Question

A convex mirror with a focal length of 100 cm is used to form an Image. An object is placed 50 cm in front of
the mirror. Where is the image located?​

Answer 1

Explanation:

50 cm behind the mirror

Answer 2

Given :-

• Image distance = - 50 cm

As object distance is measured from the pole of the mirror

• Focal length = + 100 cm

Focal length of a convex mirror is positive

To find:-

• Image distance

Solution:-

By using mirror formula ,

⟹ 1 / f = 1 / v + 1 / u

here,

• f = focal length

• v = image distance

• u = object distance

⟹ 1 / 100 = 1  / v + 1 / (-50)

⟹ 1 / 100 = 1  / v - 1 / 50

⟹ 1 / v = 1 / 100 + 1 / 50

⟹ 1 / v = 1 + 2 / 100

⟹  1 / v = 3 / 100

⟹ v = 100 / 3

⟹ v = 33.3 cm

The image is formed at a distance of 33.3 cm behind the mirror

Points to remember :-

• Focal length of concave mirror is negative
• Focal length of convex mirror is positive
• Focal length of a convex lens is positive
• Focal length of concave lens is negative