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 × 10^9 ~m and its mean distance from the earth is 1.5 × 10^ 11

Correct answer: A. 9.2 × 10^ -4 ~m From the relation (I)/(O)=(v)/(u) Here, O=1.39 × 10^9, v=0.1 ~m , aligned u & =1.5 × 10^ 11 ~m I & = 0.1 1.5 × 10^ 11 × 1.39 × 10^9 & =9.2 × 10^ -4 ~m aligned

NEET 2008

Exam: NEET
Year: 2008
Subject: Physics
Chapter: Ray Optics

NEET 2008 · Physics · Ray Optics

A boy is trying to start a fire by focusing sunlight on a piece of...

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?

Options

A $9.2 \times 10^{-4} \mathrm{~m}$
B $6.5 \times 10^{-4} \mathrm{~m}$
C $6.5 \times 10^{-5} \mathrm{~m}$
D $12.4 \times 10^{-4} \mathrm{~m}$

Correct answer

A. $9.2 \times 10^{-4} \mathrm{~m}$

Step-by-step 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}

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