Electrical Sources

• There are two types of electrical sources. Alternating current (AC) sources provide an electrical signal that oscillates with time. Both the voltage and current in these signals oscillate from positive to negative values. An example of an AC electrical source is the power outlet found in homes. A direct current (DC) source provides an electrical signal that flows in a single direction, and at constant voltage. An example of a DC electrical source is a battery.
  
  

Voltage

• Voltage is a measure of the potential energy each electron in the current has (potential energy per unit charge). Reversing the polarity of a DC source will lead to a change in sign of the voltage on the biased device. The magnitude of the voltage remains the same. For example, if a battery is connected to a voltmeter and the positive terminal and negative terminals of the battery are connected to the same signed terminals on the voltmeter, then a positive voltage will be measured. However, if the polarity on the battery is reversed (leads on positive and negative terminal swapped), then a negative voltage will be measured.
  
  

Current

• Current is a measure of electron velocity, and is measured in terms of amps. Electrical current flows from the positive terminal to the negative terminal of a DC source. Reversing the polarity of a DC source will always lead to a change in current direction. The magnitude of the current will stay the same.
  
  

Electrical Components

• Caution needs to be exercised when reversing the polarity of a DC source. In general, the polarity cannot be reversed in complex circuits. Simple electrical components such as lamps, and DC motors will function fine when the polarity is switched. Sometimes this can be useful for DC motors, since the motor will run in the opposite direction when the polarity is switched. Other electrical components such as diodes, LED, and capacitors need to be connected in particular polarity in order to function correctly and avoid becoming damaged.