In case of a concave mirror, if an object is placed between the principal focus F and pole P of the mirror, which one of the following statements about the image is NOT correct?

Q: What is the answer to NDA (I & II) 2020 GAT Q150?

C. Correct — C, the image will be formed at infinity. When an object lies between the pole P and the principal focus F of a concave mirror, the image formed is virtual, erect and enlarged, and it lies behind the mirror. So statements (a), (b) and (d) are all correct; the one that is NOT correct is (c) — the image is not formed at infinity. (An image at infinity forms only when the object is placed exactly at the focus F.)

(a)The image will be virtual
(b)The image will be enlarged or magnified
(c)The image will be formed at infinity
(d)The image will be erect

Answer

Why

Correct — C, the image will be formed at infinity. When an object lies between the pole P and the principal focus F of a concave mirror, the image formed is virtual, erect and enlarged, and it lies behind the mirror. So statements (a), (b) and (d) are all correct; the one that is NOT correct is (c) — the image is not formed at infinity. (An image at infinity forms only when the object is placed exactly at the focus F.)

Why the others are wrong

(a)
The image will be virtual — This is a true statement, so it is not the answer: for an object between P and F the image is indeed virtual, formed behind the mirror.
(b)
The image will be enlarged or magnified — Also true — the virtual image formed is magnified, which is why a concave mirror is used as a shaving or make-up mirror; so it is not the incorrect statement.
(d)
The image will be erect — Also true — the virtual image is erect (upright), so this is not the incorrect statement either.

Concept

For a concave mirror the nature of the image depends on where the object is placed. With the object between the pole P and the focus F, the reflected rays diverge as if coming from behind the mirror, giving a virtual, erect and magnified image. This is the only object position for a concave mirror that produces a virtual image, and it is used in shaving and make-up mirrors.

The stem asks for the statement that is NOT correct. Three options describe the true image (virtual, magnified, erect); the odd one out is 'formed at infinity', which actually happens only when the object sits at the focus F.

Key facts

For a concave mirror with the object between the pole P and focus F, the image is virtual, erect and enlarged, and lies behind the mirror.
An image at infinity forms only when the object is placed at the focus F.
This 'between P and F' arrangement is used in shaving mirrors, make-up mirrors and dentists' mirrors.
As the object moves from P towards F, the magnified virtual image grows larger.

Concave mirror: image for different object positions

Object between P and F→image: virtual, erect, magnified, behind the mirror — NOT at infinity

Object at focus F→image at infinity (this is when 'at infinity' applies)

Statements a, b, d→all TRUE; statement c ('at infinity') is the one NOT correct

Between P and F the image is virtual, erect and magnified; 'formed at infinity' (c) is the false statement.

Study next

Image formation by a concave mirror for all object positionsUses of concave mirrors (shaving mirror, headlights, solar cookers)Image characteristics for a convex mirrorMirror formula and magnificationReal versus virtual and erect versus inverted images

Common traps

Confusing 'object at focus' (image at infinity) with 'object between P and F' (magnified virtual image).
Reading the 'NOT correct' stem carelessly and picking a true statement.

Given an object position on a concave mirror, identify the nature of the image, or the statement that does NOT fit.

Related PYQs

NDA_GAT_2024_II_Q892024Open & attempt →

A point object is placed at the centre of curvature of a spherical concave mirror. Which one among the following would be the correct location of image formed?

(a) At infinity
(b) At the centre of curvature
(c) At the focal point
(d) Between the focal point and the centre of curvature

Answer(b) At the centre of curvature

Same skill of locating a concave-mirror image from the object's position — here the object at C gives a real, inverted image at C, the complement of the 'between P and F' case.

NDA_GAT_2025_I_Q1262025Open & attempt →

An object is placed between infinity and the pole (P) of a convex mirror. The position of the image is

(a) between pole (P) and the focus (F), behind the mirror
(b) between the focus (F) and infinity, behind the mirror
(c) between the pole (P) and the infinity, in front of the mirror
(d) at the focus (F), behind the mirror

Answer(a) between pole (P) and the focus (F), behind the mirror

Companion mirror item — a convex mirror always gives a virtual, erect, diminished image between P and F behind the mirror, testing the same image-locating skill.

Practice

practice — not a real PYQ
A concave mirror forms a magnified, erect and virtual image when the object is placed
- (a)beyond C
- (b)at C
- (c)between P and F
- (d)at F
Answer(c) between the pole P and the focus F — as in a shaving mirror.
practice — not a real PYQ
For a concave mirror, an image at infinity is formed when the object is placed
- (a)at the focus F
- (b)at the centre of curvature C
- (c)between F and C
- (d)beyond C
Answer(a) at the focus F.