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JEE Main 2024 (30 Jan, Shift 2) · Spherical Surfaces & Thin Lenses

Spherical Surfaces & Thin Lenses question from JEE Main 2024 (30 Jan, Shift 2)

Q47JEE Main 2024 · 30 JAN · SHIFT 2Medium

Spherical Surfaces & Thin Lenses

In an experiment to measure the focal length (f)(f) of a convex lens, the magnitude of object distance (x)(x) and the image distance (y)(y) are measured with reference to the focal point of the lens. The y-xy\text{-}x plot is shown in figure.

The focal length of the lens is ________ cm\text{cm}.

Figure

Numerical answer type. Work it out, then open the answer.

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Answer: 20

  1. Distances measured from the foci obey Newton's formula xy=f2xy = f^2.
  2. The curve meets the line x=yx = y (tangent point C) at x=y=20x = y = 20 cm.
  3. f2=20×20⇒f=20f^2 = 20 \times 20 \Rightarrow f = 20 cm
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