# A rod of length 10cm lies along the principle axis of a concave mirror of focal length 10cm is such a way that …..

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

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