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An Introduction to Electricity
In this page of introduction chapters, understand the concept of how electricity that powers our everyday devices by learning about fundamentals of electrical engineering and circuit analysis needed for trade skills professions.
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Looking for more? View information on the following chapters here:
Chapter 5: Types of Electric Circuits
Chapter 6: Switches & Loads
Chapter 7: Circuit Components
Chapter 1: An Introduction to Electricity
Understanding Electricity
All elements are made up of atoms. Atoms are made up of even smaller particles: the nucleus is includes protons, which have net positive charge; the electrons of an atom are negatively charged. This positive nucleus attracts the negative electrons, which orbit the nucleus because of a force called electromagnetic force.
The outermost electrons of an atom are valence electrons. They require the least energy to be released from an atom’s orbit. If an electromagnetic force releases an electron from orbit around an atom, it becomes a free electron that can move from atom to atom to create electricity.
Electricity is a form of energy. When you pass electricity through different materials, they behave differently. For example, electricity can be used to heat up a filament wire in an incandescent light bulb or make materials vibrate at a specific frequency to produce sounds.
Conductors & Insulators
Conductors are materials that are better able to conduct electricity since they allow electrons to move more freely. Metals are typically very good conductors and thus have a high conductivity. Pure silver is the most conductive of the metals but is also quite expensive. Copper is the next best conductor and is used for much of the wiring in our daily devices. Even humans are excellent conductors, which is why you can shock yourself.
In contrast, insulators are materials that block electricity, as they strongly resist releasing free electrons. The best insulators are non-metals, like rubber, cotton, glass and especially plastics and ceramics. Insulators are often used to ensure that electricity only flows along the intended paths. Insulators are also used for electrical protection, like sheathes on power cables. Both conductors and insulators are used in devices as a part of circuits.
Chapter 2: Introduction to Circuits
What is a circuit?
Electricity is defined as a flow of electrons that have been forced to move between atoms. For the electrons to move and produce electricity, there needs to be a complete circuit. The closed path that these electrons follow is called an electric circuit.
Circuits make up every device's electrical engineering. There are many different kinds of circuits, like resistive circuits or parallel circuits. The most basic elements of circuits consist of a voltage source, a load, and wires connecting them. A classic example is a battery (voltage source), connected through wires, to a light bulb (load).
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An electric circuit in a device can be compared to the human circulatory system:
Wires in an electric circuit can be thought of as blood vessels in the circulatory system. Wires carry electricity through the electric circuit like how blood vessels carry blood through the circulatory system.
The heart creates a pressure that pumps blood through the veins. Similarly, voltage sources create ‘pressure’, or voltage, in an electric circuit. A battery provides voltage and current through wires to different loads. This makes the light bulb glow.
Providing electric energy through voltage and current to loads using a source is the main objective of a circuit. Loads can be any device that requires electricity to work, like light bulbs, fans, clocks, stoves, etc.
Because electrons are negatively charged, they travel from the negative terminal of the source through the circuit to the positive terminal. If the current’s path is broken, the circuit becomes an open circuit. In this steady state, the electrons have no path to follow, and no electric power can be delivered to the load. If the current’s path is complete, the circuit becomes a closed circuit. In this steady state, the electrons can travel from the negative to the positive terminals of the source. Electric power can be delivered to the load in a closed circuit.
Operating Principles
The ability or potential to push electrons in a circuit is called voltage, measure in volts (V). Batteries are a common voltage source and can create current in a circuit. Voltage and current are very important to understanding electrical energy.
Current (I) is the rate at which electrons flow through a conductor. The unit of measurement for current is the ampere, or amps (A). Higher voltages create bigger currents.
Often times, voltage and current within a circuit must be managed by resistance. Resistance (R) is the opposition to the flow of electric current. It varies depending on the material and its shape and is measured in ohms (Ω).
Voltage, current, and resistance all come together to make a circuit work. A voltage source connected to a circuit will cause a current to flow, which will offer resistance to the flow. To turn the circuit on or off, we can use a switch.
Simple Circuits
At a minimum, the following 4 elements make up the engineering of a simple circuit:
A voltage power source supplies electric power to the circuit (ex: battery).
Wires provide an electric path for voltage and current to pass through and connects all elements in the circuit.
The device in a circuit that consumes power is called load (ex: light bulbs, electric motors, electric heaters).
A switch is a device that opens or closes the circuit and can be connected anywhere between the connected terminals (ex: light switches or the slide switch on your flashlight).
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Any circuit can be made using an energy source, wires, a load, and a switch for ease of operation. Circuits can then be used for various devices to be powered using electricity.
