A 10 cm long stick is kept in front of a concave mirror having focal length of 10 cm in such a way that the end of the stick closest to the pole is at a distance of 20 cm. What will be the length of the image?

Dear student,


Given,
f = focal length = -10 cm (concave mirror)
u = Object distance = -20 cm
1/f = 1/v + 1/u where v= Image distance
1/v = 1/f - 1/u 
       = (1/-10) - (1/-20)
       = (1/-10) + (1/20)
       = (-2+1)/20
       = -1/20
v     = -20

Given,
h1 = Object size = 10cm
h2 = Image size = ?
M(magnification)= h1/h2 = -(v/u) (concave mirror)
                                                 = -(-20/20)
                                                 = 1
h2 = 1*h1 = 1*10 = 10 cm 

Regards.