Question

An object is placed at distance 2f from the pole of a convex mirror of focal length f . The magnification is?

Answer 1

Answer:

The magnification is 1/3

Explanation:

According to the problem the distance from mirror to object is 2f

and the focal length is f

Now, we know that

1/v+ 1/u =1/f [ v is the distance of image from mirror, u is the distance of object from the mirror and f is the focal length]

1/v+ 1/(-2f) =1/f

1/v=3/2f

v=2f/3

we know that magnification can be calculated:

height of  image/ height of object

magnification, m=2f/3/2f

                           =1/3

Answer 2

Answer:

Magnification :-    1/3

Explanation:

Given:

Object distance from pole (u): 2f

Focal length: -f  (focal length of concave mirror is negative)

From mirror formula

1/f=1/u+1/v

1/-f=1/2f+1/v  (given u=2f)

-1/v=1/2f+1/f

1+2/2f  = 1/v

3/2f   =  1/v

2f=3v

v=2f/3

m= height of image / height of object

m= 2f/3 / 2f

=1/3 (2f,2f get cancelled)