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An Introduction to Electricity & Circuits

Electricity Fundamentals: Chapter 1

An Introduction to Electricity

In this module, we will introduce what electricity is and briefly cover its history. Then we will explore what makes something an electrical conductor or an insulator. Skip to quiz!

Brief History

Have you ever shocked yourself when touching a doorknob? Or had styrofoam particles cling to you? That shock and the cling of styrofoam are two examples of electric charge. There are many examples like this in nature that led to the discovery and study of electricity.

Nowadays, electricity is everywhere. It is used for lighting, heating, refrigeration, and operating appliances. Another modern use is in electric vehicles and public transport.

Two of the largest uses of electricity are for:

  • HVAC systems in the residential sector, and

  • Office electronics in the commercial sector


To understand electricity, we first need to understand that all elements are made up of incredibly small atoms. Atoms are made up of even smaller particles, including electrons, which are very important for electricity.

The nucleus is where the protons are and has a net positive charge. The electrons of an atom are negatively charged. This positive nucleus attracts the negative electrons, which orbit the nucleus like how planets orbit the sun.

Planets orbit the sun because of gravitational force. Electrons orbit the nucleus of atoms because of a force called electromagnetic force. Electromagnetic force is also what causes electrons to flow, making electricity.

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. Free electrons can move from atom to atom.

Electricity is defined as the flow of electrons, specifically free electrons. If an electron is forced to move from one atom to another, electricity is produced.

How do we produce electricity that can be used for our appliances and devices? The most common way to generate electricity is by using turbines to power an electric generator.

Like pinwheels that spin when you blow on them, turbines need a force to turn.

Turbines can be powered by:

  • Burning fossil fuels, such as coal or oil, to create steam,

  • Using nuclear power to create steam, or

  • Using renewable sources, like wind or water

How does electricity power our devices? Recall that electricity is a form of energy, just like how heat and light are forms of energy. When you pass electricity through different materials, they behave differently.

One use of electricity is heating up a filament wire in an incandescent light bulb. By heating up the filament wire to a hot enough temperature with electricity, it will start to glow.

Another example of using electricity is to make materials vibrate. Electricity can make some materials vibrate at a specific frequency to produce sounds. This property of vibration is used in speakers and microphones.

Electricity can be lethal to humans. Electrical burns can damage skin and organs, or electric shocks can stop the human heart.

In addition to electrical shock and burns, electricity can cause fires or explosions. The three main dangers of electricity are:

  • Electrical shocks

  • Electrical burns

  • Fire and explosions


To transfer electricity from where it is produced to our cities and homes, it needs to be carried by wires. Likewise, inside our devices there are circuits carrying electricity to components that need power. High voltage power lines and the power cord for your toaster are both made of conductors.

Recall that electromagnetic force can make free electrons flow from one atom to another to produce electricity. Electrons can move easily in conductors. This makes conductors better able to conduct electricity.

Lots of materials are good conductors of electricity, but some are better than others. Metals, for example, are typically very good conductors and thus have a high conductivity. Even humans are excellent conductors, which is why you can shock yourself.

Some of the best conductors are copper, aluminum, gold, and silver. Pure silver is the most conductive of the metals but is also quite expensive. As such silver is generally only used for the surface of contacts. After silver, copper is the next best conductor and is used for much of the wiring in our daily lives.


If metals like silver and copper make the best conductors, what are the worst conductors Materials like rubber, plastic, and glass are well known for blocking electricity. These materials are called insulators, and they resist the flow of electricity.

Recall that electricity needs the flow of free electrons which have been released from individual atoms. Insulators are materials that strongly resist releasing free electrons. So no electrons are available to flow and produce electricity. The best insulators are non-metals, especially plastics and ceramics.

Insulators can also be used in circuit boards and other small electronics to ensure electricity only flows along the intended paths.Insulators can also be for electrical protection, like leather gloves or the sheathe on power cables.

Electricity is the flow of electrons. It is useful for powering a wide range of devices, but can also be dangerous if not handled carefully. Almost all metals are good conductors of electricity, while almost all non-metals, like rubber, cotton, and glass, are good insulators.


Circuits Overview

In this module, we will introduce what an electric circuit is and explain its purpose.We will also explain how electricity flows through a circuit, and see the difference between an open and a closed circuit. Skip to quiz!


