Electrodynamics comprehensive notes

Electrodynamics

ALTERNATING CURRENT
 Voltage vs Time & Current vs Time
 Reducing the emf of a current
 Advantages of Alternating Current

IMPORTANT CONCEPTS DC MOTORS, AC GENERATORS
& DC GENERATORS
 Table comparing Energy conversion, Type of Current
used/produced, Structure, Function & Rules/Laws
applied and uses




Exam Guidelines




ALTERNATING CURRENT

AC generators produce an alternating current due to the fact that the current induced in the
coil/wires inside the generator is continuously changing direction and size. This change is best
illustrated in the Current vs time graph below:


Current vs Time Sine Graph

, 2




 The peaks in the current (both positive & negative) correspond to where the coil is moving at
90° to the magnetic field.
 When the coil is moving parallel to the magnetic field the current is ZERO.


The Voltage vs Time Graph (also a Sine Graph)
 South Africa’s electricity supply ranges between 220 V and 240 V (these values are not the
maximum values of the voltage produced, but are statistical averages of the voltage
supplied).
 This statistical average is described as the Root Mean Square or rms value.
 The Vrms (root mean square voltage) is smaller than the maximum voltage by a factor of
and has the following equation:

Vrms =

 Graphical representation follows below: