Resistivity and Temperature Concept

Demonstrations in Resistivity and Temperature

Iron wire coil on wooden stand with lower half submerged in water in a 4000-ml beaker, blue variac at left, empty beaker at right
Safety

Temperature Coefficient of Resistance

Demonstrates the positive temperature coefficient of resistance in metals. An iron wire coil glows uniformly at dull red; adding water to cool the lower half drops its resistance, increasing current …
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
Safety

I^2 R Heating

Demonstrates Joule heating 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 …
Iron wire coil assembly clamped to a ring stand with a flashlight bulb mounted on a wooden holder, BernzOmatic propane torch standing nearby, before heating
Safety

Iron Wire in Flame

An iron wire coil and a flashlight bulb are wired in series. Heating the coil with a torch until it glows red dramatically increases its resistance, visibly dimming the bulb. …
Two black-and-white photos of filament lamp circuits. Each shows a variac connected to a wooden board with a large filament lamp and a small indicator bulb wired in series. Top: tungsten lamp circuit with bulb lit. Bottom: carbon filament lamp circuit.
Safety

Carbon and Tungsten Lamps

Contrasts the temperature coefficient of resistance in two materials. A small indicator bulb in series with a carbon filament lamp brightens as the carbon heats (negative, resistance decreases). The same …