Recall that electricity is defined as a flow of electrons that have been forced to move between atoms. The path that these electrons follow is called an electric circuit.mIt has to be a closed-loop, like a racecar circuit.

For the electrons to move and produce electricity, there needs to be a complete circuit. The most elemental circuits consist of a voltage source (battery), a load, and wires connecting them. A classic example is a battery, connected through wires, to a light bulb (load).

An electric circuit 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 electric current through the electric circuit, and blood vessels carry blood through the circulatory circuit.

The heart creates a pressure that pumps blood through the veins. A voltage source (battery) also creates a ‘pressure’ in an electric circuit. The electric ‘pressure’ that pushes electricity through a circuit is called voltage.

The heart creates pressure to deliver blood through the blood vessels to different organs.

Similarly, a battery provides voltage to drive a current through wires to different loads. This is what makes the light bulb glow.

Providing electric energy to loads using a source is the main objective of a circuit. Loads can be anything that requires electricity to work, like light bulbs, fans, clocks, stoves, etc.

Electrons travel from the negative terminal of the source, through the circuit, to the positive terminal. Recall that electrons are negatively charged, and are repelled by the negative terminal.

If the current’s path is broken, the circuit becomes an open circuit. In this 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 and not broken, the circuit becomes a closed circuit. In this 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

Recall that, for an electric current to exist, electrons have to be pushed in a specific direction through a circuit. The ability or potential to push electrons in a circuit is called voltage, represented by the letter ‘V’. Batteries are a voltage source, which is why they can create current in a circuit.

As an analogy, voltage can be compared to the height of a waterfall. The higher the waterfall is, the more force the water has when it hits the bottom. With a higher voltage, a bigger current can also be obtained.

Voltage is measured in ‘volts’, which are denoted by the letter ‘V’. For example, a 12 volt car battery is written as “12V”. With a higher voltage, a bigger current can also be obtained.

We refer to the rate at which the electrons flow through a conductor as current. Current is like how much water falls per second in the waterfall analogy. Current is typically identified as the letter ‘i’ in diagrams and formulas.

The unit of measurement for current is the ‘ampere’. The amperes, commonly shortened to amps, are denoted by the letter ‘A’.

Resistance is the opposition to the flow of electric current. It varies depending on the material and its shape. In the waterfall analogy, resistance is like rocks, trees, or other obstacles slowing down the flow of water.

Resistance is usually denoted by R’, and its unit of measurement is ‘ohm’, denoted by the omega symbol, ‘Ω’. Resistance can be measured with the use of an ohmmeter.

Voltage (v), current (i), and resistance (R) come together in a circuit to make it work. A voltage source connected to a circuit will cause a current to flow. This circuit will offer opposition to current flow, which are the resistances in the circuit.

All our electrical devices work as a circuit, and we operate them by opening and closing those circuits. To achieve this, we have switches included in the circuits. A switch physically opens or closes the circuit when activated.

A Simple Circuit

At a minimum, the following four elements are needed to create a simple circuit:

  1. Power source,

  2. Wires,

  3. Switch, and

  4. Load

A power source supplies electric power to the circuit. A battery is a great example of a voltage source. Wires provide an electric path for the current to flow that connects all elements in the circuit.

The switch is a device that opens or closes the circuit on-demand.The device in a circuit that consumes power is called load. Common examples are light bulbs, electric motors, electric heaters, etc.

The switch can be connected anywhere between the connected terminals. This is because the circuit can be opened and closed at any point in the loop.

For these components to work together, they have to be connected to form a circuit. Let’s see a step-by-step procedure on how to connect a light bulb to a battery and a switch.

Circuits are used to to provide a path for electric current. A simple circuit can be made up of an energy source, wires, and a load. A switch can be used to open and close a circuit for ease of operation.


Basic Circuit

In this module, we will go over more electrical components. We will also discuss the difference between alternating current (AC) and direct current (DC). Skip to quiz!


Recall that the flow of electricity in a circuit happens because electrons are pushed from the negative terminal of the source. This creates the electric current that travels through the circuit and all components connected in it. Circuits are how we power our devices!

Electrons travel from the negative terminal, through the circuit, and finally reach the positive terminal. Recall however that positive conventional current starts at the positive terminal and ends at the negative terminal.

