Electronics

Resistor

Electrons pulled by the field and knocked back by the lattice, over and over. The average of that crawl is Ohm's law.

electronlattice ioncollision, heat handed over

The drift is drawn far larger than life; the numbers are the real ones

Resistance—

—

Plot under the scene

Material

Voltage across it 1.00 V

Length L 500 mm

short, easylong, hard

Cross-section A 0.10 mm²

thin, hardfat, easy

Ambient temperature 20 °C

Show

Thermal motionLet it heat itself upFollow one electron

Time rate 1.0×

Values for this metal

Resistance R—

Current I—

Power P—

Resistivity ρ—

Mean free time τ—

Drift speed v_d—

Thermal speed—

Thermal / drift—

What to observe

Turn thermal motion off and follow one electron: the field speeds it up, a collision resets it, over and over. The average velocity settles ataτ, proportional to the field, and that flat line is Ohm's law.
Double the length and the same voltage makes half the field, soR doubles. Double the cross-section instead and twice as many lanes carry the same drift, so R halves: R = ρL/A.
Heat a metal and the lattice shakes harder, τ falls and R rises. Carbon goes the other way, because heat frees more carriers than it scatters.
Let tungsten heat itself up at full voltage. It glows, its resistance climbs, and the I–V line bends over: a light bulb is only ohmic when it is cold.

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