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– Why does an ice cube melt in a warm
– Why does a cup of hot coffee cool off?
– How do they know the ambient
– This will happen even in a perfect vacuum
Judah Levine, 2170L11 9 Thermal Equilibrium - 2
All bodies continuously absorb and
emit energy as electromagnetic waves
– Emission proportional to temperature
– Thermal motion of charges in the material Body reaches thermal equilibrium
when incident energy balances emitted
energy Judah Levine, 2170L11 10 Body in thermal equilibrium
Incident energy is either reflected or absorbed
Absorbed energy is then used to drive the
The best emitter is therefore the best absorber
A perfect emitter would be a perfect absorber
A perfect absorber reflects nothing and is
A “black body” is the best possible emitter Judah Levine, 2170L11 11 Black Body spectrum - 1
Radiation is generated by thermal
motion of charged particles in the
Electromagnetic radiation caused by
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This note was uploaded on 01/29/2014 for the course PHYSICS 2170 taught by Professor Judahlevine during the Spring '13 term at Colorado.
- Spring '13