Question

A $3cm$ high object is placed at a distance of $80cm$ from a concave lens of focal length $20cm$. Find the size of the image.

• A. 0.5 cm
• B. 0.6 cm
• C. 0.8 cm
• D. 1.2 cm

Answer 1

The correct option is B

0.6 cm

Here, $u=-80cm,f=-20cm$

Using the len's formula, $\frac{1}{v}-\frac{1}{u}=\frac{1}{f}$

$\frac{1}{v}-\frac{1}{-80}=\frac{1}{-20}$

$v=-16cm$

Magnification, $m=\frac{h^{{}^{\prime }}}{h}=\frac{v}{u}=\frac{-16}{-80}=\frac{1}{5}$

$h^{{}^{\prime }}=\frac{h}{5}=\frac{3.0}{5}=0.6cm$

Length of the image is 0.6 cm. Positive sign shows that the image is erect.