What does it mean if something conducts electricity?
What is the difference between an electrical conductor and insulator?
Why are insulators important?
We use electric wires in electric circuits. Did you have a close look at the wire? Did you notice what materials are used on the inside and outside of the wire? We should also know why two different materials make up an electric wire.
What are conductors and insulators?
We can say that a material or object conducts electricity or it does not. But what does this mean? Let's do an investigation to find out. To do this we are going to use a simple circuit. We will connect pieces of different materials into a closed circuit with a light bulb in it. We can easily see if the material is a conductor.
How will you know if the material in the simple circuit conducts electricity?
The bulb will light up.
What kind of materials can we use in electric circuits?
One cannot investigate materials with low but significant conductance such as salt water. Later there is reference to shocking and the dangers involved. The reason we get shocked is because we are pretty good conductors. This is mostly due to the fact that our bodies have a fair amount of salt in solution. Also, pure water is a very poor conductor and poses much less of a shock risk. In this investigation, some substances, such as salt water, cannot be tested (unless many batteries are connected in series to the test circuit).
AIM:
Write down an aim for this investigation.
To investigate if materials have conducting or insulating properties
MATERIALS AND APPARATUS:
D-size battery (1.5 V)
torch light bulb
three pieces of electric wire 15-20 cm long with the ends (about 1 cm) stripped of the plastic insulating material
adhesive tape or Prestik
various objects made of different materials like:
metal paper clip (remove the plastic if covered)
paper clip covered with plastic
rubber band
nail
glass object (rod, tube or just a piece of glass)
pen
coins (brass and silver)
cardboard
paper (fold the paper to form at least 4 layers to make it easier to connect in a circuit)
steel wool
piece of wood
pencil (contact points on the wood)
pencil with both sides sharpened to expose the lead, test the lead part of the pencil
rubber
chalk
piece of ceramic
aluminium foil
metal spoon
plastic spoon
piece of leather
drinking straw
styrofoam
Learners can work in pairs, or groups of 3-4. The idea is to investigate different types of materials first to see if they conduct electricity or not so that learners come to the conclusion themselves that conductors are normally metals, and insulators (non-conductors) are normally non-metals.
METHOD:
Use three electrical wires to set up the electric circuit as shown below. Note that the ends of two of the wires are not touching. What do we call such a circuit?
open circuit
Draw the circuit diagram for the circuit shown in the sketch in the space on the right of the sketch.
Sketch
Circuit diagram
Test that the circuit is connected properly by touching A and B to each other and making sure that the bulb lights up/
Take the first one of the objects in the list above. Put the object between the two wire ends at A and B.
The sketch below shows how to do it. Make sure there is good contact between the object and the wire ends.
Make sure learners only touch the ends of the wire to the object and do not touch the object themselves with their hands while they are completing the circuit, to prevent breaking the electric circuit.
Test each object as shown here with the nail.
Does the bulb light up or not? Write the name of the object in the left or right column of the table below, depending if the bulb lights up or not.
Repeat for all the other objects in the list.
Some objects are composites of conductors and insulators. The visually different parts should be tested as well. For example, a knife may have a plastic handle, so test the handle as well as the metal blade.
RESULTS AND OBSERVATIONS:
Record your results below
Bulb lights up
Bulb does not light up
What do the objects that lit up the bulb have in common?
All the objects that lit up the bulb are made of metallic materials. The lead core of a pencil (graphite) also conducts electricity. Some metals are better conductors than others.
What do all the objects that did not light up the bulb have in common?
They were all made from non-metals, such as plastic, wood, glass, ceramics, etc
Some metals are better conductors than others. If the bulb does not light up with some metallic objects, it might be that the current is very small. Try an LED in this case to show that there is a current. Be careful! Remember that an LED only conducts in one direction. It should be connected correctly in the circuit: positive terminal of the LED connected to the positive terminal of the battery.
CONCLUSION:
Write a conclusion for this investigation below.
Metals conduct electricity and non-metals do not conduct.
If the circuit is closed, the bulb lights up. We have learnt before that in such a case there is an electric current in the circuit. A material that allows a path for an electric current is called an electrical conductor. The material conducts electricity.
What type of materials did not light up the bulb?
mostly non-metallic materials
Although the circuit seems closed, the bulb did not light up. What does that mean?
There is not an electric current in the circuit.
In this case the path for the electric current is broken. We call a material that does not allow a path for an electric current an insulator.
