Radiation Concept

Demonstrations in Radiation

Four photos: storage cabinet for the mirrors, a large parabolic mirror with a candle on a lab jack at its focal point, a parabolic mirror with a Crookes radiometer at its focal point, and an iron ball on a stand
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Parabolic Mirrors

Two parabolic mirrors at opposite ends of the lecture bench focus thermal radiation from a candle (or heated iron ball) onto a Crookes radiometer. Students see that radiant energy -- …
Two parabolic radiant heaters — a larger white modern unit and a smaller vintage chrome unit — on a lab bench
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Radiant Heater

Demonstrates radiative energy transfer — heat propagating through space without a medium. Use with a Crookes radiometer to visualize radiant energy, or with Leslie's cube to show how surface properties …
Small black-painted rectangular box with a hole in one end and a handwritten label on top
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Black Body

A black box with a small opening illustrates the cavity approximation to an ideal black body. Light entering the hole undergoes multiple internal reflections and is effectively absorbed, making the …
Crookes radiometer at rest: a clear glass bulb on an elegant glass stem and base, with four vanes (black on one side, silver on the other) visible inside
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Radiometer

Radiant energy transfer imparts motion: both visible and infrared radiation cause the radiometer vanes to spin. Students see a concrete example of electromagnetic energy converting to mechanical motion and observe …
Thermopile with rectangular reflector housing (right) and light-beam galvanometer with analog meter in a wooden carrying case (left), labeled P220.3
Safety

Thermopile

Detect and measure thermal radiation using a thermopile and light-beam galvanometer. The setup is sensitive enough to show the infrared radiation from a person's hand on the projection board, demonstrating …
Leslie's cube (black face visible, white funnel on top) mounted on a wooden stand with ruler scale. Two glass bulbs on metal arms extend to either side, connected by a U-tube with red liquid at the base.
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Leslie's Cube

Surfaces with different emissivities radiate different amounts of energy at the same temperature. The differential thermometer makes this visible: the fluid shifts toward the side receiving less radiation, showing that …
Two cylindrical cans with lids and dial thermometers inserted through the top: a silver/metallic can (left) and a black-painted can (right)
Safety

Radiation Cans

Two identical cans -- one black, one reflective -- filled with boiling water cool at different rates. The black can cools faster, demonstrating that high-emissivity surfaces radiate thermal energy more …
Absorption cell — a dark cylindrical cell on a stand with two mercury thermometers, one inserted through the cell and one mounted externally
Safety

Absorption Cell

Demonstrates that light carries energy by showing a thermometer inside an absorption cell reaches a higher equilibrium temperature than an external reference thermometer when illuminated. Provides direct evidence that electromagnetic …