Question

A small piece of wire bent into an L shape, with upright and horizontal portions of equal lengths, is placed with the horizontal portion along the axis of the concave mirror whose radius of curvature is 10cm. I fthe bend is 20cm from the pole of the mirror, then the ration of the lengths of the images of the upright and horizontal portions of the wire is
A. `1:2`
B. `3:1`
C. `1:3`
D. `2:1`

Answer 1

Correct Answer - b.
For upright portion,
`m=(f)/(f-u)=((-10)/(2))/((-10)/(2)-(-20))=(-5)/(-5+20)=(-5)/(15)=-(1)/(3)`
For horizontal portion, magnification is `(-(1)/(3))^(2)` i.e., `(1)/(9)`
Required ration is `(-1//3)/(1//9)=-3:1`