Question

An object 3 cm high produces a real image 4.5 cm,when placed at a distance of 20 cm from a concave mirror.Calculate :(i) the position of image (ii) focal length of concave mirror.

Answer 1

Here
object height h1=3cm
image height h2=4.5cm
we know
m=h2/h1=-v/u
so,


4.5/3=-v /-20 (object distance =20)
4.5×-20/3=-v
v=30cm
so image is 30 cm from the mirror.
now , using mirror formula
1/u+1/v=1/f
1/-20+1/-30=1/f
-5/60=1/f
-1/12=1/f
f=-12
Hence , the required focal length is 12cm

Answer 2

Answer:

Hi for a real image in concave mirror is negative

Explanation: