Question

A concave mirror forms a real image having the same sixe as the object at a distance of 40 cm in front of the mirror .What is the focal length of the mirror?​

Answer 1

hope this helps u

given ;-

  m =same size = -1 (real image m is -)

u = -40

v?

f?

solution

m = -v/u

-1 =  -v/-40 ( - and - get cancelled )

-1 = v/40

v= -40 cm

1/f = 1/v + 1/u

1/f = -1/40 -1/40

1/f = -2/40

-40/2f = 0

-40= 2f

f= -40/2

focal length  = -20cm

here we first find v inorder to get focal length by using 1/f=1/v+1/u

Answer 2

Answer:

Since focal length of concave mirrorgiven is 20cm l. Object is at 40cm distance which means it is at centre of curvature. hence, image will be formed of same size and at centre focus only but real and inverted.