Two amazing forces
Electricity lights our homes, and magnets stick notes to the fridge. These two forces are closely linked. Moving electricity can make magnetism, and moving magnets can make electricity.
Static electricity
Everything is made of tiny particles with electric charges. Usually, the positive and negative charges balance out. But rubbing some materials together can move negative charges (electrons) from one object to another. This build-up is static electricity.
- Rub a balloon on your hair, and your hair stands up.
- Walk across carpet in socks, then touch a doorknob. Zap!
- Lightning is a giant spark of static electricity.
Rule: like charges repel; opposite charges attract.
Current electricity
Current electricity is a steady flow of electric charge through a wire. It powers lights, toys and computers.
Circuits
Electricity flows only if there’s a complete path called a circuit. A simple circuit has:
| Part | Job |
|---|---|
| Energy source (battery) | Pushes the charge |
| Wires | Carry the charge |
| Load (bulb, buzzer, motor) | Uses the energy |
| Switch | Opens or closes the circuit |
- Closed circuit: the path is complete; electricity flows; the bulb lights.
- Open circuit: there’s a gap; electricity stops; the bulb is off.
A switch works by opening and closing a gap.
Series and parallel circuits
| Series circuit | Parallel circuit | |
|---|---|---|
| Paths | One path | Two or more paths |
| If one bulb burns out | All go out | Others stay on |
| Bulb brightness (adding bulbs) | Dimmer | Stays bright |
| Used in | Some old holiday lights | Homes |
Conductors and insulators
| Conductors (let electricity flow) | Insulators (block electricity) |
|---|---|
| Copper, aluminum, iron | Plastic, rubber, glass |
| Water (with impurities) | Wood (dry), cloth |
| Graphite (pencil lead) | Air |
Wires are made of copper (a conductor) covered in plastic (an insulator) to keep us safe.
Electrical safety
- Never put anything except a plug into an outlet.
- Keep electrical devices away from water.
- Don’t pull a plug out by its cord.
- Stay far away from fallen power lines.
- During lightning storms, go indoors.
Magnets
A magnet attracts objects made of iron, nickel and cobalt.
- Every magnet has a north pole and a south pole.
- Opposite poles attract (N and S).
- Like poles repel (N and N, or S and S).
- The area around a magnet where its force acts is its magnetic field.
Earth is a giant magnet. A compass needle is a tiny magnet that lines up with Earth’s magnetic field and points north.
Electricity and magnetism together
In 1820, Hans Christian Ørsted noticed that a wire carrying current made a compass needle move. Electricity can make magnetism!
Electromagnets
An electromagnet is made by wrapping wire around an iron nail and connecting it to a battery. When current flows, the nail becomes a magnet. When the current stops, the magnetism goes away.
Make it stronger by:
- adding more coils of wire
- using a stronger battery
- using an iron core
Electromagnets are used in junkyard cranes, doorbells, speakers, MRI machines and electric motors.
Generators
Moving a magnet near a coil of wire makes electricity. This is how power plants and wind turbines make electricity.
Common mistakes
- Thinking all metals are magnetic. Aluminum and copper aren’t.
- Thinking a battery stores electricity. It stores chemical energy that becomes electrical energy.
- Thinking electricity is used up in a bulb. The charges flow back to the battery; their energy is used.
Try it yourself
- Build a circuit with a battery, wires and a bulb. Add a paper clip switch.
- Test objects (coin, eraser, spoon, foil, pencil lead) in your circuit. Which are conductors?
- Wrap wire 20 times around a nail and connect it to a battery. Count how many paper clips it picks up. Try 40 wraps.
Quick recap
- Static electricity is built-up charge; current electricity is flowing charge.
- A circuit must be closed for electricity to flow.
- Conductors let electricity through; insulators don’t.
- Magnets have north and south poles; opposites attract.
- Electricity can make magnetism (electromagnets), and magnetism can make electricity (generators).