Electric Circuits and Switches

The Journey Inside℠, an Intel® Education Program

Lesson 1: What Is Electricity?

When you turn on a light or pop some bread in the toaster, electricity is there and ready to work for you. But what exactly is it? To find out, you have to get really small. You have to go down to the atomic level.

Everything is made of atoms—you, your desk, your chair, your lunch, everything. These atoms contain electrons, which are particles with a tiny negative electric charge. In some materials, electrons can jump from atom to atom. But for the electrons to start jumping, there needs to be an imbalance of electrons and a path for the electrons to follow.

You’ve probably experienced electricity yourself. Ever touch a doorknob and get a shock? In this case, there was an imbalance of electrons between you and the doorknob. In an instant, this imbalance was corrected.

In a battery, for instance, a negative pole has a lot of electrons, and a positive pole has few. When you connect the two poles through the circuitry of a device like a flashlight, the electrons have a path they can use to flow from the negative to the positive pole to correct the imbalance. This is what we call an “electric current.” In this example, we get the electricity to do some work—lighting a bulb.

Lesson 2: Electricity in Your Home

Ever wonder why electricity is always there waiting in the wire for you to use? A good way to understand it is to compare household electricity to household plumbing. Turn a faucet handle and out pours the water. Why? Because there is:

  • A supply of water somewhere.
  • A pipe to carry the water.
  • A pressure difference between the water supply and your faucet.
  • A faucet to turn the water on and off.

Compare this to how you get electricity to a lamp. In this case, there is:

  • A power plant to supply moving electrons.
  • Wire to conduct the moving electrons.
  • More moving electrons at the power plant than in your lamp.
  • A switch to turn the current on and off.

Try the lesson: Electricity in your home.


Lesson 3: Big Circuits

We generally think of electric circuits as small things, like a lamp or an electric toothbrush. But what about the path electricity takes to get to your home? It’s a circuit too—a massive circuit!

Lesson 4: A Simple Circuit

We use lights all the time, but have you ever wondered how they work? Let’s take a look at a flashlight. It uses a simple circuit, which is made up of four parts: a power source, conducting path, switch, and (electrical) load.

  • The power source is what pushes the electricity through the circuit.
  • The conducting path is what connects all the parts of the circuit. It makes the pathway that the electricity travels through.
  • The switch is the part of the circuit that can break or make the flow of electricity. We use the switch to turn the power on or off.
  • The electricity in the circuit powers the load.

Try the lesson: A simple circuit: The flashlight.


Lesson 5: Build a Light Bulb Circuit

The best way to understand electric circuits is to build them, and it can be a lot of fun too. Think about the parts of a simple circuit that you explored in Lesson 4. Use what you know to build a light bulb circuit. If you’ve done it correctly, the bulb will light up.

Find the power source and drag it into the circuit. Remember that the power source pushes the electricity through the circuit.

Now, create a conducting path. Your conducting path should connect all the parts of the circuit and create a pathway for the electricity to travel through. Finally, drag the load to complete the circuit.

After you build the light bulb circuit, click the bulb to reverse the wires. Now the electricity is flowing in the opposite direction!

Try the lesson: Build a light bulb circuit.


Lesson 6: Will It, or Won’t It? (Solids)

Electrons move freely when we turn on a circuit. However, there are certain types of materials that allow or don’t allow those electrons to transfer. These are conductors and insulators.

An insulator is a material that does not transfer electricity. It has an important job: to block electricity from going to places where it shouldn’t go. Think of insulators as security guards outside of a big fancy house—nothing gets past them.

A conductor is a material that is able to transfer an electric current. It’s the opposite of an insulator. If the insulators are security guards, the conductors are the people opening the front door of the house saying, “Come on in! The party’s here!”

Try the lesson: Will it, or won’t it? (Solids).


Lesson 7: Resistance

Resistance is a physical property of materials. If a material has a high resistance, it opposes the passage of a steady electric current. The lower the resistance, the easier it is to force electrons to leave atoms and move through the material. Metals, by nature, have low resistance. That’s why metals like copper are used as electrical conductors. Rubber, wood, and plastics, on the other hand, have a high resistance. That means it’s nearly impossible to force their electrons to leave their atoms. A plastic coating around wire acts as an insulator, preventing the flow of electricity.

Lesson 8: Will It, or Won’t It? (Liquids)

Remember, an insulator is a material that does not transfer electricity and a conductor is a material that is able to transfer electricity.

For liquids, an electrolyte is a liquid that can conduct electricity.

Examples of strong electrolytes include salt water; hydrochloric acid solution, which is often used in batteries; and silver nitrite solution, which can help stop bleeding on a small cut.

Weak electrolytes don’t conduct electricity very well. Examples of weak electrolytes are lemon juice, rainwater, and carbonic acid, which is commonly found in carbonated beverages like soda.

Try the activity: Will it, or won’t it? (Liquids).


Lesson 9: Mechanical Switches

As convenient as it is to be able to turn on electricity, think how bad it would be if you couldn’t turn it off. An electric burner on a stove that you couldn’t turn off could be a real fire hazard. Switches that allow you to turn on and off lights or a toaster oven are called mechanical switches. They’re “mechanical” because they have moving parts.

Try the activity: Experimenting with mechanical switches.


Lesson 10: Nonmechanical Switches – Transistors

As you will learn in the Digital Information lessons, computers contain billions of transistors, which are microscopic electronic switches that turn on and off billions of times a second. Computers and other electronic devices transform communications—words, images, sounds, videos, etc.—into a simple code that uses the numerals 0 and 1 to represent the off and on states of a transistor.

Mechanical switches are too slow to handle the constant switching between on and off. That’s why computers use nonmechanical switches powered by electricity in order to work. This requires a semiconductor, which is a naturally poor conductor that can be easily changed to conduct electricity in certain situations.

The best material for a computer’s semiconductor is silicon, a nonmetallic element.

You can see in the diagram that two terminals—the source (where current goes in) and the drain (where current goes out)—are negatively charged. They’re made of n-type silicon (n for negative). Both terminals sit on a positively charged well of silicon connected to the gate terminal. The well silicon is called p-type silicon (p for positive). When a charge is applied to the gate terminal, electrons in the p-type silicon are drawn to the space between the source and drain terminals and form an electron channel. Electrons now flow from the source to the drain. In this position, the transistor is on. Remove the charge from the gate terminal and the transistor returns to its off state.

Try the activity: Experimenting with nonmechanical switches.