Revise: Capacitor and Capacitance

Stores equal and opposite charge on two plates, separated by an insulator.

A camera flash charges slowly, discharges almost instantly.

C = Q/V, in farads.

Q=0.002C, V=100V → C=20μF.

C = ε₀εᵣA/d.

A=0.02m²,d=0.001m → C≈177pF.

E = ½CV² — grows with the SQUARE of voltage.

C=100μF, V=12V → E=7.2mJ.

Series: 1/C sums. Parallel: C sums directly (opposite of resistors).

4μF and 6μF in series → 2.4μF.

The insulating gap blocks any actual charge from crossing.

Used throughout electronics for storage, smoothing, timing.

Capacitance is a fixed property of the capacitor's own construction.

Real capacitors: μF or pF, rarely whole farads.

A dielectric material increases capacitance over vacuum/air.

A capacitive touchscreen senses a change in local capacitance.

Doubling voltage quadruples stored energy.

A defibrillator releases stored energy in a controlled pulse.

Series capacitors share the same charge; parallel share the same voltage.

Series combination raises the total voltage rating.