Parabolic reflector
A
parabolic reflector (also known as a
parabolic dish or a
parabolic mirror) is a
reflective device, formed in the shape of a
paraboloid of revolution. Parabolic reflectors can either collect or distribute
energy such as
light,
sound, or
radio waves.
The parabolic reflector functions due to the geometric properties of the paraboloid shape: if the angle of incidence to the inner surface of the collector equals the angle of reflection, then any incoming ray that is parallel to the axis of the dish will be reflected to a central point, or "
focus". Because many types of energy can be reflected in this way, parabolic reflectors can be used to collect and concentrate energy entering the reflector at a particular angle. Similarly, energy radiating from the "focus" to the dish can be transmitted outward in a beam that is parallel to the axis of the dish.
John Hadley introduced parabolic mirrors into practical
astronomy in 1721 when he used one to build a
reflecting telescope with very little
spherical aberration. Before that, telescopes used
spherical mirrors. The most common applications of the parabolic reflector are in
satellite dishes,
telescopes (including radio telescopes),
parabolic microphones, and many
lighting devices such as
spotlights,
car headlights,
PAR Cans and LED housings.
Parabolic reflectors suffer from an
aberration called
coma. This is primarily of interest in telescopes because most other applications do not require sharp resolution off the axis of the parabola.
The
Olympic Flame is lit using a parabolic reflector concentrating
sunlight.
A
mirage bowl or
parabolic mirror wok is a toy consisting of two parabolic mirrors that are put together like a
wok pan and a lid with a hole in it, gives the
optical illusion that something is on the lid, but actually it is at the bottom of the pan below.
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Parabola*
Parabolic trough*
Paraboloid*
Spherical reflector*
Solar Death Ray*
Java demonstration of a parabolic reflector*
Solar Energy Blog: See and discuss how concentrating solar energy is going to power our world in the not too distant future.
