Q.A rod of length 10cm lies along the principle axis of a concave mirror of focal length 10cm is such a way that the end closer to the pole is 20cm away from it. The length of the image is
(a) 5cm
(b) 10cm
(c) 15cm
(d) 20cm
Ans: (a)
Sol: Radius of curvature R = 20 cm
Let Rod AB =10cm lies along principle axis in which end A is the centre . Hence image of A is at A itself .
For end B ,
1/v + 1/u = 1/f
1/v -1/(-30) = -1/10
1/v = 1/30 -1/10 =-2/30
v= -15 cm
Length of image = 5cm