C. Matter and Energy · Electrical Phenomena, Energy, and Devices

Conductors and Insulators

C2.3 A1.2 A1.4 A1.5About 45 minutes

Learning goals

I can explain what conductors and insulators are.
I can build a safe tester and use it to sort materials into conductors and insulators.
I can identify good conductors (like metals) and good insulators (like plastic, rubber, glass and wood).
I can explain how conductors and insulators keep us safe around electricity.

Words to know

conductor
A material that lets electric current flow through it easily. Most metals are good conductors.

insulator
A material that does not let electric current flow through it easily, such as plastic, rubber, glass or dry wood.

graphite
The grey material in a pencil ("pencil lead"). It conducts electricity, but not as well as metal.

prediction
What you think will happen, and why, before you test it.

Why are wires covered in plastic?

Look at the cord on a lamp or a phone charger. If a grown-up cut one open (don't try this!), you would see shiny copper metal inside, wrapped in plastic or rubber outside.

Why two materials? Because they do two opposite jobs. The copper lets electricity flow. The plastic stops it from getting out and reaching your hand. In this lesson you will find out which materials let current flow and which ones block it.

The cut end of a white electrical cord, showing many shiny copper wire strands inside the plastic coating. — The copper inside is a conductor that carries the current. The white plastic outside is an insulator that keeps the current from reaching you. AI-generated image

Inside a cord, copper (a conductor) carries the current. The plastic covering (an insulator) keeps the current inside the wire and away from you.

Conductors and insulators

Conductors let electric current flow through them easily. In conductors, electrons can move freely from atom to atom.

Good conductors: metals such as copper, aluminum, steel (paper clips, nails, keys), silver and gold.
Graphite (pencil "lead") conducts too, but not as well as metal.
Water with things dissolved in it, like tap water and salt water, conducts electricity. So does the human body, which is mostly water. This is why water and electricity are a dangerous mix.

Insulators do not let current flow through them easily. Their electrons are held tightly and can't move along.

Good insulators: plastic, rubber, glass, dry wood, paper, cloth, ceramic (like a mug) and air.

Remember from Lesson 1: static charge builds up best on insulators, like a rubber balloon, because the charge can't flow away. On a conductor, charge escapes easily.

A conductivity tester. The circuit has a gap. If the test object is a conductor, it closes the gap, current flows and the bulb lights. If it is an insulator, the gap stays open and the bulb stays off.

Where you see it	Conductor (lets current through)	Insulator (keeps us safe)
Electrical cord	Copper wires inside	Plastic or rubber covering
Plug	Metal prongs	Plastic body you hold
Electrician's screwdriver	Metal tip	Plastic or rubber handle
Power line on a pole	Aluminum or copper wire	Glass, ceramic or plastic insulators that hold the wire to the pole
Powerline technician	(stays away from touching live wires)	Rubber gloves, sleeves and other insulated gear

Conductors and insulators work together to make electricity both useful and safe.

Worked example

Let's predict and explain a test

Noor tests four objects with her tester: a steel spoon, a plastic ruler, a pencil lead, and a glass marble. Predict the result for each and explain.

Steel spoon: steel is a metal, a good conductor. Prediction: the bulb lights.
Plastic ruler: plastic is an insulator. Prediction: the bulb stays off.
Pencil lead (graphite): graphite conducts, but not as well as metal. Prediction: the bulb may glow dimly, or not at all with a weak battery.
Glass marble: glass is an insulator. Prediction: the bulb stays off.

Conductors: steel spoon (bright), pencil lead (dim or maybe not visible). Insulators: plastic ruler, glass marble.

Just for fun

What did the copper wire say to its plastic covering?

"Thanks, you've got me covered!"

Hands-on activity

Build a conductivity tester

You need: 2 AA batteries, a small flashlight bulb (take one from an old flashlight that used 2 AA batteries, or buy one at a hardware store), aluminum foil, masking or electrical tape, and test objects such as: a paper clip, a coin, a key, a metal spoon, a plastic spoon, an eraser, a rubber band, a wooden craft stick, a pencil sharpened at both ends, a piece of paper, a cloth, a glass jar and a piece of aluminum foil.

Make the wires

Tear off three strips of foil, each about 30 cm long and 5 cm wide. Fold each one lengthwise several times to make a thin, flat "wire".
Wrap tape around each foil wire, leaving about 2 cm of bare foil at each end. The tape is an insulator, like the plastic on a real wire.

