Electricity, Magnetism and Electromagnetism

Electricity, magnetism and electromagnetism

Electricity and magnetism are two of the most useful ideas in all of physics, and they turn out to be deeply linked. Electricity is about the flow of tiny charges around a circuit, driven by a push from a battery or the mains, and slowed by resistance. Magnetism is about the invisible force around a magnet, felt most strongly at its poles. Put the two together and you get electromagnetism: pass a current through a coil of wire and it behaves like a magnet, an idea that powers motors, generators, loudspeakers and much more. This module covers circuits and the sums that go with them, the behaviour of magnets and their fields, and how electricity and magnetism work together in everyday machines.

Words for electricity and magnetism

Learn these terms before the units are matched up. They name the ideas used in electricity and magnetism.

Match each electrical quantity to its unit

Series against parallel circuits

Components can be wired in two main ways, and they behave differently. Knowing which is which explains a lot about how circuits work.

Which quantity has increased?

Two identical bulbs are added in series to a circuit and the current gets smaller. What has increased?

• The total resistance
• The voltage of the battery
• The charge stored in the battery
• The magnetism in the wire

Magnets and magnetic fields

Every magnet has two poles, a north and a south, and the rule is simple: like poles push apart, unlike poles pull together. Around a magnet is a region called a magnetic field, where the force can be felt, and it is strongest at the poles. We picture this field with lines that run from the north pole round to the south pole, drawn closer together where the field is stronger. Only a few materials, chiefly iron, steel, nickel and cobalt, are magnetic; most everyday things, such as wood, plastic and copper, are not. Knowing the poles and the field is the key to explaining how compasses, motors and generators all work.

Pick the true electricity facts

Select every statement about electricity that is true.

• Current is the flow of electric charge
• Voltage is the push that drives the current
• Resistance opposes the flow of current
• Electricity flows with no source at all
• Charge flows easily through wood

Order how to build an electromagnet

Put the steps of making a simple electromagnet into a sensible order.

• Take a length of insulated wire
• Wind it into a coil around an iron nail
• Connect the ends to a battery
• Switch on so a current flows
• The nail becomes magnetic and lifts paperclips

Complete the electricity facts

The flow of electric charge around a circuit is called _____. The push that drives that flow is the _____, measured in volts. Anything that opposes the flow is called _____, measured in ohms. A coil of wire that becomes magnetic only when a current flows is an _____.

Tap the two magnetic materials

Read these four everyday materials. Tap the TWO that are magnetic.

• an iron nail
• a steel paperclip
• a wooden ruler
• a plastic cup

Water flowing in pipes

Electricity in a circuit is easier to picture as water in pipes. The moving water is like the flow of charge: lots of water rushing past is a big flow, a trickle is a small one. The pump that pushes the water round is like the driving push from a battery: a stronger pump sends the water round faster. And a narrow, clogged pipe is like something that holds the flow back: the tighter the squeeze, the less gets through for the same push. Once you see the pump, the pipes and the squeeze, the whole circuit starts to make sense, and you can often predict what a change will do before you even build it.

Work out the voltage

A current of two amperes flows through a resistor of six ohms. Using the idea that voltage is current times resistance, what is the voltage across it in volts? Give the number only.

Apply your electricity knowledge

Read each situation and choose the best answer.

• You want the other bulbs to stay lit if one bulb fails. How should you wire them?
• You want to make an electromagnet stronger. What helps?
• A wooden spoon will not stick to a magnet. Why?

Build an electricity point

Choose the word for each gap to complete one point about circuits.

Explain electricity and magnetism

A friend finds electricity and magnetism confusing. Using what you have learned, explain the main ideas clearly.

• Explain what current, voltage and resistance mean
• Explain the difference between a series and a parallel circuit
• Explain what a magnet and a magnetic field are
• Explain what an electromagnet is and one way to make it stronger
• Explain how voltage, current and resistance are linked