Question

An object $20cm$ from lens, has a virtual image at $10cm$ from the object. The power of the lens is

• A. $10$ diopters
• B. $-10$ diopters
• C. $5$ diopters
• D. $-15$ diopters

Answer 1

The correct option is C $5$ diopters

Here, $u=-20cm=-0.2m$

$v=10cm=0.1m$

$\therefore p=\frac{1}{f}=\frac{1}{v}-\frac{1}{u}=\frac{1}{-0.2}-\frac{1}{0.1}$
$P=-5+10=5$

Note that since power in diopters is to be calculated, all distance were kept in metres.