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•Hot objects glow (emit light)
–Heat (and collisions) in material causes electrons to
jump to high energy orbits
–As electrons drop back down, some of energy is
emitted as light.
–
•Reason for name “Black Body
Radiation”
–In a “solid” body the close packing of
the atoms means than the electron orbits are complicated, and virtually all energy orbits are
allowed. So all wavelengths of
light can be emitted or
absorbed. (In a gas with isolated
atoms, only certain orbits are permitted
so only certain wavelengths can be absorbed or emitted.)
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–A black
material is one which readily absorbs all wavelengths of light. These turn out to be the same materials which also readily emit
all wavelengths when hot.
–
•The hotter the material the more energy it
emits as light
–As you heat up a filament or branding iron, it glows
brighter and brighter
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•The
hotter the material the more readily it emits high energy (blue) photons
–As you heat up a filament or branding iron, it first
glows dull red, then bright red, then
orange, then if you continue, yellow, and eventually blue
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