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Periscope
Mirror
 Periscope – The periscope uses paired mirrors set at 45° angles.
Periscope
A device using two mirrors that allows a person to see something at a different height or around
a corner. Periscopes are used in submarines and also during times of war to see across a field of fire without being directly exposed.
Phosphorescence
The way in which some materials glow when they are struck by
invisible waves such as ultraviolet light. (See also: Fluorescence and Luminescence.)
Photoelectric effect
The ability of some materials
to change light into electricity. Substances like selenium are especially useful in this respect, and they are used in photocells. Currently photocells are not efficient enough to produce more than the small amounts of power needed to run such things as calculators or space vehicles. It is hoped that, eventually, banks of photocells will be able to produce enough power to replace fossil fuels like oil and coal.
Photon
The basic source of light. It is a very tiny package of light energy. When a hot object releases a photon, we see it as a wave of light.
Pigment
A substance in the form of tiny particles suspended in a liquid that scatters certain kinds of light better than others (see: Scattering of light). Paint consists of a liquid (called a body) into which the pigment is mixed to produce the desired colour.
The size of the pigment particles is important. Tiny particles produce a glossy finish to paint, while larger particles give a matt finish.
Pink noise
Random noise in the range of 20
to 20,000Hz. The result is a hissing sound that drowns out all other kinds of sound. (See also: White noise.)
Pitch
Another word for frequency. (See also: Doppler effect of sound.)
Tube is cut away in front of the mirror.
Mirror
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