Build the tester

Tape the two batteries together end to end, the + end of one touching the − end of the other, so they push in the same direction.
Wire 1: tape one end to the + end of the battery pair. Wrap the other end around the metal side of the bulb's base. It must not touch the tip at the bottom of the bulb.
Wire 2: tape one end to the tip at the bottom of the bulb. Leave the other end free. This is test lead A.
Wire 3: tape one end to the − end of the battery pair. Leave the other end free. This is test lead B.
Touch leads A and B together. The bulb should light. If it doesn't, check every connection.

Test (A1.2)

Make a table: Object, Material, Prediction, Result (lights / dim / off), Conductor or insulator?
Predict first. Then press both leads onto the object at the same time, a few centimetres apart.
For the pencil, touch the leads to the grey graphite at each sharpened end.

Share it (A1.5): write a conclusion: "The conductors I found were... They were all... (made of what?). The insulators were..."

What to look for: all the metal objects light the bulb. The pencil lead may glow dimly. Plastic, rubber, wood, paper, cloth and glass leave it off. Coins conduct because they are made of metal.

Safety (A1.4):

Don't short-circuit the batteries. Never connect the battery's + and − ends directly with foil or metal without the bulb in the path. With no bulb in the way, a big current flows, and the foil and battery get hot quickly. If it happens, pull the foil off right away and let things cool. Disconnect the tester when you are finished.
Use only AA batteries, never a wall outlet. Don't test anything that plugs in.
Ask a grown-up to help if a light bulb breaks.

Electrical safety outdoors and at home

Never touch electrical devices, plugs or switches with wet hands, and keep electrical devices away from bathtubs and sinks. Water and your body both conduct.
Stay at least 10 metres (about the length of a school bus) away from a fallen power line, and tell an adult to call 911 and the local electricity company.
Fly kites and climb trees far away from power lines.
In Ontario, people often call electricity "hydro". If a power line is down, it's a "hydro" emergency.

Your turn

What is a conductor?

What is an insulator?

Name three good conductors.

Name three good insulators.

Why is the inside of an electrical cord made of copper?

Why is the outside of an electrical cord covered with plastic?

You touch the tester leads to a key and the bulb lights. Is the key a conductor or an insulator?

More practice: warm-up

Conductor or insulator? An aluminum pie plate.

Conductor or insulator? A rubber boot.

Conductor or insulator? A steel nail.

Conductor or insulator? A wooden spoon.

Conductor or insulator? A glass window.

More practice: on your own

Why should you never use a hair dryer while sitting in the bathtub?

Why do electricians use screwdrivers with plastic or rubber handles?

Kai's tester lit the bulb dimly when he tested pencil lead, but brightly for a paper clip. What does this tell you?

Why are power lines held to their poles by glass or ceramic pieces instead of metal?

Why does a balloon hold static charge better than a metal spoon?

Challenge

A plastic pen has a metal clip. Predict what the tester will show if you touch both leads to the metal clip, and what it will show if you touch one lead to the clip and one to the plastic part. Explain.

Design a safe tool for changing a light bulb in a high ceiling light (with the power switched off). Which parts would you make from conductors and which from insulators? Explain.

Leila tested 6 objects. Results: copper wire (bright), plastic straw (off), coin (bright), cork (off), aluminum can with paint on the outside (off when touching the paint, bright when touching the shiny metal rim), wool (off). Write a conclusion.

Check your understanding

Quiz

Which material is the best conductor?

Which material is an insulator?

When you test a coin with a conductivity tester, the bulb lights. This shows the coin...

Why are the handles of an electrician's pliers covered in rubber?

Why is it dangerous to touch a light switch with wet hands?

How far should you stay from a fallen power line?

For parents and teachers

Big idea (C2.3): identify materials that are good conductors (metals, graphite, water with dissolved substances) and good insulators (plastic, rubber, glass, dry wood, paper, cloth, air). Building and using the tester practises scientific experimentation (predict, test, record, conclude: A1.2), safety (A1.4) and communication (A1.5).

How to help: help your child build the tester; the most common fault is wire 1 touching both the side and the tip of the bulb, or loose connections at the battery. Use a bulb from an old two-AA flashlight so it is the right size for 3 V. Keep the experiment to AA batteries.

Common difficulties:

Thinking all shiny things conduct, or all metal-looking things do. Painted or plastic-coated metal may not light the bulb where the coating is.
Thinking water is an insulator. Tap water and salt water conduct, and that's why water and electricity are dangerous together, even though a small battery tester may not light a bulb through water.
Not linking insulators to safety. Point out the plastic on cords, the rubber on tool handles and insulators on hydro poles.

Safety: warn your child not to connect the battery's two ends with foil without the bulb in the path (a short circuit): the foil and batteries get hot quickly. Disconnect the tester when finished. Teach the 10-metre rule for downed power lines.