Physics · Geometrical Optics

JEE Advanced 2018 — Paper 1 — Question 13

Sunlight of intensity $1.3 \mathrm{kWm}^{-2}$ is incident normally on a thin convex lens of focal length 20 cm . Ignore the energy loss of light due to the lens and assume that the lens aperture size is much smaller than its focal length. The average intensity of light, in $k W \mathrm{~m}^{-2}$ , at a distance 22 cm from the lens on the other side is $\qquad$ .

Answer: 130

Numerical answer — enter this value.

Step-by-step solution

The area of A over which the light falls satisfy :

$\frac{A}{A_{\text {lens }}}=\left(\frac{2}{20}\right)^{2}=\frac{1}{100}$

so intensity at $\mathrm{A}=100 \times 1.3=130 \mathrm{~kW} / \mathrm{m}^{2}$ .

Answer key and solution verified before publishing.

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Exam: JEE Advanced 2018
Paper: Paper 1
Subject: Physics
Chapter: Geometrical Optics
Topic: Lenses and Their Combinations, Silvering of Lens