_1} + \frac{1}{R - d_2} = \frac{2}{R}
  3. R(2R+d1−d2)=2(R+d1)(R−d2)⇒R(d1−d2)=2d1d2R(2R + d_1 - d_2) = 2(R + d_1)(R - d_2) \Rightarrow R(d_1 - d_2) = 2d_1d_2
  4. R=2d1d2d1−d2R = \frac{2d_1d_2}{d_1 - d_2}, so the answer is (a).
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