Q138 / 200 · NEET 2008 (Screening) · Physics
A boy is trying to start a fire by focusing sunlight on a piece of paper using an equiconvex lens of focal length $10 \mathrm{~cm}$. The diameter of the sun is $1.39 \times 10^9 \mathrm{~m}$ and its mean distance from the earth is $1.5 \times 10^{11} \mathrm{~m}$. What is the diameter of the sun's image on the paper?
- Correct answerA$9.2 \times 10^{-4} \mathrm{~m}$
- B$6.5 \times 10^{-4} \mathrm{~m}$
- C$6.5 \times 10^{-5} \mathrm{~m}$
- D$12.4 \times 10^{-4} \mathrm{~m}$
Solution
From the relation
$\frac{I}{O}=\frac{v}{u}$
Here, $O=1.39 \times 10^9, v=0.1 \mathrm{~m}$,
$\begin{aligned}
u & =1.5 \times 10^{11} \mathrm{~m} \\
\therefore I & =\frac{0.1}{1.5 \times 10^{11}} \times 1.39 \times 10^9 \\
& =9.2 \times 10^{-4} \mathrm{~m}
\end{aligned}$
Hence, the correct answer is option: 'A'.