JEE Mains · Physics · STD 12 - Ray optics and optical instruments
- JEE Mains 2024
- Hard
- Numerical
In an experiment to measure the focal length ( \(f\) ) of a convex lens, the magnitude of object distance \((x)\) and the image distance \((y)\) are measured with reference to the focal point of the lens. The \(y-x\) plot is shown in figure. The focal length of the lens is _______ \(\mathrm{cm}\).

Pick an option to check your answer.
Answer & Solution
Correct Answer
(D) \(20\)
Step-by-step Solution
Detailed explanation
\(\frac{1}{f+20}-\frac{1}{-(f+20)}=\frac{1}{f}\)
\(\frac{2}{f+20}=\frac{1}{f} \quad f=20 \mathrm{~cm}\)
Or \(x_1 x_2=f^2\) gives \(f=20 \mathrm{~cm}\)
\(\frac{2}{f+20}=\frac{1}{f} \quad f=20 \mathrm{~cm}\)
Or \(x_1 x_2=f^2\) gives \(f=20 \mathrm{~cm}\)
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