An open circuit is one in which the circuit is broken and no current flows through it. A closed circuit forms a closed-loop for the current to flow. We use a switch to open and close circuits on-demand.

Think about a switch for a light bulb in our house. When we turn off the switch, it is an open circuit and the light bulb does not glow. When we turn on the switch, it is a closed circuit and the light bulb glows.

Additional Operating Principles

Recall that electrons are negatively charged and protons are positively charged. The valence electrons in atoms can become free electrons and move to other atoms. This movement of electrons will 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.

A positively or negatively charged item can discharge by contact. This is what happens when you get a shock from a metal object by touching it.

Electric charge is represented by the letter q, and is measured in units of Coulombs, which are written as a 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. This ability is present in every object, in a bigger or smaller capacity. Our bodies, balloons, plastic items, and styrofoam are common examples of items that have a capacity to hold charge.

This capacitance is represented by the letter C, and is measured in units of farads, which are written as an F’. Most items have a relatively small capacitance represented in microfarads (μF), which are one million times smaller than a farad. 1F = 1,000,000 μF

Another effect created by electricity is a magnetic field.This field is similar to those around magnets. Any time current (I) flows through a conductor it creates a directional magnetic field (B) around that conductor, as shown in the image.

Just like how current can create an electromagnetic field, magnetic fields can “induce”, or create, a voltage in any conductor that is exposed to them. This voltage then causes electrons to flow, producing electricity. When a magnetic field induces current flow, it is called inductance.

When we show inductance in a circuit, we show it by the letter ‘L’. When we measure the inductance, we use the unit ‘Henry’,which can be shortened to just the letter ‘H’.

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 is represented by the letter ‘P’, and is measured in units of Watts, which are written as W’.

Basic Components

So far, we have seen many important electrical characteristics. All these are useful in the creation of working electric circuits.

The basic electrical components used to create all electrical circuits can include some or all of the following:

  • Conductors,

  • Insulators,

  • Resistors,

  • Capacitors, and

  • Inductors

The most basic electrical circuit components are conductors and insulators. Recall that conductors are materials that allow for electrons to easily move through them. Most metals are very good electric conductors.

Insulators, on the other hand, are the opposite of conductors. These are materials that don’t easily allow for the flow of electrons. Rubber, glass, and ceramic are good insulators.

Resistors are electrical components designed with a specific amount of resistance. They are passive components, meaning they can only consume power. Resistors are commonly used to limit the current in a circuit.

If a light bulb is directly connected to a battery, the resulting current could damage the light bulb. This can be prevented by adding a resistor to the circuit. Adding a resistor to the circuit will reduce the amount of current flowing through the lightbulb.

The size in ohms of a resistor will determine how much current flows.If too small, the current can still be too high for the light bulb. If too big, the current might not be enough to power the light bulb.

Capacitors are electrical components designed to take advantage of the property of capacitance. Recall capacitance is the ability to hold electrical charge. We will see that capacitors can behave like short-term batteries.

Capacitors 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.

Recall that inductance is the tendency of a conductor to induce a voltage in the presence of a magnetic field. Electrical components that take advantage of this effect are called inductors.

Inductors store energy in a magnetic field. This energy 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), and

  • Direct current (DC)

The difference between these is how electrons flow in the circuit. It is very important to understand the differences and applications between AC and DC.

AC flows in both directions, while DC flows in only 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 cannot be stored.

Circuits can use many different components to achieve varied objectives. Conductors, insulators, resistors, capacitors, and inductors are the most common electronic components.

AC and DC have different purposes, but both are important.


Basic Formulas

This module will focus on the most important formulas for electric analysis: Ohm’s Law and Watt’s Law. Explanation on what the laws entail and examples will be provided. Skip to quiz!

Ohm’s Law

G. S. Ohm was a German physicist who discovered and published the law named after him. He discovered that electricity behaves like water in a pipe. Pressure increases, water flows faster. Voltages increases, current also increases.

Similarly, blockages in the pipe restrict water flow the same way that resistances reduce current flow. Ohm proposed that the current in a circuit is directly proportional to the voltage, and inversely proportional 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, the current is reduced or increased accordingly. This can be easily put into a formula as: V=I*R

The formula V=I*R can be also re-written as:



You can calculate any of these three values in a circuit, as long as you know the other two.

If you vary the resistance in a circuit that turns on a light, you can control how much current flows through it. By doing this, you can choose how bright the light glows. A resistor with a varying resistance is called a potentiometer.

Ohm’s Law: Calculations

This Sub-Topic will cover how to perform calculations with Ohm’s Law. We can calculate an unknown value in a circuit if the other values are known to us. We can do this by using Ohm's Triangle.

If the voltage source provides 120V, and the current circulating is 0.80A, what is the value of the resistance?




If the voltage source provides 240V, and the resistance has a value of 80Ω, what is the value of the resistance?




If I=5A and R=24Ω?




Watt’s Law

James Prescott Joule was an English mathematician, physicist, and brewer. He studied the nature of heat and its relationship with mechanical work. His work with steam engines led to his discoveries in electrical power.

Named in honor of the Scottish inventor, James Watt, electric power is measured in units of ‘Watts’, represented by the letter ‘W’. The power rating on a light bulb for example, is given in Watts.

Watt’s Law states that the power in an electrical circuit is the product of the voltage and the current. The formula for this law can be written as:


As with Ohm’s formula, by using simple algebra we can rewrite P=I*V as:



Again, any of these three values can be determined as long as you know the other two.

Watt’s Law: Calculations

Let’s use the Watt’s law to calculate the unknown variable in a basic circuit when knowing the other two variables. The slides in this Sub-Topic will use the same simple circuit, but changing the values of different parameters.

If the voltage source provides 240V, and the current circulating is 3.20 amps, what is the power being consumed?




If the voltage source provides 480V, and the power being consumed is 720W, how much current is circulating in the circuit?




Ohm’s Law and Watt’s Law are very useful tools in the world of electricity. Unknowns can easily be calculated when the other variables are known. In practice, we can use equipment to measure some key parameters, then we can calculate the rest.


Question #1: What is currently the biggest use of electricity in the residential sector?

  1. Office electronics

  2. Ovens

  3. HVAC systems

  4. Electric vehicle charging

Scroll down for the answer...

Answer:HVAC systems

HVAC systems are currently the biggest user of electricity in the residential sector.

Question #2: Electricity is caused by the flow of ______ .

  1. Atoms

  2. Water

  3. Wind

  4. Electrons

Scroll down for the answer...

Answer: Electrons

Electricity is caused by the flow of electrons.

Question #3: What kind of electrons are needed for the conduction of electricity?

  1. Valence electrons

  2. Outermost electrons

  3. Bohr’s Electrons

  4. Free Electrons

Scroll down for the answer...

Answer: Free Electrons

Free electrons are needed for the conduction of electricity.

Question #4: What does electricity cause in speakers to make sound?

  1. Vibration

  2. Rotation

  3. Heat

  4. Light

Scroll down for the answer...

Answer: Vibration

Electricity causes speakers to vibrate so that they make sound.

Question #5: Which of the following is a danger of electricity.

  1. Electrical shock

  2. Electrical burn

  3. Fire or explosions

  4. All of the above

Scroll down for the answer...

Answer: All of the above

All of these are dangers from electricity that can harm humans.

Question #6: A conductor is a material that _____.

  1. Makes sound

  2. Prevents electrons from flowing

  3. Allows electrons to flow easily

  4. Makes light

Scroll down for the answer...

Answer: Allows electrons to flow easily

A conductor is a material that allows electrons to flow easily.

Question #7: Which materials are generally the best conductors?

  1. Metals

  2. Non-Metals

  3. Plastics

  4. Ceramics

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Answer: Metals

Metals are generally the best conductors.

Question #8: Which of the following is an example of an insulator?

  1. Aluminum wire

  2. Metal armor

  3. Protective rubber gloves

  4. A silver fork

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Answer: Protective rubber gloves

Protective rubber gloves are an insulator.

Question #9: Which type of circuit has the ability to deliver electric power to a load?

  1. Circulatory circuit

  2. Open circuit

  3. Race car circuit

  4. Closed circuit

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Answer: Closed circuit

A closed circuit can deliver electric power from a source to a load, allowing electrons to travel from the negative to the positive terminals.

Question #10: Which unit denotes the amount of current circulating in a circuit?

  1. Volts (V)

  2. Ohms (Ω)

  3. Farads (F)

  4. Amperes (A)

Scroll down for the answer...

