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The sun (diameter D) subtends an angle of \theta radians at the pole of a concave mirror of focal length \mathrm{f}.The diameter of the image of the sun formed by the mirror is

Option: 1

f \theta


Option: 2

\frac{f 2 \theta}{D}


Option: 3

2 \mathrm{f} \theta


Option: 4

\mathrm{D} \theta


Answers (1)

best_answer

Since the sun is at very large distance,
\mathrm{p=\infty}
\mathrm{\Rightarrow \quad \frac{1}{\infty}+\frac{1}{q}=\frac{1}{f}}
\mathrm{\Rightarrow \quad \mathrm{g}=\mathrm{f}}
If the diameter of the image be


\mathrm{\frac{d / 2}{q}=\alpha \quad \Rightarrow \quad d=(2 \alpha) q}
\mathrm{Putting \, 2 \alpha=\theta \: and \, q=f}
\mathrm{we\: obtain \: \quad D=f \theta}


 

 




 

Posted by

Rakesh

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