Question

It is desired to obtain an erect image of an object, using concave mirror of focal length of 12 cm.
(i) What should be the range of the object distance in the above case?
(ii) Will the image be smaller or larger than the object? Draw a ray diagram to show the formation of image in this case.
(iii) Where will the image of this object be, if it is placed 24 cm in front of the mirror?

Answer 1

1. Ans.:- Range of the object should be between Pole and Focus because Concave mirrors forms an errect image when object is kept between Pole and Focus
2. The image will be larger than the object.
3. u = -24 cm

f = -12 cm

By using mirror formula;

1/f = 1/v + 1/ u

-1/12 = 1/v + (-1/24)

-1/12 = 1/ v - 1/24

-1/12 + 1/24 = 1/ v

(-2 + 1)/24 = 1/v

-1/24 = 1/v

V = -24 cm

Another way to get answer of third ques.

Focal length:- 12 cm

Object distance ( u ) :- 24 cm

It means that object is kept at on the center of curvature, and when object is kept at center of curvature (C)

• img.dis (v) = obj.dis (u)
• height of the img. (hi) = height of the object (ho)