In a conductor such as copper each atom lets go of an electron, so there are free electrons that can move. A battery pushes them round the circuit: this flow of charge is the current, and more volts push harder. In an insulator the electrons stay tied to their atoms, so there is no current. The electrons are not used up; the bulb transfers the battery's energy.
A copper wire and a plastic ruler both contain millions of electrons. Only one of them can light a bulb. What is different?
The last lesson was about charge standing still. Now it moves.
Engage: Commit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Explore: Try it on the board and compare what happens with your prediction.
Explain: Use the particle model to explain what you saw.
Elaborate: Use the same idea in a new context.
Evaluate: Look back at your first ideas and what changed.
WidthMore contexts, same idea.
Make your prediction first. Help opens once you've locked it in.
EngageCommit to a prediction before you test anything. A wrong guess is fine: it shows you what to look for.
Engage: what flows?
ExploreTry it on the board and compare what happens with your prediction.
Explore: wires and plastic
Use the slider or the + and − buttons. Watch how fast the blue electrons drift.
Try it yourselfYour edits are saved in this browser.
With copper wire, turn the battery up to 5 volts or more.
Use the board. This ticks when you get there.
Now choose the plastic strip. Does the bulb light?
Use the board. This ticks when you get there.
Go back to copper and turn the battery down to 0 V.
Use the board. This ticks when you get there.
ExplainUse the particle model to explain what you saw.
Explain: the particle model of current
In your book: draw a loop of wire with a battery and a bulb. Mark the electrons and the atoms, show the way the electrons move and the way conventional current is drawn, and write a caption about what the battery does.
Elaborate TypicalUse the same idea in a new context.
Elaborate: how bright?
Try it yourselfYour edits are saved in this browser.
With copper, set 1 V. Watch the drift and the glow. Then set 6 V.
Use the board. This ticks when you get there.
Elaborate WiderUse the same idea in a new context.
Elaborate: in between
EvaluateLook back at your first ideas and what changed.
Evaluate: look back
Write one sentence: "At first I thought… Now I think… because…"
Revision summary
A conductor has free electrons; an insulator has almost none: its electrons are held tightly by their atoms.
A current is a flow of free electrons. The battery pushes them round; more volts means a stronger push.
The electrons are not used up; the bulb transfers the energy they carry.
Conventional current is drawn the opposite way to the electrons, by a historical choice.
For teachers
Students explain electric current as a directed flow of free electrons driven by voltage, and distinguish conductors from insulators using free and bound electrons (AC9S9U04, node 3). About 25 minutes.
I can say why copper conducts and plastic doesn't.
I can say what the battery does.
Before class
A concept tutorial for introducing or revising the idea. Set the width with ?width=minimum, typical (default) or wider. It follows Where does static charge come from? and comes before the electromagnetic spectrum.
Students arrive from Year 6 circuits with a working model (current goes round, the bulb uses it up). The prediction targets 'electrons used up'. Don't introduce current as a number of amperes here; the Year 9 descriptor is about the particle model.
Board notes: the loop shows far fewer electrons than a real wire has, and drift is exaggerated. Real drift speed is a small fraction of a millimetre a second; the push travels round the loop almost at once, which is why the bulb lights immediately. The nearest neighbour atoms are drawn as fixed positive charges; real conductors have a 'sea' of free electrons around positive ions.
Running the lesson
Engage: tally the predictions. Ask the 'used up' group where the electrons go when they leave the bulb.
Explore: ask what is different about plastic that matters.
Explain: free versus bound and the battery's role are the success criteria.
In your own words: the loop diagram with both directions marked.
The hard part (on purpose)
That electrons aren't used up. When a student says the bulb eats electrons, ask them to count the electrons entering and leaving the bulb on the board.
When students get stuck
A student says current is used up in the bulb. Ask: Do fewer electrons leave the bulb than enter it? Fix: The same number leave. The bulb gets energy from them, not electrons.
A student says plastic has no electrons. Ask: Is plastic made of atoms? Fix: Yes, so it has electrons. They are tied to their atoms and can't move round.
A student says the battery makes electrons. Ask: Were there electrons in the wire before the battery was joined? Fix: Yes. The battery pushes the ones already there.
Stretch and support
Stretch: The push reaches the bulb almost at once, but each electron drifts very slowly. How can the bulb light straight away? (The wire is already full of electrons, so they all start moving together, like a full tube of marbles.)
Support: Give a drawn loop with the battery and bulb and ask students to add an arrow on each of three blue electrons, then to label the battery's + and − ends.
Where it leads
Next: What is the electromagnetic spectrum? The wave model is extended to light, which, unlike sound, doesn't need a medium.
In class: build a simple circuit and test materials as conductors or insulators; a lemon or potato cell; a hand-crank generator.
What each step is for
Engage: what flows?: Students often say electrons leave the battery and are used up in the bulb. The particle model says the free electrons are already in the wire, are pushed round, and are not used up.
Explore: wires and plastic: Switching between copper and plastic with the same battery isolates the one thing that matters, free electrons, and turning the volts up and down shows what the battery adds.
Explain: the particle model of current: Defining current as the flow of free electrons, distinguishing conductors and insulators by free versus bound electrons, and giving the battery's role covers the node's other two success criteria.
Elaborate: how bright?: Predicting what a bigger voltage does, then testing it, links the push to the drift speed and the energy delivered.
Elaborate: in between: Semiconductors blur the conductor and insulator line, and show that the free electron model is a starting point.