ALTERNATING CURRENT

I. When a coil is rotated through a constant B-field, an emf is induced in the coil. This emf varies with time, and for steady rotation at a constant angular speed, produces an emf that can be described by a sine or cosine.

II. If this ac generator is connected to a resistor, an alternating current is produced that is in phase with the voltage across the resistor.

III. If this ac generator is connected to a capacitor, an alternating current is produced that is out of phase with the voltage across the capacitor.

A. Use Kirchoff's Rule to show this.

B. For a capacitor, the current leads the voltage (ICE).

1. What is capacitive reactance?

IV. If this ac generator is connected to an inductor, an alternating current is produced that is out of phase with the voltage across the inductor.

A. Use Kirchoff's Rule

B. For an inductor, the voltage across the inductor leads the current (ELI).

1. What is inductive reactance?

V. What happens in a circuit with an ac generator, a resistor, a capacitor, and an inductor? (An RLC circuit)

A. Use Kirchoff's Rule

B. What is impedance?

C. How do things change if R = 0? (An LC circuit)

VI. Phasor diagrams can be used to sort out the phase relationships between voltages and currents in a visual way.

VII. How do you determine the power delivered when the currents and voltages vary with time?

A. What is the rms current?  the rms voltage?   How are they related to power?