How is the Image Formed by a Spherical Mirror?
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.
Image Formed 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.
Fig. Concave mirror: object beyond centre of curvature, image between focus and centre of curvature. - 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.).
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.)
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.
Fig. 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.
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Image Formed by 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.]
Fig. Convex mirror: point object at infinity, virtual image at focus. - Object at anywhere on principle axis
Image is virtual & point sized.
Characteristics of the Image Formed by a Concave Mirror
Characteristics of the Image Formed by a Convex Mirror
Image Formed by a Spherical Mirror Experiment
Aim: To study the nature of images formed by convex and concave mirrors.
Materials needed: Concave mirror, convex mirror, a sheet of white paper, a well-lit window, and
adhesive tape.
Method:
For concave mirror
- Take the sheet of white paper and fold it about two or three times to make a screen.
- Stick the screen (folded paper) on the window grill of an open window.
- Take the concave mirror and hold it facing the window (and the screen).
- Move it back and forth till you get a clear image of the objects outside the window (such as leaves, trees, and sky) on the screen.
- Note down your observations for the following questions:
(a) Is it a real or a virtual image?
(b) Is the image inverted or upright?
(c) Is the image smaller or bigger than the object? - Look at yourself in the concave mirror and move the mirror forward and backward.
Note down your observations for the following questions:
(a) Is the image inverted or upright?
(b) Is the image upright when the mirror is closer to your face or farther away?
(c) Is the image of your face (when it is upright) smaller or bigger than your face?
(d) Is the image of your face (when it is inverted) smaller or bigger than your face? - Repeat the same procedure using a convex mirror and record your observations.