Image formation by Spherical mirror in Different Cases

Introduction : From mirror formula, we find that for a mirror of a fixed focal length f, as object distance u changes, image distance n also changes.

By Concave mirror :

Object at Infinity

A point object lying on the principal axis. Rays come parallel to the principal axis and after reflection from the mirror actually meet at the focus F.

The image is formed at F. It is real and point sized (fig.)

Object at infinity
Object at infinity

Fig. Concave mirror : point object at infinity, image at focus.

Object Beyond Centre of Curvature

Real object AB has its image A¢B¢ formed between focus and centre of curvature. The image is real-inverted and diminished.

Object Beyond Centre of Curvature
Object Beyond Centre of Curvature

Concave mirror : object beyond centre of curvature, image between focus and centre of curvature.

Read Also : Image Formation by Lenses

Object at Centre of Curvature

            Real object AB, has its image A¢B¢ formed at centre of curvature.

The image is real-inverted and has same size as the object. (fig.).

Object at Centre of Curvature
Object at Centre of Curvature

Concave mirror : object at centre of curvature, image at centre of curvature

Object between Centre of Curvature and Focus

Real object AB has its image A’B’ formed beyond centre of curvature.

The image is real-inverted and enlarged (bigger in size than the object). (Fig.)

Object between Centre of Curvature and Focus
Object between Centre of Curvature and Focus

Concave mirror : object between centre of curvature and focus, image beyond centre of curvature.

Object at Focus

Real object AB has its image formed at infinity.

The image is imaginary inverted (reflected rays go downward) and must have very large size.

Object at Focus
Object at Focus

Concave mirror : object at focus image at infinity.

Object between Focus and Pole

Real object AB has its image A’B’ formed behind the mirror. The image is virtual-erect and enlarged.

Object between Focus and Pole
Object between Focus and Pole

Fig. Concave mirror : Object between pole and focus, image behind the mirror.

By convex mirror

Object at infinity

A point object lying on the principal axis.

Rays come parallel to the principal axis and after reflection from the mirror, appear to diverge from focus F behind the mirror.

The image is formed at F.

The image is virtual and point sized. [fig.]

Object at infinity
Convex mirror : point object at infinity, virtual image at focus.

Object at anywhere on principle axis

Object at anywhere on principle axis
Object at anywhere on principle axis

Image is virtual & point sized

Numerical

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