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Capacitors - how they work!

Capacitors are very useful in electronics circuits they block direct currents and only allow alternating currents through them.

The capacitor has resistance to alternating currents and is called a capacitive reactance Xc.

Complex numbers are useful here to represent the capacitve reactance as a complex impedance in the cartesian form a + jb, where a represents pure d.c. resistance and jb is pure capacitve reactance. Because a capacitor is made up of two metal plates seperated by an insulator there is no d.c. resistance and the term for capacitve reactance is simply 1/jwc or -j/wc. (See Argand Diagrams)


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