Inductance

Basic Electrical Theory UNITS OF ELECTRICAL MEASUREMENT Using Ohm’s Law for the value of voltage (E), E = I x R and using substitution laws, P = I x ( I x R) power can be described as the current (I) in a circuit squared times the resistance (R) of the circuit. Equation (1-7) is the mathematical representation of this concept. P = I²R (1-7) Inductance Inductance is defined as the ability of a coil to store energy, induce a voltage in itself, and oppose changes in current flowing through it. The symbol used to indicate inductance in electrical formulas and equations is a capital L. The units of measurement are called henries. The unit henry is abbreviated by using the capital letter H. One henry is the amount of inductance (L) that permits one volt to be induced (V_L) when the current through the coil changes at a rate of one ampere per second. Equation (1-8) is the mathematical representation of the rate of change in current through a coil per unit time. (1-8) � � � � � � DI Dt Equation (1-9) is the mathematical representation for the voltage V_L induced in a coil with inductance L. The negative sign indicates that voltage induced opposes the change in current through the coil per unit time (DI/Dt). (1-9) V_L L^� � � � � � DI Dt Inductance will be studied in further detail later in this text. Capacitance Capacitance is defined as the ability to store an electric charge and is symbolized by the capital letter C. Capacitance (C), measured in farads, is equal to the amount of charge (Q) that can be stored in a device or capacitor divided by the voltage (E) applied across the device or capacitor plates when the charge was stored. Equation (1-10) is the mathematical representation for capacitance. (1-10) C Q E Rev. 0 Page 17 ES-01