A rod of length 10 cm lies along the principal axis of a concave mirror of focal length 10 cm in such a way that its end closer to the pole is 20 cm away from the mirror. The length of the image is,

Options

A. 2.5 cm
B. 5 cm
C. 10 cm
D. 15 cm

Answer

C

Explanation

By mirror formula, image distance of A
`(1)/(v)+(1)/(u)=(1)/(f),(1)/(v_(A))+(1)/(u)=(1)/(f)`
`(1)/(v_(A))+(1)/((-30))=(1)/((-10))`
`therefore v_(A) = - 15 cm`
Image distance of `C, v_(c ) = - 20 cm`
The lenght of image = `|v_(A)-v_(C )|`
`= |-15 + 20| = 5 cm`