Insulators and Conductors: Examples, Definitions & Qualities

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  • 0:05 Conductors and Insulators
  • 2:56 Conductivity
  • 4:24 Conductors and…
  • 5:35 Lesson Summary
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Lesson Transcript
Instructor
Jim Heald

Jim has taught undergraduate engineering courses and has a master's degree in mechanical engineering.

Expert Contributor
Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

In this lesson, we'll explore the reasons that some materials conduct electrical energy with ease while others block it almost completely. We'll also talk about the property of conductivity and some everyday examples of insulators and conductors.

Conductors and Insulators

Back in the old days, if someone's house caught on fire, volunteers would rush to the scene and form a bucket brigade to put out the flames. If you think about it, you could say that the bucket brigade was 'conducting' water from the source to the fire. But, what if the volunteers stopped passing the water?

Well, we know one thing: the house would burn to the ground because it was effectively 'insulated' from the water! The bucket brigade scenario is actually very similar to why some materials act like electrical conductors and others act like electrical insulators. But, to find the actors in our electrical 'bucket brigade', we have to start at the atomic level.

Not all atoms are created equal. Some atoms don't hold on to their outer electrons very tightly. These are known as free electrons because they are literally free to roam around from atom to atom. Free electrons are the members of our electrical bucket brigade passing electrical energy from one electron to another.

Free electrons are free to roam from atom to atom.
Free Electrons

A material with many free electrons allows easy transfer of electrical energy and is therefore called a conductor. If we send an energetic electron into a conductor, it will impact a free electron, knocking it down the line until it hits another free electron. This sets up a chain reaction of impacts that conducts the electrical energy through the material.

A good way to think of it is like a group of balls spread out on a billiards table. Our energetic electron is like the cue ball being shot into the group and impacting one ball, which in turn knocks into another ball and so on down the line. Before you know it, the energy from the cue ball has been 'conducted' all the way to the other end of the table. The only real difference between billiard balls and electrons is that electrons conduct electrical energy at nearly the speed of light!

Insulators have very few free electrons and do not transfer electrical energy well.
Insulator

On the other end of the spectrum, there are atoms that hold on to their electrons very tightly. A material that contains these types of atoms has very few, if any, free electrons and does not transfer electrical energy well, if at all. This type of material is called an insulator.

If we send an energetic electron into an insulator, it effectively bounces off the atoms, unable to transfer its energy to the tightly bound electrons. It will keep bouncing around until it either frees another electron or until it simply runs out of energy!

Going back to our billiard table analogy, this is very similar to the cue ball simply bouncing off the sides of the table. Either it will hit another ball and transfer its energy, or it will just stop rolling because of friction.

Conductivity

The ability of a material to conduct electrical energy is known as its conductivity. Not surprisingly, materials that are good conductors have high conductivity, while materials that are good insulators have low conductivity. The conductivity of a material is dependent on the number of free electrons available, and this varies greatly between the different types of atoms. In general, the materials with the highest conductivities, or best conductors, are metals - but this doesn't mean that other materials aren't capable of conducting electricity. If that were true, no one would ever be in danger of getting electrocuted!

Examples of materials with low conductivities
Low Conductivity

On the other end of the spectrum, the materials with the lowest conductivities, or best insulators, are glass, ceramic, rubber and some plastics. Not all materials are classified as insulators or conductors, because in the real world, they don't do a particularly good job of either one.

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Additional Activities

Testing Insulators and Conductors

In this experiment, students will be setting up a small circuit and incorporating different materials to test for conductivity. To complete this experiment you'll need one 9V battery and a holder, a small light bulb and a holder, and three pieces of insulated wire. You'll also need different materials to test as conductors or insulators, such as paperclips, wood, plastic or other types of metal. Try testing different objects you find around you, making sure you test objects made of different types of materials.

Student Instructions

In this experiment, you will be creating a circuit to test for the conductive properties of different materials. The circuit will be made of a battery, a light bulb, wires, and the materials you are testing. If the circuit is complete, meaning electrons can pass through the material, the light bulb can light up and you'll know the material was a conductor. Follow the steps below to set up your circuit and test the materials. You should use paperclips, copper wire, and a pencil to start, then choose two additional materials to test.

  1. Start by connecting one side of the battery to the light bulb with an insulated copper wire.
  2. Next, add another wire to the other side of the battery, but don't connect it to anything yet.
  3. Add another wire to the other side of the lightbulb but also don't connect it to anything yet.
  4. Use the two free ends of the wires and connect them to the materials you are testing to complete the circuit. Record your results in the table below if the material allows the light bulb to light.

MaterialResults (light bulb on or off?
Paperclips
Copper wire
Pencil


Questions

  1. Which materials were conductors and which were insulators and how did you know?
  2. Which materials were the best conductors and why?
  3. Why is it important to understand the uses of conductors and insulators?

Expected Results

Students should see that metals are good conductors and are able to complete the circuit, allowing the light bulb to light because they have free electrons in metallic bonds that are able to travel freely. If this does not happen, test the light bulb with the battery alone in the circuit and make sure that it lights. You may need a new battery, a new light bulb or both. Wood and plastic will act as insulators and not complete the circuit.

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