Question

An object is placed at a distance of $10cm$ from a convex lens of power $5D.$ The position of the image is

• A.
  $-20cm$
• B.
  $40cm$
• C.
  $45cm$
• D.
  $-10cm$

Answer 1

The correct option is A

$-20cm$
$u=-10cmP=5Df=\frac{1}{P}=0.2m=20cm$

$\Rightarrow$ Using lens formula

$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$
$\frac{1}{v}=\frac{1}{20}-\frac{1}{10}$
$\frac{1}{v}=-\frac{1}{20}v=-20cm$