## Tuesday, June 21, 2016

### 2.5-6 Using AC/ DC, and Measuring

This is the fifth week of Module 2 of the Navy Basic Electricity and Electronics series. The last few weeks were:

2.1 Electromotive Force
2.2 Magnetism
2.3 Electromagnetic Induction
2.4 Generating AC Voltage

2.5 Uses of AC and DC
 Fig 1: alternator
A generator is a machine that converts mechanical energy to electrical energy. Generators that produce AC are often specifically called alternators. From the previous section, you take the rotating loop in the magnetic field (the armature). Then they can be connected to "slip rings" that rotate with the armature. The slip rings make contact with stationary carbon brushes that are connected to a circuit (see Fig. 1).

If, in place of slip rings, a "commutator" is set up, DC current can be produced. The brushes are placed in such a way that positive or negative voltage is always coming out of a specific brush (see Fig. 2).

Voltage can be increased or decreased by the use of a transformer. Also, the power supplies in devices like radios and televisions convert the AC from the wall plug to DC. AC is more economical to transport over long distances and is more efficient for driving motors. DC needs to be used in electronic equipment where the voltage change might be harmful to the operation of their circuits.

2.6 Measuring Voltage
1. Voltage is measured in volts, with the symbol V. (Remember from the first module that current is measured in amps, with the symbol I. One amp is one coulomb's worth of electrons passing any one point per second, with Q as the symbol for coulombs.) Voltage is a measure of the "difference in potential" between two points in a circuit.

Just as an ammeter measures current (connected in series so that all the current goes through it), a "voltmeter" measures voltage. It needs to be connected in parallel or across two points in a circuit. It should be connected to "observe polarity," that is, the positive jack of the voltmeter (red) connected toward the positive side of the circuit and the negative jack (black) connected toward the negative side.

The symbol for a voltmeter is a circle with a V in it. Make sure you have the voltmeter set to the range of voltage you are measuring.

2. Voltage is not exactly the same as EMF (electromotive force), but you can measure a potential difference where there is an EMF generated (voltage rise), like if you were to place the leads across a battery. You can also measure a potential difference where voltage is being used (voltage drop), such as across a "load" such as a light bulb.

A load is a term for anything in a circuit that uses the energy produced by the circuit's source (e.g., a battery).

Here endeth the second module.