The sun(diameter`D`)substance an angle`theta`radian at the pole of a concave mirror of focal length`f`.What is the diameter of the image of the sun formed by the mirror.

Explanation

Since the sun id very distant.u is very large and so`(1)/(u)`is practically zero.
`(1)/(u)~~0,(1)/(v)+(1)/(u)=(1)/(f)`
`(1)/(v)=-(1)/(f),v=-f`
The image of sun will be formed at the focus and will be real,inverted and diminished
`A B="height of image"`
`theta=("Arc")/("Radius")=(A'B')/(FP)`
`rArr theta=(d)/(f) ,d=f theta`