Electronics

Inductor

A coil is a flywheel for charge. Drive it by hand and watch the electrons refuse to start, then refuse to stop, while the magnetic field they wind up stores every joule it takes to get them moving.

The balls are electrons and their speed is the current itself; nothing about them changes instantly

Current through the coil—

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Source

Drive it yourself 0.0 V

drag me up and down

Switch

Frequency —

slowfast

Resistor R 10 Ω

1 Ω1 kΩ

Turns N 200

Core µ_r 1

airiron

Coil area A 4.0 cm²

Time rate 1.0×

Fit a flyback diode across the coilShow the magnetic field

Values

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What to observe

Shove the source up. The electrons do not jump to speed, theyaccelerate, and while they do the coil takes almost the whole source voltage. Once the current is steady the coil voltage falls to nothing and it is just a wire.
Drop the source to zero with current flowing. The electrons keep going, and the coil voltage flips sign to push them on: it opposes the change, never the current.
Open the switch on a battery circuit. The current will not stop, so the coil makes hundreds of times the battery voltage and drives a spark. Tick the flyback diode and the spike vanishes.
On AC the current lags the voltage by a quarter cycle. Raise the frequency and the current shrinks, since X_L = 2πfL: the mirror image of the capacitor.

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