---
marp: true
theme: default
html: true
---

# How does current flow?

Year 9 Physics · Wave and particle models

<!-- Speaker note: 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 (Engage and Explore 8 min · Explain 11 min · Evaluate 3 min · Typical adds 3 min, Wider about 2 min). -->

---

## Today

**We are learning to** 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.

- I can explain what an electric current is.
- I can say why copper conducts and plastic doesn't.
- I can say what the battery does.

<!-- Speaker note: 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. Teacher: In your own words: the loop diagram with both directions marked. -->

---

## Why it matters

> A copper wire and a plastic ruler both contain millions of electrons. Only one of them can light a bulb. What is different?

<!-- Speaker note: The last lesson was about charge standing still. Now it moves. -->

---

<span style="background:#dbeafe; color:#1a1a1a; border:1.5px solid #3b82f6; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">💬 Discussion</span>

## Engage: predict

**A battery is joined to a bulb by copper wire and the bulb lights. What is flowing round the circuit?**

- Electrons that were already in the wire, pushed round by the battery
- Electrons that come out of the battery and are used up in the bulb
- Nothing flows: the bulb makes the electricity
- Protons, pushed round by the battery

<!-- Speaker note: What happens: Electrons that were already in the wire. A metal is full of free electrons; the battery pushes them round the loop. They are not used up: as many go back into the battery as come out. What the bulb uses is the energy they carry. Take two or three predictions before anyone runs it. -->

<!-- Speaker note: Teacher: tally the predictions. Ask the 'used up' group where the electrons go when they leave the bulb. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 28px; }</style>

---

<span style="background:#fef3c7; color:#1a1a1a; border:1.5px solid #f59e0b; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✍️ Activity</span>

## Explore it

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-board/index.html?id=deck%2Fscience%2Fphysics-9%2Felectric-current%2Fstep-2&code=widget%3A+charge%0Amode%3A+current%0Amaterial%3A+choose%0Avolts%3A+2%0A&fresh=1}}

[Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/physics-9/electric-current/?full=step-2#step-2)

<!-- Speaker note:  -->

<!-- Speaker note: Teacher: ask what is different about plastic that matters. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 25px; }</style>

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## What happened?

* Electrons that were already in the wire. A metal is full of free electrons; the battery pushes them round the loop. They are not used up: as many go back into the battery as come out. What the bulb uses is the energy they carry.

<!-- Speaker note: Reveal after running. Ask who predicted it, and what made them think so. -->

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Current

**What is an electric current in a metal wire?**

- A flow of free electrons
- A flow of atoms
- A flow of protons

* Answer: A flow of free electrons

<!-- Speaker note: The atoms are fixed; the free electrons between them drift along when pushed. -->

<!-- Speaker note: Teacher: free versus bound and the battery's role are the success criteria. -->

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Conductor and insulator

**Why does copper conduct while plastic doesn't?**

- Copper has free electrons that can move; in plastic they are tied to their atoms
- Copper has more protons
- Plastic has no electrons

* Answer: Copper has free electrons that can move; in plastic they are tied to their atoms

<!-- Speaker note: Conductors have many free electrons; in insulators almost all the electrons are held tightly by their atoms. -->

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## The battery

**What does the battery do?**

- Stores electrons and releases them until it is empty
- Makes the electrons
- Pushes the free electrons round the circuit, giving them energy

* Answer: Pushes the free electrons round the circuit, giving them energy

<!-- Speaker note: The battery's voltage is the push. A bigger voltage pushes harder, so the electrons drift faster and more energy is delivered each second. -->

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Used up?

**Are the electrons used up in the bulb?**

- Only some of them
- Yes: that is where the light comes from
- No: the same number go in as come out; the bulb transfers the energy they carry as light and heat

* Answer: No: the same number go in as come out; the bulb transfers the energy they carry as light and heat

<!-- Speaker note: Current is the same at every point in the loop; the energy, not the electrons, is what the bulb gets. -->

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Which way

**On the board, electrons drift round one way. By convention the current is drawn the other way. Why?**

- The convention was chosen before electrons were discovered, and has stuck
- The board has a mistake
- Current is the flow of protons

* Answer: The convention was chosen before electrons were discovered, and has stuck

<!-- Speaker note: Conventional current is drawn from + to −, a choice made before electrons were known. Electrons actually flow the other way. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 28px; }</style>

---

<span style="background:#fef3c7; color:#1a1a1a; border:1.5px solid #f59e0b; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✍️ Activity</span>

## Elaborate: how bright?

{{embed: https://studio.learningwaypoints.com/tutorials/_playground-board/index.html?id=deck%2Fscience%2Fphysics-9%2Felectric-current%2Fstep-4&code=widget%3A+charge%0Amode%3A+current%0Amaterial%3A+choose%0Avolts%3A+2%0A&fresh=1}}

[Open this step in the tutorial](https://studio.learningwaypoints.com/tutorials/science/physics-9/electric-current/?full=step-4#step-4)

<!-- Speaker note: What this step is for: Predicting what a bigger voltage does, then testing it, links the push to the drift speed and the energy delivered. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 25px; }</style>

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## What changes

**What happens to the electrons and the bulb when the voltage doubles?**

- The electrons get bigger
- The electrons drift faster, the current is bigger and the bulb is brighter
- Nothing changes: the bulb has a fixed brightness

* Answer: The electrons drift faster, the current is bigger and the bulb is brighter

<!-- Speaker note: More volts means a stronger push. The electrons drift faster, so more charge passes each second and more energy reaches the bulb. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 28px; }</style>

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Elaborate: in between

**Silicon has only a few free electrons, far fewer than copper and far more than plastic. It is used in computer chips. Why is that useful?**

- It is a perfect insulator
- It is cheap
- Its conduction can be controlled (by adding other atoms, or a voltage), so it can act as a switch

* Answer: Its conduction can be controlled (by adding other atoms, or a voltage), so it can act as a switch

<!-- Speaker note: A material that sits between conductors and insulators can be switched on and off, which is how transistors in chips work. What this step is for: Semiconductors blur the conductor and insulator line, and show that the free electron model is a starting point. -->

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 26px; }</style>

---

## 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.

<style scoped>pre, marp-pre { font-size: 0.5em; line-height: 1.25; } section { font-size: 26px; }</style>

---

<span style="background:#dcfce7; color:#1a1a1a; border:1.5px solid #22c55e; padding:6px 18px; border-radius:8px; font-size:1em; font-weight:500;">✅ Check</span>

## Exit ticket

**A student says 'the bulb uses up the electrons so the wire after it is empty'. What would you say?**

* The same number of electrons leave the bulb as enter it. They carry on round the loop. The bulb transfers some of the energy they carry as light and heat.

<!-- Speaker note: Students answer on paper or a mini whiteboard before the reveal. Anyone who cannot answer needs the main idea again next lesson. Where this 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. -->