Question

the focal length of a concave mirror is 20 cm find the position of the image of an object placed at the distance of 30 cm from the mirror​

Answer 1

Mirror Formula

→ 1/f = 1/v + 1/u

• f = Focal Length
• v = Image distance
• u = Object distance

→ 1/(- 20) = 1/v + 1/(- 30)

→ - 1/20 + 1/30 = 1/v

→ (- 3 + 2)/60 = 1/v

→ - 1/60 = 1/v

→ v = - 60 cm

Hence image is formed on left side [due to negative sign] 60 cm away from mirror.

v = - 60 cm

Answer 2

Given:

$\sf{f=20cm}$

$\sf{u=30cm}$

$\sf{Mirror=Concave \:Mirror}$

Solution:

From mirror formula:

$\sf{{\dfrac{1}{f}}={\dfrac{1}{v}}+{\dfrac{1}{u}}}$

$\sf{{\dfrac{1}{v}}={\dfrac{1}{30}}-{\dfrac{1}{20}}}$

$\sf{\dfrac{1}{v}}=-{\dfrac{1}{60}}$

$\sf{v=-60cm}$