JEE Advanced 2023 · Paper 1 · Physics Q10

← JEE Advanced 2023 · Paper 1

PhysicsInteger+4Question 27 of 51

In an experiment for determination of the focal length of a thin convex lens, the distance of the object from the lens is $10 \pm 0.1$ cm and the distance of its real image from the lens is $20 \pm 0.2$ cm. The error in the determination of focal length of the lens is $n$ %. The value of $n$ is _____.

Your answer

Answer and worked solution

Official answer: 1

Focal length. For a real image (magnitudes), $\dfrac1f=\dfrac1u+\dfrac1v$ :
$f=\frac{10\times20}{30}=\frac{20}{3}\ \text{cm}.$

Error. Differentiating:
$\frac{\Delta f}{f^2}=\frac{\Delta u}{u^2}+\frac{\Delta v}{v^2}=\frac{0.1}{100}+\frac{0.2}{400}=0.0015.$

$\frac{\Delta f}{f}=0.0015\times\frac{20}{3}=0.01=1\%.$

Topics:Errors in measurement Thin lenses and lens maker's formula Focal length measurements

← Previous question Next question →

JEE Advanced 2023 · Paper 1, Physics question 10