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Glossary P

Pauli Exclusion Principle
The principle that no two particles in
the same quantum state may exist in the same place at the same
time. Particles that obey this principle are called fermions;
particles that do not are called bosons.
Photoelectric Effect
Is the flow of electric current in a
material or through a vacuum (as in a photocell) when the material
is exposed to light. Although the effect itself had been known
for some time, Albert Einstein first described how it was caused
by absorption of photons, or quanta of light, in the interaction
of light with the electrons in the substance.
Photosphere
The layer of the Sun from which all visible
light reaches us. The Sun is too hot to have a solid surface and
the photosphere consists of a plasma at about 6000 degrees centigrade.
Pion
A Pion is a shortened form of the name
Pi meson; this subatomic particle comes in three forms: the pi-zero
(p0), pi-plus (p+) and pi-minus (p-). Pi mesons are the lightest
mesons. [more]
Plasma
A gas containing free ions and electrons,
and therefore capable of conducting electric currents. A “partially
ionized plasma” such as the Earth’s ionosphere is one that also
contains neutral atoms. The word plasma has a Greek root which
means to be formed or molded

Polar Orbit

A satellite orbit passing over both poles
of the Earth. During a 12-hour day, a satellite in such an orbit
can observe all points on Earth. Polar orbits are useful for viewing
the planet’s surface. As a satellite orbits in a north-south direction,
Earth spins beneath it in an east-west direction. As a result,
a satellite in polar orbit can eventually scan the the entire
surface. [more]
Plank’s Constant
Planck’s constant, denoted h, named after
the physicist Max Planck, is a physical constant which appears
in all quantum mechanical equations. Its value is approximately
h = 6.6261 × 10-34 Js [constants page]
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