Question

An object 4 cm tall is placed on the principal axis of a concave mirror of focal length 20 cm at a distance of 30 cm from it. find position, nature and size of the image.

Answer 1

Height (h) = 4cm
Since it is a concave mirror therefore f = -20cm
Object distance (u) = -30cm
v = ?
h' = ?
By mirror formula...
1/v + 1/u = 1/f
By putting the above values, we get
v = -60cm
Also, h'/h = -v/u
So we get h' = -8cm
Therefore, the image is real, inverted and magnified...



Hope it helps.....

Answer 2

h=4cm,u=-30cm,f=-20cm,v=?,h'=? 1/f=1/u+1/v. 1/-20=1/-30+1/v. 1/v=1/-20+1/30=-1/60 v=-60cm , image is real. m=h'/h=-v/u. h'=-v/u×h=-8cm