A rod of length 10.0 cm lies along the principal axis of a concav mirror of focal length in such a way that the end closer to the pole is 20.0 cm away from it. The length of the image is :

Options

A. 10.0 cm
B. 15.0 cm
C. 5.0 cm
D. 20.0 cm

Answer

C

Explanation

(c ) As R = 20 cm. Position of end N is at centre of curvature so image N. is also formed at centre of curvature i.e. distance 20 cm from pole.

For end M, u = - 30 cm
`therefore (1)/(u) + (1)/(v) = (1)/(f)`
`therefore (1)/(v) = (1)/(u) - (1)/(u) = (-1)/(10) = (-1)/(15)`
`therefore` v = - 15 cm = distance of image of end M. ,
Thus lenght of image of rod = 20 - 15 = 5 cm.