Resistance Topic

Resistance Characteristics

Concept 3 demos

Collection of resistors and passive components including color-banded carbon and metal film resistors of various wattages, wire-wound resistors (one labeled Super Davohm), white ceramic power resistors, small black potentiometers, disc capacitors, and a wire-wound inductor

Resistors

Displays a collection of resistor types — wire-wound, ceramic, and color-banded carbon/metal film — so students can see how resistance is physically implemented. Illustrates that physical size correlates with power …

Demo multimeter (3B U21100) with large LED display reading 4.3 Ω, positioned above a wire-wound slide-wire rheostat with sliding contact near the left end

Variable Resistor

Shows that resistance scales linearly with conductor length using a wire-wound rheostat and demo multimeter. Students observe direct evidence for by sliding a contact along the resistor and watching the …

Two yellow digital multimeters connected to a cylindrical wire-wound variable resistor and 6V Energizer battery; left ammeter reads 36.8 mA, right voltmeter reads 5.93 V

Resistance

Students observe that resistance is directly proportional to conductor length by varying the effective length of a wire-wound variable resistor. Simultaneous voltage and current measurements allow real-time calculation of at …

Resistivity and Temperature

Concept 4 demos

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

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

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

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. …

Conduction in Solutions

Concept 2 demos

60W incandescent bulb on ceramic socket base (unlit) connected by wires to a glass tank with copper plates draped over opposite short sides, filled with clear water

Salt Water Circuit

Students see that tap water alone cannot carry enough current to light a bulb, but adding salt provides mobile ions that enable conduction. Increasing salt concentration increases brightness, showing the …

Pickle glowing bright yellow-orange on a sheet of paper, with nail electrodes and alligator clip leads attached

Glowing Pickle

AC current passed through a pickle causes it to buzz and glow bright yellow. Students see ionic conduction in action and observe the characteristic sodium D-line emission (589 nm) produced …

Conduction in Gases

Concept 5 demos

Adjustable spark gap with two rod electrodes on a stand, red cables attached, a small blue spark visible between the electrode tips

Spark--Gaps

Spark gaps provide a simple method to estimate high voltage from electrostatic generators. By measuring the gap distance at which breakdown occurs, students connect electric field strength to dielectric breakdown …

Two views of Cottrell smoke precipitator chambers. Top: cylindrical glass chamber with central electrode on a dark wooden base. Bottom: similar chamber showing vertical pin electrodes arranged in a circle inside the clear cylinder.

Smoke Precipitators (Cottrell)

Demonstrates electrostatic precipitation (Cottrell process). High voltage from a Van de Graaff generator ionizes air inside a smoke-filled chamber; the ions attach to smoke particles, which then migrate to the …

Heathkit regulated power supply with projection meter on top, incandescent bulb wrapped in aluminum foil on a small base, and variac on a lecture bench

Edison Effect

Demonstrates thermionic emission (the Edison effect): a heated filament emits electrons that flow toward a positively charged external electrode, but current does not flow when polarity is reversed. Students observe …