Define the following terms:

Pls. post each query seperately.

Mirror - A reflecting surface generally made of glass with a mettalic or amalgam backing and set in a frame.

Lens - An optical device that bends transmitted light by refraction.

Virtual and real image - If a pencil of rays diverging from a point is caused by reflection or refraction to converge or diverge from other point, this second point is called the image of first point. If the rays of light actually pass through the second point, the image is said to be real but if they only appear to do so the image is called virtual.