Figure 4 Inductors in Series

DC Circuits INDUCTANCE The induced EMF, or counter EMF, is proportional to the time rate of change of the current. The proportionality constant is called the "inductance" (L). Inductance is a measure of an inductor’s ability to induce CEMF. It is measured in henries (H). An inductor has an inductance of one henry if one amp per second change in current produces one volt of CEMF, as shown in Equation (3-1). CEMF = (3-1) L^DI Dt where CEMF = induced voltage (volts) L = inductance (henries) = time rate of change of current (amp/sec) DI Dt The minus sign shows that the CEMF is opposite in polarity to the applied voltage. Example: A 4-henry inductor is in series with a variable resistor. The resistance is increased so that the current drops from 6 amps to 2 amps in 2 seconds. What is the CEMF induced? CEMF L^DI Dt 4^� � � � � � 2A 6A 2 4( 2) CEMF 8 volts Inductors in series are combined Figure 4 Inductors in Series like resistors in series. Equivalent inductance (L_eq) of two inductors in series (Figure 4) is given by Equation (3-2). L_eq = L₁ + L₂ + ... L_n (3-2) Rev. 0 Page 3 ES-03