Demos: 3D-01 Visible Radiation

A nichrome wire helix is held between two fixed insulating posts. The ends of the wire are connected to a Variac. When the Variac output is increased from zero, the resistance wire glows dull red, through orange, to yellow. (One can also observe linear expansion of the wire as it gets hotter.)

Directions: Just start with the Variac at zero voltage and slowly increase it until the wire starts to glow. If there is not a preset mark for maximum voltage, ask the demo technician.

Suggestions for Presentation: This is fairly straightforward. Students often associate hot wires with “heat”, not light. This is a reminder that both heat and light are just part of a continuum along the electromagnetic spectrum.

Applications: Any devices that, when, heated, give off visible radiation.

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