Question

An object of length $2.0\text{cm}$ is placed perpendicular to the principal axis of a convex lens of focal length $12.0\text{cm}$. Find the size of the image if the object is at the distance of $8.0\text{cm}$ from the lens.

• A. $4.0\text{cm}$
• B. $6.0\text{cm}$
• C. $8.0\text{cm}$
• D. $9.0\text{cm}$

Answer 1

The correct option is B $6.0\text{cm}$

We have,
$u=-8.0\text{cm}$
$f=+12.0\text{cm}$

Using,
$\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$

$\frac{1}{v}=\frac{1}{12}+\frac{1}{(-8)}$

$v=-24.0\text{cm}$

So,
$m=\frac{v}{u}=\frac{-24.0\text{cm}}{-8.0\text{cm}}=3$

$\therefore h_i=3h_o=3\times (+2.0)\text{cm}=+6.0\text{cm}$

The positive sign shows that the image is erect.