Physics P2: Waves, Electricity, Magnetism and Space

The physics of waves, circuits and space

Part two of the physics course looks at four connected ideas. Waves carry energy from place to place without carrying matter along with them, and light is one member of a whole family of waves called the electromagnetic spectrum. Electricity is the flow of charge around a circuit, and by joining parts in different ways we can control what that flow does. Magnetism and electricity turn out to be two sides of the same thing: a current can make a magnet, and a magnet can help make a current. Finally, space physics uses the light from distant galaxies to work out that the whole universe is spreading apart. This module covers each of these in turn, describing every relationship in words rather than symbols, the way a written answer should read.

Words for waves, electricity and space

Learn these terms before the P2 ideas are matched up. They name the ideas used in this topic.

Match each P2 idea to what it means

Series against parallel circuits

Parts of a circuit can be joined in two ways, and the way you choose changes how the whole circuit behaves.

Which circuit is this?

In a string of lights, when one bulb breaks every single bulb goes out. Which kind of circuit is it?

• Series, because there is only one path for the charge
• Parallel, with separate branches
• A magnetic circuit
• Not a circuit at all

How light reveals the universe

One of the most surprising ideas in physics is that we can learn about the whole universe just by studying light. When we look at light from a distant galaxy, we find it is stretched towards the red end of the spectrum, a change called red shift. The further away a galaxy is, the more its light is stretched, which tells us that distant galaxies are moving away from us, and the most distant ones fastest of all. The best explanation is that space itself is expanding, carrying the galaxies apart like spots on a balloon being blown up. Winding that expansion backwards led scientists to the idea that everything began, long ago, from a single hot, dense start. All of that comes from patiently reading the light that reaches us.

Pick the true facts about waves and circuits

Select every statement about P2 physics that is true.

• A wave carries energy without carrying matter along
• Light is part of the electromagnetic spectrum
• In a series circuit one break stops everything
• A wave moves matter all the way along with it
• A galaxy contains no stars

Order the steps to build a simple circuit

Put the steps of building and testing a simple lighting circuit into a sensible order.

• Start with a cell to push the charge
• Connect wires from the cell
• Add a bulb into the loop
• Add a switch to control it
• Close the switch to light the bulb

Complete the waves and electricity facts

The number of waves passing a point each second is the _____. The flow of electric charge around a circuit is the _____. The opposition to that flow, measured in ohms, is the _____. A coil of wire that becomes magnetic only while charge flows through it is an _____.

Tap the two electromagnetic waves

Read these four things. Tap the TWO that are part of the electromagnetic spectrum.

• radio waves
• visible light
• sound
• a bar magnet

Water flowing round a loop of pipes

A circuit is hard to picture because you cannot see charge moving, so imagine water flowing round a loop of pipes instead. A pump pushes the water round, just as a cell pushes charge round a circuit. If you fit a narrow section of pipe, the water finds it harder to get through and the flow drops, in the same way that a thin wire or a component makes the flow of charge harder. Widen the pipe and the water rushes round freely again. A tap in the loop is like a switch: open it and the water flows, close it and everything stops at once. Holding this picture in mind makes the numbers and the wiring far easier to reason about.

Work out the wave speed

A wave has a frequency of 5 hertz and a wavelength of 3 metres. Wave speed is the frequency times the wavelength. Work out the wave speed in metres per second. Give the number only.

Solve three P2 physics problems

Read each situation and choose the best answer.

• A circuit should let each bulb keep working even if another bulb fails. How should it be wired?
• The light from a distant galaxy is stretched towards the red end. What does this suggest?
• You want to make a magnet you can switch on and off. What do you build?

Build a waves and electricity point

Choose the word for each gap to complete one point about P2 physics.

Explain waves, electricity and space

A friend is revising P2 physics. Using what you have learned, explain the core ideas.

• Explain what a wave is and what the electromagnetic spectrum contains
• Explain the difference between a series and a parallel circuit
• Explain what current, voltage and resistance each mean
• Explain what an electromagnet is and one use for it
• Explain how red shift shows the universe is expanding