Question

Find the position, nature and size of the image of an object 3 cm high placed at a distance of 9 cm from a concave mirror of focal length 18cm.

Answer 1

Here, the image `"position"//"distance", v=?`, image size, `h_(2) =?`, object size, `h_(1)=3cm`
object distance, `u = -9cm`
Focal length of concave mirror, `f= -18cm`
As `(1)/(v) + 1/u = (1)/(f), :. (1)/(v) = (1)/(f) - 1/u = 1/-18 + 1/9 = (-1+2)/(18)=1/18`
`v=18 cm`
Positive sign of v shows that the image is virtual.
Again, `(h_(2))/(h_(1)) = -v/u` or `(h_(2))/(3) = (-18)/(-9) =2` or `h_(2) =6cm`
Positive sign of `h_(2)` shows that the image is erect. Obviously, it is magnified.