Question

The sun (diameter $D$ ) subtends an angle $\theta $ radian at the pole of a concave mirror of focal length $f$ . The diameter of the image of the sun formed by the mirror is:

• A. $f\theta $
• B. $2f\theta $
• C. $\frac{2 f \theta }{D}$
• D. $D\theta $

Answer 1

Answer: (A)

Clearly Image distance is $v=f$
$tan\left(\frac{\theta }{2}\right)=\frac{A ' F}{P F}=\frac{A ' F}{f}A'F=f(tan\left(\frac{\theta }{2})\right)A'F=f(\frac{\theta }{2})A'B'=2A'F=f(\theta) $