Capacitance
Adjust plates, see C change. Builds on Electrostatic Potential.
A parallel-plate capacitor is connected to a 12 V battery and fully charged. While the battery stays connected, you slowly pull the plates apart, doubling the distance between them.
What happens to the charge stored on the plates?
The charge drops to half! With the battery connected, the voltage is locked at 12 V. Doubling the distance halves the capacitance (C = ε₀A/d), so Q = CV also halves. Charge flows back through the circuit into the battery.
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Drag the plates apart and together while the battery is connected. Watch how charge flows back to the battery as you increase the gap. Toggle to ‘disconnected’ mode to see the difference — now charge is fixed but voltage changes!
C = ε₀A / d
Bigger plates and smaller gaps mean more capacitance. Q = CV ties it all together — but which variable is fixed depends on the circuit.
Your finger acts as one plate of a capacitor. Touching the screen changes the local capacitance, and the phone detects exactly where.
A capacitor charges slowly from a small battery, then dumps all its energy in a millisecond — that’s the bright flash.
Every bit in your computer’s RAM is a tiny capacitor. Charged = 1, discharged = 0. They leak and must be refreshed thousands of times per second.
A large capacitor charges to hundreds of volts, then discharges through the chest to restart the heart. Same physics, life-saving application.
“A capacitor is just two plates and a gap — but that simple geometry stores energy, drives camera flashes, and powers every touchscreen you’ve ever used.”
Capacitor Builder
Design your own parallel-plate capacitor. Adjust plate area, separation, and connection mode. Watch charge flow in real time and see how the electric field between the plates responds.
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Start with the battery connected and slowly pull the plates apart — watch charge drain back to the battery. Then disconnect the battery and try again: now the charge stays put but the voltage skyrockets. Try maximizing the plate area to see how much charge you can store at 12 V.
Capacitance is geometry. C = ε₀A/d tells you everything: big plates close together store the most charge. But whether Q or V adjusts when you change the capacitor depends entirely on what’s connected to it.