INDUCTANCEBasic AC Reactive Componentswherep = ~3.14f = frequency (Hertz)L = inductance (Henries)The magnitude of an induced EMF in a circuit depends on how fast the flux that links the circuitis changing. In the case of self-induced EMF (such as in a coil), a counter EMF is induced inthe coil due to a change in current and flux in the coil. This CEMF opposes any change incurrent, and its value at any time will depend on the rate at which the current and flux arechanging at that time. In a purely inductive circuit, the resistance is negligible in comparison tothe inductive reactance. The voltage applied to the circuit must always be equal and oppositeto the EMF of self-induction.VoltageandCurrentPhaseRelationshipsinanInductiveCircuitAs previously stated, any change in current in a coil (either a rise or a fall) causes acorresponding change of the magnetic flux around the coil. Because the current changes at itsmaximum rate when it is going through its zero value at 90° (point b on Figure 1) and 270°(point d), the flux change is also the greatest at those times. Consequently, the self-induced EMFin the coil is at its maximum (or minimum) value at these points, as shown in Figure 1. Becausethe current is not changing at the point when it is going through its peak value at 0° (point a),180° (point c), and 360° (point e), the flux change is zero at those times. Therefore, the self-induced EMF in the coil is at its zero value at these points.Figure 1 Current, Self-Induced EMF, and Applied Voltage in an Inductive CircuitES-08 Page 2 Rev. 0

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