Question

An object is kept at a distance of 20 cm infront of a concave mirror the focal lenght of a mirror is 30cm find the image distance

Answer 1

u= -20 cm

f= -30 cm

$\frac{1}{u} + \frac{1}{v} = \frac{1}{f\\} \\=\frac{1}{-30}-  \frac{1}{-20}  = \frac{1}{v\\} \\=\frac{-2+3}{60} =\frac{1}{v}\\ \\=\frac{1}{60}= \frac{1}{v}\\\\=v=60$

Answer 2

Answer:

Explanation:

Solution,

Here, we have

Object distance, u = - 20 cm

Focal length, f = - 30 cm

To Find,

Image distance, v = ?

According to the mirror formula,

We know that,

1/f = 1/v + 1/u

1/v = 1/f - 1/u

So, putting all the values, we get

⇒ 1/v = 1/f - 1/u

⇒ 1/v = 1/- 30 - 1/- 20

⇒ 1/v = 1/20 - 1/30

⇒ 1/v = 3 - 2/60

⇒ 1/v = 1/60

⇒ v = 60 cm

Hence, the image will form 60 cm behind the mirror.