Question

A concave mirror of focal length 15 cm forms an image of an object kept at a distance of 10 cm from the mirror. Find magnification produced by mirror 

Options

• 2
• 3
• 4
• - 3​

Answer 1

Answer :-

Magnification produced by the mirror is + 3 .

Explanation :-

We have :-

→ Focal length of the mirror = 15 cm

→ Position of the object = 10 cm

______________________________

Since, the mirror is concave :-

• f = - 15 cm

• u = - 10 cm

According to the mirror formula :-

1/v + 1/u = 1/f

⇒ 1/v = 1/f - 1/u

⇒ 1/v = 1/(-15) - 1/(-10)

⇒ 1/v = -1/15 - 1/10

⇒ 1/v = (-2 + 3)/30

⇒ 1/v = 1/30

⇒ v = 30 cm

______________________________

Now putting the values in formula of magnification, we get :-

m = -(v/u)

⇒ m = -(30/-10)

⇒ m = -(-3)

⇒ m = + 3

Answer 2

Given :-

A  concave mirror of focal length 15 cm forms an image of an object kept at a distance of 10 cm from the mirror

To Find :-

Magnification

Solution :-

We know that

1/f = 1/u + 1/v

1/-15 = 1/-10 + 1/v

-1/15 = -1/10 + 1/v

-1/15 + 1/10 = 1/v

-2 + 3/30 = 1/v

1/30 = 1/v

By reciprocal

30 = v

Finding magnification

m = hi/ho = -v/u

m = -v/u

m = -(30)/-10

m = 30/10

m = 3/1

m = 3