Electricity and Magnetism

In Grade 6 you learned that electricity flows in a complete loop. Now you can describe what is flowing and what makes it move.

Current is the flow of electric charge around a circuit. The bigger the current, the more charge passes each second. Current is measured in amperes, usually shortened to amps ($A$).

Voltage is the push that drives the current around the circuit. It comes from the cell or battery. A bigger voltage gives a stronger push, so more current flows. Voltage is measured in volts ($V$).

A water analogy makes this clear: imagine water flowing round a loop of pipe.

• The current is like the flow of water — how much water moves past each second.
• The voltage is like a pump pushing the water round — the harder it pushes, the faster the water flows.

So voltage and current work together: the voltage of the cell pushes, and the current is the flow that results.

In Grade 6 you met series circuits — every component in a single loop. Now meet the other main type: the parallel circuit.

In a parallel circuit the path splits into two or more branches. Each component sits on its own branch, so the current can take more than one route.

The wiring choice changes how the circuit behaves:

• In a series circuit, the current is the same everywhere in the single loop. If one bulb breaks, the loop is broken and all the bulbs go out.
• In a parallel circuit, the current splits between the branches. Each bulb stays at full brightness, and if one branch breaks, the others keep working.

This is why the lights in your home are wired in parallel: switching off one lamp does not turn off the rest.

Now look more closely at the current in each type of circuit — this is one of the most useful ideas in this topic.

In a series circuit, there is only one path, so the current has nowhere else to go. The current is exactly the same at every point in the loop. It is not 'used up' as it passes through a bulb.

In a parallel circuit, the current reaches a junction and splits between the branches. More current goes down the easier branch. After the branches, the currents rejoin. The total current leaving the cell equals the sum of the currents in the branches.

So the key rule is: in series the current is shared along the loop equally everywhere; in parallel the current is split between the branches and adds back up.

To investigate circuits properly you need to measure them. Two meters do this job.

An ammeter measures the current. Because it must measure the flow passing through a point, it is connected in series — placed directly in the loop so the current flows through it. Its symbol is a circle with the letter A.

A voltmeter measures the voltage across a component. It is connected in parallel — placed across the component, on its own branch, like a bridge. Its symbol is a circle with the letter V.

A simple way to remember it: an Ammeter goes Along the loop (series); a Voltmeter is placed V across a component (parallel).

Here is one of the most important discoveries in physics: electricity and magnetism are linked. When an electric current flows through a wire, it creates a magnetic field around the wire.

If you wind the wire into a coil and place a piece of iron inside it, you build an electromagnet — a magnet that you can switch on and off.

An electromagnet has big advantages over an ordinary bar magnet:

• it can be switched on and off — break the circuit and the magnetism stops,
• its strength can be changed — more current, more coils, or a larger iron core all make it stronger,
• its poles can be reversed by reversing the current direction.

These features make electromagnets incredibly useful: scrapyard cranes lift and drop cars, doorbells and electric motors all rely on them.

So far you have studied current electricity — charge flowing round a circuit. But charge can also build up and stay still. This is static electricity.

Static is created by rubbing two materials together. The rubbing transfers tiny charged particles from one material to the other, so one becomes positively charged and the other negatively charged.

You have probably noticed static already:

• a balloon rubbed on a jumper sticks to a wall,
• a comb pulled through dry hair makes the hair stand on end,
• you feel a tiny shock touching a metal door handle.

There is a simple rule for charged objects, much like magnetic poles:

• like charges repel — two positives push apart, two negatives push apart,
• unlike charges attract — a positive and a negative pull together.

That is why hairs charged the same way all repel each other and spread out — and why a charged balloon is attracted to your hair. Lightning is static electricity on a giant scale: charge builds up in a storm cloud until it suddenly jumps as a huge spark.

The Stage 8 ideas in this topic open up a lot of later science:

• Resistance and Ohm's law — you will link current and voltage with a clear rule.
• Electrical power and energy — you will calculate how much energy appliances use.
• Motors and generators — these machines use the link between electricity and magnetism.
• Electrical safety — understanding circuits, fuses and earthing keeps you safe.
• Modern technology — phones, computers and electric vehicles all rely on these ideas.

Whenever a circuit puzzles you later, ask two questions: is this series or parallel? and what is the current doing? And remember the big idea — electricity and magnetism are two sides of the same story. Take your time here; these ideas power the modern world.