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MHT CET 2021 (22 Sep, Shift 1) · Spherical Surfaces & Thin Lenses

Spherical Surfaces & Thin Lenses question from MHT CET 2021 (22 Sep, Shift 1)

Q77MHT CET 2021 · 22 SEP · SHIFT 1Medium

Spherical Surfaces & Thin Lenses

A biconvex lens (R1=R2=30 cm)(R_1 = R_2 = 30\text{ cm}) has focal length equal to the focal length of concave mirror. The radius of curvature of concave mirror is [Refractive index of material of lens =1.6= 1.6 ]

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Answer: (c)

  1. 1f=(1.6−1)(130+130)=0.6×230=125\frac{1}{f} = (1.6 - 1)\left(\frac{1}{30} + \frac{1}{30}\right) = \frac{0.6 \times 2}{30} = \frac{1}{25}
  2. f=25f = 25 cm = focal length of the mirror.
  3. Mirror: R=2f=50R = 2f = 50 cm.
  4. So the answer is (c) 50 cm.
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