Question

A real image (always inverted) is the one through which the

rays of light actually pass after reflection from concave mirror

and which can be formed on the screen. A virtual image

(always erect) is the one through which the rays do not actually

pass, although they appear to come from it. The position,

nature and size of the image of an object formed by a concave

mirror changes with the position of the object. The size of the

image may determine by using a graph paper fixed on the

screen

Object Image Nature of the

image

u = ∞ v = f Real, inverted and

highly diminished

∞ > > 2 2 < < ∞ Real, inverted and

diminished

u = 2f v = 2f Real, inverted and

same size 2 > > 2 < < ∞ Real, inverted and

enlarged

u = f = ∞ Real, inverted and

highly enlarged

f > u > 0 Behind the mirror Virtual, erect and

enlarged

i) When an object is placed at 30 cm in front of a

concave mirror, image of the same size is formed.

What is the focal length of the mirror?

ii) Differentiate between virtual image formed by a

concave mirror and of a convex mirror.

iii) A virtual, erect and magnified image of an object is to

be produced with a concave mirror of focal length 15

cm. What can be the object distance in this case?

iv) Irrespective of the position of the object, determine the

nature of the image formed by a concave mirror.​

Answer 1

When object is placed at center of curvature then image is formed at radius of curvature.

So the minimum distance is zero.

OR

Let focal length be f and and object is placed at u=2f

−f

1

=

v

1

+

u

1

=

v

1

+

−2f

1

v=−2f.

Image will form at object location.

So minimum distance is zero.