Good electrical conductors and insulators
A good electrical conductor is a material or substance that allows an electrical current to pass through it easily. We call the ability to conduct conductivity. Electrical conductors are usually metal because metals generally have high conductivity. Copper is one of the best electrical conductors and this is why it is the most common material used for electrical wiring. Gold and silver are even better conductors than copper, but they are very expensive and only used sometimes.
Insulators are non-conducting materials that do not easily allow current to pass through them. This does not mean that current can not pass through them at all. For example, we generally consider air an insulator, however, lightning can cause electric current to pass through air. Similarly, rubber gloves and shoes will protect you from mains electric current, but not from lightning. Examples of insulators are plastic, rubber, and wood.
When two conducting materials make contact, electricity can pass through them. Our bodies are also good conductors of electricity. This means electric current can easily flow through you and into the Earth, giving you a shock. That is why we cover conducting wire with insulating materials (like the plastic around extension cords). We want to protect ourselves from being shocked, and prevent the electrical current from passing to other conductors.
The importance of electrical insulators
Think of the electric wires that you use in class for the activities. Why do you think they are covered in plastic? The plastic is an insulator and therefore prevents you from getting a shock. The plastic coating acts as a barrier that prevents you from getting a shock, allowing you to handle the wire when the circuit is on.
Electrical insulators are also used in other places. Have you ever looked up at power lines or telephone lines? You will see that the poles that carry the lines are sometimes made of wood. Wood does not conduct electricity so the electric current can therefore not get from the wires into the pole.
Sometimes you will also see little white or coloured caps holding the wires as in the photo below. These caps are made of ceramic which also does not conduct electricity.
In this photo, the wooden poles and white ceramic caps are electrical insulators.
Sometimes, it is especially important to have ceramic electrical insulators between two different metal conductors to prevent electric current from flowing between the different parts such as in the photo below.
Can you see the dark red-brown ceramic electrical insulators?
You can also point out the electric rings in the photo which are also electrical insulators and a further precaution.
Do you remember naming the different parts in a bulb? Look at the picture of a bulb again below and explain why you think the piece separating the electric metal pins (conductors) is made of glass.
The glass is an insulator and therefore prevents electric current from flowing through the bottom of the electric pins and not through the coil at the top. With the glass insulation, the electric current rather flows through the coil at the top which then heats up and produces light.
Electricians are people whose job it is to work with electricity and fix the wiring in houses and other buildings. Electricians often wear rubber gloves to protect themselves from getting a shock. Rubber is an electrical insulator.
Some materials allow electric current in them. They are called conductors.
Some materials do not allow electric current in them. They are called insulators.
Metals are usually conductors and non-metals are usually insulators.
Electrical insulators have important functions like insulating wires or protection from electrical shock, e.g. an electrician's rubber gloves.
Suppose you have found a piece of material. You are not sure what the material is. You want to find out if it is a good conductor or a good insulator. Describe in words what you would do to determine if the material is an electrical conductor.
Set up an electric circuit as was done in the investigation with a battery, a bulb, and electric wires. Two ends of the wire must be unconnected so it is an open circuit. Test the object/material by placing it between the two ends of the wires to complete the circuit. If the material is an electrical conductor then the bulb will light up.
What is the difference between an electrical conductor and insulator?
An electrical conductor allows electric current to flow through it (it will complete an electric circuit) and an electrical insulator does not allow electric current to flow through it (it will not complete an electric circuit).
What kinds of materials are used to make electric wires? What are the functions of the materials?
A metal such as copper is used to make the inside of the wire as copper conducts electricity. The copper wire is covered in a material such as plastic which is an insulator to protect people handling the wire and also prevent the wire from making an electrical connection with other metal objects.
Why are insulators important?
Insulators protect people from electric shock; in some cases from possible death. Insulators also protect appliances from damage.
The pole is made of wood which does not conduct electricity and there are ceramic caps between the power lines and the pole which act as further insulators.
The man in the following picture is setting up an electric generator. Why is the man wearing gloves while he does this? Why is he also wearing boots with thick rubber soles?
This man is wearing gloves. http://www.flickr.com/photos/editor/72550973/sizes/l/
He is wearing gloves made of material and rubber as they are electrical insulators and therefore protect him from getting an electric shock when handling electrical wires and appliances. The thick soles on his shoes also prevent an electric current from passing through him and into the Earth.
