Question

The sun subtends an angle of half a degree at the pole of a concave mirror which has a radius of cutvature of $15m$.Then the size(diameter) of the image of the sun formed by the concave mirror is

• A. $7.5cm$
• B. $6.55cm$
• C. $3.7cm$
• D. $13.1cm$

Answer 1

The correct option is B $6.55cm$

$\theta =\frac{diameterofsun}{distanceofsun}$$\theta =\frac{diameterofimage}{focallengthofconcavemirror}$
$\frac{1}{2}\times \frac{\pi }{180}=\frac{diameterofimage}{7.5m}$
$=\frac{3.14\times 7.5}{360}\times 100cm$
$=6.55cm$