Sunday, December 27, 2009

Curved Mirrors

A curved mirror is a section of a sphere.
If the outside surface of the sphere is reflecting, the mirror is convex.
If the inside surface is reflecting, the mirror is concave.

The characteristics of the image formed can be
i. real or virtual
ii. inverted or upright
iii. larger , smaller or the same size of the object
By drawing ray diagrams, you can find out how the image would be.

Ray diagram --concave mirror1. Draw ray from top of object to the curved mirror. After reflecting off mirror, the ray passes through the focal point. (Purple ray)
2. Draw a ray from the top of the object through the focal point. The ray will be parallel to the optical axis after reflecting. (Green ray)
3. Draw the image as a vertical arrow with its tail on the principle axis and the head at the point where the two reflected ray meet.

Tips: Images formed "behind" the concave mirror are always upright and virtual.

Ray diagram --convex mirror

1. Draw ray parallel to optical axis. After reflection, this ray travels as if it is coming from the far focus. (Purple ray)
2. Draw line from top of object to centre ,C (Red ray).
3. The virtual image is drawn using a dotted line with an arrow.

Tips: Images formed by a convex mirror are always smaller that object.
Hand on :
Take the standard steel spoon in your kitchen, observe images formed at both side of the spoon at difference distance. What can you say about the image formed?


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