Basic Electrical Quantities

•Basic quantities: current, voltage and power

–Current: time rate of change of electric charge

  I = dq/dt 

1 Amp = 1 Coulomb/sec

–Voltage:  electromotive force or potential, V 

1 Volt = 1 Joule/Coulomb = 1 N·m/coulomb

–Power:  P = I V 

1 Watt = 1 Volt·Amp = 1 Joule/sec

•Active elements can generate energy

–Batteries

–Voltage and current sources

•Passive elements cannot generate energy

–Resistors

–Capacitors and Inductors (but CAN store energy)

An independent source (voltage or current) may be DC (constant) or time-varying, but does not depend on other voltages or currents in the circuit.

The dependent source magnitude is a function of another voltage or current in the circuit.