Chapter 3: Basics of Circuits
Additional Operating Principles
Keep in mind that the movement of electrons can cause a material to become either positively or negatively charged. If an object has extra electrons, it will have a negative electric charge. If an object has lost electrons, it will have a positive electric charge. Objects with opposite charges attract, while objects with like charges repel.
Electric charge (q) is measured in units of Coulombs (C). One Coulomb is equal to the amount of charge carried by more than 6-quintillion electrons (1C = 6.2415 x 1018 electrons).
The ability of a material to hold an electric charge is called capacitance (C). This ability is present in every object, like our bodies, balloons, plastic items, and styrofoam. It is measured in units of farads (F). Most items have a relatively small capacitance represented in microfarads (μF), where 1F = 1,000,000 μF.
Any time current flows through a conductor it creates a directional magnetic field (B) around that conductor. The process of magnetic fields inducing voltage and current is called inductance (L) measured in Henrys (H). This occurs as magnetic fields can create a voltage in any conductor that is exposed to them, inducing a current flow.
A circuit that has voltage and current flowing is transferring electrical energy. This transferred energy can be represented in units of time, which we call electric power or wattage. Power (P) is measured in units of Watts (W).
Basic Components of Electrical Circuits
The basic electrical components used in the engineering of all electrical circuits used in your devices can include some or all of the following:
Conductors
Insulators
Resistors
Capacitors
Inductors
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Resistors are electrical components designed with a specific amount of resistance used to limit the voltage and current in a circuit, like in resistive circuits or RC circuits. They are passive components, meaning they can only consume power. Adding a resistor to the circuit will reduce the amount of current flowing through a load to prevent damage. The size in ohms of a resistor will determine how much current flows. If too small, the current can still be too high. If too big, the current might not be enough to power the load.
While some circuits (namely resistive circuits) may not contain capacitance or inductance, they are typically fundamental components of electrical circuits. Capacitors are electrical components that work by having a metal plate connected to each of the terminals. These plates are separated inside the capacitor by non-conductive material. An electric field is created between the plates, which stores voltage for a short time.
Inductors provide energy storage in a magnetic field. This energy storage can be used to prevent sudden changes in current flow. The size in Henrys of an inductor will depend on the thickness of the wire used and the number of turns the coil has.
AC vs. DC Current
There are two types of electric current:
Alternating Current (AC) - current where electrons flow in both directions
Direct Current (DC) - current where electrons only flow in one direction
AC is usually preferred for long distance transmission because it has less power loss over long distances. DC energy can be stored, for example in batteries, but AC energy cannot. An example of an AC circuit is a resistive circuit, while an example of a DC circuit is parallel circuit.
Chapter 4: Introduction to Circuit Analysis
Circuit Analysis
Circuit analysis is the process of solving the elements within a circuit in electrical engineering. This type of analysis includes finding voltage and current within each element. In this chapter, we will cover Ohm's Law and Watt's Law as brief methods of analysis within circuit analysis.
Ohm’s Law
G. S. Ohm was a German physicist who discovered and published Ohm's Law. He discovered that electricity behaves like water in a pipe. When pressure increases, water flows faster; similarly, when voltage and current increases. Blockages in the pipe restrict water flow the same way that resistances reduce current flow. Thus, Ohm's law states that voltage and current in a circuit are directly related, but inversely related to the resistance.
This means that when voltage (V) is increased or reduced, the current (I) increases or is reduced accordingly. If resistance (R) is increased or reduced, voltage and current is reduced or increased accordingly. This is represented in the following formulas:
V= I * R
I = V ÷ R
R = V ÷ I
In this method of analysis, you can determine any one component when problem solving as long as know the other two components.
A resistor with a varying resistance is called a potentiometer. If you vary the resistance in a circuit that turns on a light, you can control how much voltage and current flows through it. By doing this, you can choose how bright the light glows.
Watt’s Law
James Prescott Joule was an English mathematician and physicist. His work with steam engines led to his discoveries in the relationship voltage and current has with electrical power.
Watt’s Law states that the power in an electrical circuit is the product of voltage and current. This results in the following formulas:
P = I * V
V = P ÷ I
I = P ÷ V
In this method of analysis, you can determine any one component when problem solving as long as know the other two components. A methodology combining the use of Ohm's Law and Watt's Law can allow you to determine measures of power, resistance, voltage and current within a circuit.
Want to Learn More?
View our page covering more fundamentals of electrical engineering for the trades:
Chapter 5: Types of Electric Circuits
Chapter 6: Switches & Loads
Chapter 7: Circuit Components