Question

An object is placed in front of a concave mirror at a very far distance. If the radius of curvature of the mirror is 18 cm, then the image of the object in front of the mirror will be formed at a distance of

With explanation​

Answer 1

Answer:

(9 × ♾)/(9 - ♾) cm

Explanation:

u = -♾

R = -18cm

f = R/2 = -9cm

1/f = 1/v + 1/u

1/-9 = 1/v + 1/-♾

-1/9 = 1/v - 1/♾

1/v = -1/9 + 1/♾

1/v = (9 - ♾)/(9 × ♾)

v = (9 × ♾)/(9 - ♾) cm

Answer 2

Given: An object is placed in front of a concave mirror at very far distance. Radius of curvature is 18 cm.

To find: Position of image formed

Explanation: Since the object is placed very far from the mirror, it is assumed that the object is placed at infinite distance from the pole of the mirror. Therefore, 1/u= 0 because 1 divided by infinite tends to zero.

Radius of curvature= 18 cm

Focal length= Radius/2 = 18/2

= 9 cm

But since it is a concave mirror whose focal length is always negative we take the focal length to be -9 cm.

Now, using mirror formula:

1/v + 1/u = 1/f

=> 1/v + 0 = -1/9

=> 1/v = -1/9

=> v = -9 cm which is also the focal point of the mirror

Therefore, the image of the object in front of the mirror will be formed at a distance of 9 cm on the focal point of the mirror.