Ray Optics And Optical Instruments Ques 35
35. A boy is trying to start a fire by focusing sunlight on a piece of paper using an equiconvex lens of focal length $10 $ $cm$. The diameter of the Sun is $1.39 \times 10^{9} $ $m$ and its mean distance from the earth is $1.5 \times 10^{11}$ $ m$. What is the diameter of the Sun’s image on the paper?
[2008]
(a) $9.2 \times 10^{-4} $ $m$
(b) $6.5 \times 10^{-4} $ $m$
(c) $6.5 \times 10^{-5} $ $m$
(d) $12.4 \times 10^{-4} $ $m$
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Answer:
Correct Answer: 35.(a)
Solution:
- (a) We have, $|\frac{v}{u}|=\frac{\text{ Size of image }}{\text{ Size of object }}$
or, Size of image $=|\frac{v}{u}|$’ Size of object
$=(\frac{10^{-1}}{1.5 \times 10^{11}}) \times(1.39 \times 10^{9})$ $=0.92 \times 10^{-3} m=9.2 \times 10^{-4} $ $m$
$\therefore$ Diameter of the sun’s image $=9.2 \times 10^{-4} $ $m$.
BETA
