I^2 R Heating

The nichrome wire reaches temperatures exceeding 900°C (glowing red/orange). Do not touch the wire during operation or for several minutes after turning off current. Keep flammable materials at least 30cm away from the apparatus. Ensure adequate ventilation, especially if using the oiled string variation, as smoking oil produces irritating fumes.

Although voltage is relatively low (<15V), currents of 6-7A are significant. Ensure all connections are secure before energizing to prevent arcing or overheating at connection points. The power supply will dissipate significant heat at these current levels—ensure adequate ventilation around the supply and do not exceed its duty cycle rating (typically 5-10 minutes on, then cool-down period).

Purpose

Demonstrates Joule heating ( $$P = I^2R$$ ) by passing the same current through wires of different resistivity connected in series. Students see the high-resistivity wire glow red while the low-resistivity wire stays cool, illustrating why material selection matters in electrical applications.

Two ring stands with right-angle clamps supporting copper and nichrome wires connected in series between them, with a DC power supply on the bench displaying 15.6V and 6.7A

Figure 1: The demonstration setup shows copper wire (left) and nichrome wire (right) connected in series. At approximately 6.5A, the nichrome wire glows visibly red due to its higher resistivity, while the copper wire remains cool.

Copper and Nichrome Wire for 15V Power Supply

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Warning: High Temperature Hazard

Warning: Electrical Safety

Purpose

Safety Warnings

Warning: High Temperature Hazard

Warning: Electrical Safety

Purpose