Question

An object 5cm long is placed 20cm from a concave lens of focal length 30cm. the size of image must be​

Answer 1

Explanation:

Formula:

$\frac{1}{v} + \frac{1}{u} = \frac{1}{f}$

Given;

$\frac{1}{v} + \frac{1}{ (- 20)} = \frac{1}{15}$

$\frac{1}{v} = \frac{7}{60}$

$v = \frac{60}{7}$

$v = 8.57 = 8.6cm$

The image is formed behind the mirror at a distance of 8.6 cm

$m = \frac{h1}{h2} = \frac{ - v}{u}$

$= > \frac{h2}{5} = \frac{( - 8.57)}{20}$

$= > h2 = 2.175cm$

Thus the image is 2.175 cm high, virtual and erect.

Hence, this is the answer.