Question

I an object is kept at 20cm from a mirror fams its
image at same plane. Which type of mirror it is find its
focal length?

Answer 1

Answer:

Since the question has grammatical mistakes.

The question should be-

If an object is placed at a distance of 20 cm from mirror forms its image at same place. Which type of mirror it is find its focal length.

Answer is: it is concave mirror

Its focal length =10cm

Explanation:

Since from the question it is understood that the object is placed at Centre of curvature ( an imagery line that divides mirror into two equal parts ).

And we know that only the concave mirror can form the image on the point where object is kept

Hence, it is a concave mirror

And, for calculating its focal length we know that

F=R/2

(Where R is radius of curvature which is a line joining centre of curvature and pole where focus lies)

Hence

Focal length =20/2 cm

=10cm