Answer: Amperes (A)

The ampere (A) is the unit used to measure the current in a circuit.

Question #11: Which element allows for a circuit to be easily opened or closed?

  1. Resistance

  2. Switch

  3. Load

  4. Source

Scroll down for the answer...

Answer: Switch

A switch permits a user to open or close a circuit when desired.

Question #12: Which of the following is NOT an essential part of a basic circuit?

  1. Power source

  2. Wires or other conductors

  3. Load or resistance

  4. Ohmmeter

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Answer: Ohmmeter

An ohmmeter is not an essential part of a basic circuit.

Question #13: What flows through an open circuit?

  1. Electrons

  2. Voltage

  3. Current

  4. Nothing

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Answer: Nothing

In an open circuit, nothing can flow since the loop is not closed.

Question #14: What are the units of measurement for capacitance?

  1. Coulombs, C

  2. Capacitance, C

  3. Farads, F

  4. Henrys, L

Scroll down for the answer...

Answer: Farads, F

Capacitance is measured in farads (F).

Question #15: Which attribute refers to the tendency of creating a voltage in a conductor that is inside a magnetic field?

  1. Capacitance

  2. Power

  3. Resistance

  4. Inductance

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Answer: Inductance

Inductance is the tendency of a conductor to create a voltage when inside a magnetic field.

Question #16: What represents the transfer of electrical energy over time, and how is it measured?

  1. Capacitance (Farads)

  2. Electric charge (Coulombs)

  3. Power (Watts)

  4. Inductance (Henrys)

Scroll down for the answer...

Answer: Power (Watts)

Electric power is the rate at which electrical energy is transferred, measured in Watts.

Question #17: Which electric components use an electric field to temporarily store energy?

  1. Capacitors

  2. Conductors

  3. Resistors

  4. Insulators

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Answer: Capacitors

Capacitors store energy in an electric field between the plates inside them.

Question #18: Which electric elements store energy in a magnetic field around them?

  1. Switches

  2. Inductors

  3. Load

  4. Source

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Answer: Inductors

Inductors store energy by creating a magnetic field around them when a current flows through them.

Question #19: Which type of current is preferred for long distance transmission?

  1. Direct Current (DC)

  2. Positive Current

  3. Alternating Current (AC)

  4. Negative Current

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Answer: Alternating Current (AC)

AC is usually preferred for long distance transmission, since DC loses much more power in this process.

Question #20: Which formula is related to Ohm’s law?

  1. V=I*R

  2. I=V÷R

  3. R=V÷I

  4. All of the above

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Answer: All of the above

All of the above. The formula that represents Ohm’s law can be rearranged to find any of the three variables.

Question #21: If you have a circuit powered by a 120V source, with a current of 2.5A, what is the size of the resistance in the circuit?

  1. 22Ω

  2. 48Ω

  3. 38Ω

  4. 52Ω

Scroll down for the answer...

Answer: 48Ω

The resistance is calculated as:




Question #22: If you have a circuit powered by a 120V source, and it has a 15Ω resistance, what will the current be?

  1. 6A

  2. 9A

  3. 8A

  4. 8V

Scroll down for the answer...

Answer: 8A

The current is calculated as:




Question #23: If you have a circuit with I=2.5A and a resistance of 192Ω, what is the voltage in the circuit?

  1. 480V

  2. 320V

  3. 120V

  4. 480A

Scroll down for the answer...

Answer: 480V

The voltage is calculated as:




Question #24: Which values are needed to find the power in a circuit?

  1. Voltage and length

  2. Current and voltage

  3. Current and number of switches

  4. Resistance and time

Scroll down for the answer...

Answer: Current and voltage

Current (I) and voltage (V) are needed to calculate power.

Question #25: If you have a circuit powered by a 5V source, with a circulating current of 0.5A, what is the power being consumed?

  1. 3.5W

  2. 10W

  3. 25W

  4. 2.5W

Scroll down for the answer...

Answer: 2.5W

The power is calculated as:




Question #26: If you have a circuit powered by a 12V source, and it is consuming 9.6W, what would the current in the circuit be?

  1. 0.8A

  2. 0.9A

  3. 0.6A

  4. 0.5A

Scroll down for the answer...

Answer: 0.8A

The current is calculated as:





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