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.)
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.
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.).
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.)
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.
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.
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 anywhere on principle axis
Image is virtual & point sized
Numerical