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JEE Main 2021 (31 Aug, Shift 1) · Spherical Surfaces & Thin Lenses

Spherical Surfaces & Thin Lenses question from JEE Main 2021 (31 Aug, Shift 1)

Q72JEE Main 2021 · 31 AUG · SHIFT 1Easy

Spherical Surfaces & Thin Lenses

An object is placed at the focus of concave lens having focal length f. What is the magnification and distance of the image from the optical centre of the lens?

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Answer: (c)

  1. Concave lens: focal length −f-f, object at u=−fu = -f.
  2. 1v=1−f+1−f=−2f⇒v=−f2\frac{1}{v} = \frac{1}{-f} + \frac{1}{-f} = -\frac{2}{f} \Rightarrow v = -\frac{f}{2}
  3. m=vu=−f/2−f=12m = \frac{v}{u} = \frac{-f/2}{-f} = \frac{1}{2}
  4. So the answer is (c) 12, f2\frac{1}{2},\ \frac{f}{2}.
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