Question

When an object is placed at a distance of 27cm from a concave mirror, the size of the
image is three-fourth that of object.
i. Calculate the distance of image from the mirror?
ii. What will be the focal length of the mirror?​

Answer 1

Answer:

1= 20.25

Explanation:

I did not know the answer of the 2nd one

Answer 2

The distance of image from the mirror is 20.25cm.

The focal length of the mirror is 11.57 cm.

Given:

Object distance, u= 27cm  -(1)

Size of image to size of object, v/u = 3/4. -(2)

To find:

i) the distance of image from the mirror

ii) the focal length of the mirror

Answer:

The relation between focal length, object distance and image distance for a concave is mirror

1/f = 1/u + 1/v. -(3)

• From equation 1 and 2,

            v = 3u/4 = 3(27)/4 = 20.25 cm

• Substituting equations 1 and 2 in 3,

            1/f = 1/27 + 1/20.25

           ⇒1/f  = 0.08642

           ⇒f = 11.57 cm