Question

Lens A produces a magnification of -0.8 whereas lens B produces a magnification of +0.8. Which one of the following applies to lenses A and B?

• A. Both A and B are convex lenses
• B. Both A and Bare concave lenses
• C. A is a concave lens and B is a convex lens
• D. A is a convex lens and B is a concave lens

Answer 1

The correct option is C A is a concave lens and B is a convex lens

Since we know that magnification m of lens is given by
$m=\frac{imagedistance}{objectdistance}$
$m=\frac{v}{u}$
in case of converging lens $\frac{v}{u}<0$ and in case of diverging lens $\frac{v}{u}>0$ as they are in same side of lens.And it is given that lens B has magnification+ 0.8 , hence it is a concave lens and lens A has a magnification of - 0.8 which means that it is a converging lens i.e. lens A is a convex lens and lens B is a concave lens.