concave mirror

A concave mirror is a spherical mirror whose reflecting surface curves inward, like the inside of a bowl.

• Held close to a face, a concave mirror shows an enlarged, upright image — move the object farther away, and the image flips upside down while shrinking back down in size.
• This mirror is made by coating the outer curved surface of a ground glass piece with a reflective layer, so light bounces off from the inside of the curve.
• Concave mirrors converge parallel light beams to a single point, which is exactly why torch and headlight reflectors, dentist's mirrors, and the main mirrors of reflecting telescopes all use this shape.
• That same converging power lets a concave mirror focus sunlight into a small, intensely hot spot — strong enough to make paper smoke or even catch fire, the same principle behind solar cookers and solar furnaces.