--- title: "Where does static charge come from?" subtitle: "Year 9 Physics · Wave and particle models · Lesson 3" --- # Where does static charge come from? **Name:** {{field-24}} **Date:** {{field-15}} **Class:** {{field-15}} > **Key question:** Pull a woolly jumper over your head in the dark and you can see tiny sparks. Where does a spark come from? :::teacher-note **In one sentence:** Students explain static electricity as the transfer of electrons between materials that leaves a charge imbalance, and use it to explain attraction, repulsion and electrostatic discharge (AC9S9U04, node 3). **Students should be able to say:** I can say what moves when two materials are rubbed together. I can say which charges attract and which repel. I can explain what a spark is. **Width:** the unmarked parts are the floor every student does (Engage, Explore, Explain, Evaluate). Typical and Wider sections add contexts, not difficulty. Students work in the online tutorial alongside this sheet. ::: ## Engage :::keep-together **You rub a balloon on wool, and now the balloon is charged. What moved from one to the other?** ☐ Protons, from one material to the other ☐ Whole atoms ☐ Electrons, from one material to the other ☐ Nothing moved: rubbing made new charge My prediction, and why: {{lines-3}} ::: :::teacher-note **What happens:** Electrons. They are the only charges free to move. Protons are locked inside the nuclei. The material that gains electrons becomes negative; the one that loses them becomes positive. ::: ## Explore Try it on the board in the tutorial. Was your prediction right? What was different? {{lines-2}} ## Explain: charge and force :::keep-together ### Why positive **The wool ends up positively charged. Why?** ☐ It gained protons ☐ It lost electrons, so it has more + than − charge ☐ It made positive charge when rubbed ::: :::teacher-note **Answer:** It lost electrons, so it has more + than − charge Losing negative electrons leaves a surplus of positive charge from the protons that stayed behind. ::: :::keep-together ### Equal and opposite **The balloon gained 3 electrons from the wool. What is the wool's charge?** ☐ −3, the same as the balloon ☐ +3: it lost the 3 electrons the balloon gained ☐ 0, because charge cancels ::: :::teacher-note **Answer:** +3: it lost the 3 electrons the balloon gained No charge is created or destroyed: the balloon's −3 is balanced by the wool's +3, so the total is still zero. ::: :::keep-together ### Attract or repel **Do the two charged objects attract or repel?** Groups: Attract, Repel - A positive and a negative: {{field-15}} - Two negatives: {{field-15}} - Two positives: {{field-15}} ::: :::teacher-note **Answer:** A positive and a negative → Attract; Two negatives → Repel; Two positives → Repel ::: :::keep-together ### A spark **What is a spark, in terms of electrons?** ☐ Extra electrons rushing across to neutralise a charge imbalance ☐ Heat from friction ☐ Protons jumping across a gap ::: :::teacher-note **Answer:** Extra electrons rushing across to neutralise a charge imbalance When the charge imbalance is big enough, electrons jump the gap all at once to even things out: a spark, or on a huge scale, lightning. ::: :::typical ## Elaborate: push and pull :::keep-together ### Which feels more **Ball 1 is +3 and ball 2 is +1. What happens, and which ball feels the bigger force?** ☐ They repel, and ball 1 feels more ☐ They repel, and the force on each is the same size ☐ They attract, and ball 1 feels more ::: :::teacher-note **Answer:** They repel, and the force on each is the same size Like charges repel. The two forces are equal in size and opposite in direction, whatever the sizes of the charges. ::: ::: :::wider ## Elaborate: lightning :::keep-together **In a thunderstorm, ice and water particles rub past each other and charge builds up in the cloud. What is lightning?** ☐ Positive charge falling from the cloud ☐ A huge discharge: electrons rushing between the cloud and the ground (or another cloud) to neutralise the charge imbalance ☐ Heat energy escaping from the cloud ::: :::teacher-note **Answer:** A huge discharge: electrons rushing between the cloud and the ground (or another cloud) to neutralise the charge imbalance It is the same idea as the spark from the balloon, with far more charge and a much longer path. ::: ::: ## Evaluate: look back Write one sentence: "At first I thought… Now I think… because…" **Revision summary** - Atoms have **positive protons** that stay put and **negative electrons** that can move. - Rubbing moves **electrons** from one material to the other: one becomes positive, the other negative, by equal amounts. - **Unlike charges attract; like charges repel.** - A **spark** is the extra electrons rushing across to neutralise the imbalance. ## Exit ticket :::keep-together **A plastic ruler is rubbed on a cloth and becomes negative. What happened to the cloth, and why?** {{lines-3}} ::: :::teacher-note **Answer:** The cloth became positive. Electrons moved from the cloth to the ruler, so the cloth has more + than −. :::