 inductance of a circuit that will cause an induced emf of 1 V to be set up in the circuit when the current is changing at the rate of 1 A per second. Now the following relationship can be written: E1=LI/t, (A.18) where E1 is the induced emf; L is the inductance in henrys; I is the current in amperes; and t is time in seconds. If we have coils in series, then to calculate the total inductance of the series combina- tion, add the inductances such as we add resistances for resistors in series. In a similar manner, if we have inductances in parallel, use the same methodology as though they were resistances in parallel. A.7 INDUCTANCE AND CAPACITANCE Now distinguish between self-inductance and mutual inductance. Self-inductance is the property of a circuit which creates an emf from a change of current values when the reaction effects are wholly within the circuit itself. If the electromagnetic induction is between the coils or inductors of separate circuits, it is called mutual inductance. Capacitance. Capacitance was introduced in Section 2.5.1.1, during a discussion of its buildup on wire pair as it was extended. An analogy of capacitance is a tank of compressed air. Air is elastic, and the quantity of air in the tank is a function of the air pressure and capacity of the tank. Similar to Figure A.11, consider Figure A.12, which shows a capacitor connected across a battery emf supply. In its simplest form, a capacitor may consist of two parallel plates (conductors) separated by an insulator, in this case air. The circuit is equipped with an on-off switch. Close the switch. Unlike the inductance scenario in Figure A.11, there is a surge of current in the circuit. The current is charging the capacitor to a voltage equal to the emf of the battery. As the capacitor becomes charged, the value of the current decreases until the capacitor is fully charged, when the current becomes zero. A capacitor is defined as a device consisting of two conductors separated by an insu- lator (in its simplest configuration). The greater t