Fundamentals of Electricity
Electricity exists everywhere, from high voltage power lines to phones and computers. Understanding the basics of how it works remains essential to using it safely and efficiently.
At its core, electricity consists of the movement of electrons through a substance. Some materials, like copper and aluminum, allow electrons to flow much more easily. Furthermore, materials like rubber and ceramic resist electron flow and are said to have high resistance. Resistance, measured in units of Ohms, describes how easily electrons move through a material. An analogy for electron flow involves thinking of a pipe with water flowing through it. The diameter of the pipe equals the resistance.
Voltage (measured in units of Volts) is a measure of the “push” or the pressure of electrons being forced through the material. In the example of the pipe, voltage is the water pressure. Amperage, measured in units of Amps, is the resulting amount of electricity that passes through the material, or in the case of the pipe, the flow rate. These three quantities, Volts, Amps, and Ohms, are interconnected by the formula: V (volts) = I (amps) x R (ohms).
Assuming that resistance is fixed, increasing the voltage increases the amperage. In the case of a short circuit, resistance decreases to almost zero. If voltage remains constant, the amperage increases drastically.
Direct Current / Alternating Current
When electricity travels from a positive lead to a negative lead in a circuit powered by a battery, it is considered direct current. This type of current powers electronics, LED lights, and cars. Alternating current is generated from rotation, usually by a generator. The direction of the current and the voltage flips as the generator completes a rotation. The faster the generator spins, the faster the flipping of current direction occurs. In North America, the typical frequency of AC power is 60hz or 60 alternations per second. The advantage of AC power is that the voltage can be stepped up easily by use of a transformer, which allows high voltage transmission. AC power is also useful for electric motors.
Electricity and Power
Specifically, power is a measure of energy usage over time. The standard unit of power is the watt and calculated as P (watts) = V (volts) x I (amps). Utility companies sell electricity in units of kW*h (kilowatt hours), which is simply one kilowatt of power delivered continuously over one hour.
Any time current passes through a conductor, it generates a magnetic field. In the case of AC current, the value of the current increases constantly, then decreases, reversing direction. This constant change generates an oscillating magnetic field. If a conductor is wrapped in a coil, the magnetic field generated by each wrap of wire will form one continuous field. Any conductor that moves through a magnetic field will have voltage induced into it.
In the case of a generator, a conductor is moved through a field made from permanent magnets. In a coil of wire fed by AC, the magnetic field itself oscillates at the same frequency as the electricity that generated it. Therefore, a conductor placed in that field will have a proportional oscillating voltage induced in it – most noteworthy, and a basic concept of a transformer.
Inductance and Capacitance
When an alternating magnetic field is generated in a coil, the resulting field generates current in the coil itself and directly opposes the current that generated it. This is Faraday’s law of induction. In any system that uses a coil (motors and transformers) some power is lost to the coil’s own inductance.
Consequently, a charged conductor tends to produce voltage to oppose a change in voltage. The effect remains largest in a capacitor (a pair of plates separated by an insulator). In an AC circuit, capacitance directly counteracts inductance, essentially supplying power to the system that is lost to inductance.
Though electricity remains a broad and complex subject, these basics form the foundation of its understanding, usage and appreciation.