Overview
Electric current is a flow of charged particles. This topic covers direct, pulsing and alternating currents, Ohm's law, the resistor, capacitor and inductor in a circuit, and impedance, and shows how cells and tissues behave in direct and alternating current.
Passive electric properties describe how cells and tissues behave in an electric field that is too weak to excite them. A tissue can be pictured as conducting fluids separated by cell membranes, which are poor conductors and act as tiny capacitors. A membrane has a capacitance of about 1 µF/cm².
Direct, pulsing and alternating current
In direct current (DC) charge flows in one direction at a constant value. Pulsing current keeps one direction but its value changes periodically, for example the rectified output of a mains supply or the pulses used in electrotherapy. Alternating current (AC) changes direction periodically; for a sinusoidal current i = I0 sin(2πft), with frequency f (mains: 50 Hz in Europe).
- Direct and Alternating Electric Current:
- Direct Current (DC): A unidirectional flow of charge, typically used in batteries.
- Alternating Current (AC): Periodically reverses direction, employed in transmitting audio and radio waves.