Question

III.
A concave mirror forms a virtual image of an object placed at a distance 20 cm. If the size of
the image is twice of the size of the object then the image will be formed at a distance (1)
a) 10 cm
b) 30 cm
c) 20 cm
d) 40 cm​

Answer 1

Answer:

here u got ur answer its 10 cm

Answer 2

Given:

• Concave mirror forms virtual image.
• Object distance is 20 cm.
• Size of image is 2 times the size of object.

To find:

Image distance ?

Calculation:

• For any mirror, we know that magnification can be written as:

$\therefore \: mag. = \dfrac{h_{i}}{h_{o}} = - \dfrac{v}{u}$

$\implies 2= - \dfrac{v}{u}$

$\implies v = - 2u$

• Now, putting value of 'u':

$\implies v = - 2\times (-10)$

$\implies v= 20$

• Positive sign denotes that image is virtual

So, virtual image is formed at 20 cm from mirror [OPTION c) is correct ✔️]