The shape of the lesson
By the end of the lesson, learners can
- Charge it by rubbing: Transfer electrons between objects and watch the charges attract or repel.
- It is the electrons that move: Charging by friction shifts electrons from one surface to the other.
- The rule: like charges repel, unlike charges attract.
- Friction: rubbing transfers electrons. Gain electrons, become negative; lose electrons, become positive.
- Conserved: the two objects gain equal and opposite charge.
One picture every idea returns to
There are two types of charge, positive and negative. Like charges repel and unlike charges attract. Rubbing two insulators together transfers electrons: the one that gains electrons becomes negative, the one that loses them becomes positive.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, Two charges, one rule.. Rub a balloon on your hair and it sticks to the wall and lifts your hair toward it. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Charge it by rubbing | Transfer electrons between objects and watch the charges attract or repel. Project tab 1 of the lab (Static electricity bench) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: It is the electrons that move | Charging by friction shifts electrons from one surface to the other. | Anticipation / Reaction Guide |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 15 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in It is the electrons that move, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Anticipation / Reaction Guide
Before the lesson, students mark five statements true or false. After the teaching they mark them again and justify any change of mind in one sentence each. The statements come from the examiner traps below.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| It is electrons that move, not positive charge. | The object that gains electrons becomes negatively charged, and the one that loses electrons is left positive. |
Electric charge: worksheet
6 questions, 15 marks. Written in the style of the papers; no past paper question is reproduced.
State what happens to the force between each pair of charges.
(a) Two negatively charged spheres.
(b) A positively charged sphere and a negatively charged sphere.
An acetate rod is rubbed with a dry cloth and becomes positively charged. Explain, in terms of electrons, why the rod becomes positive and state the charge left on the cloth.
A student says, "When you rub a balloon it gains positive charge, and some of that charge then flows away through the air." Identify the two errors in this statement.
Sort the following into conductors and insulators: copper, plastic, graphite, rubber.
A negatively charged rod is held near small pieces of uncharged paper, and the paper jumps up to the rod. The rod is not touching the paper.
Explain why the uncharged paper is attracted.
Two light balls hang side by side on insulating threads. A charged rod is used to give both balls a negative charge, and they swing apart and stay apart.
(a) State why the balls swing apart.
(b) A third ball, known to be uncharged, is brought near one of them. State and explain what is observed.
Answer key and marking notes
(a) They repel. ✓
(b) They attract. ✓
like repel, unlike attract
- The rod loses electrons to the cloth. ✓
- Having lost negative electrons, the rod is left positively charged. ✓
- The cloth gains those electrons, so it becomes negatively charged. ✓
- Charge is gained by transferring electrons, not by gaining positive charge; only electrons move. ✓
- Air is an insulator, so the charge does not flow away through it; that is why the balloon stays charged. ✓
Conductors: copper, graphite. ✓
Insulators: plastic, rubber. ✓
- The negative rod repels electrons in the paper, pushing them to the far side. ✓
- This leaves the near side of the paper positively charged (an induced charge). ✓
- The near positive side is closer to the rod than the far negative side, so the attraction wins and the paper is pulled in. ✓
(a) Both balls carry the same (negative) charge, and like charges repel. ✓
(b) The charged ball attracts the uncharged ball, by inducing an opposite charge on its near side. ✓✓
2 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
Two light balls hang on threads. Both are given a negative charge and they swing apart. What does this show?
- ALike charges repel each other.
- BLike charges attract each other.
- CNegative charges have no effect on each other.
- DThe balls are too heavy to hang straight.
A plastic rod becomes negatively charged when rubbed with a cloth. What has actually moved?
- AElectrons moved from the cloth onto the rod.
- BProtons moved from the cloth onto the rod.
- CElectrons moved from the rod onto the cloth.
- DPositive charges flowed along the rod.
Quiz key
Two negative (like) charges repel, pushing the balls apart. Unlike charges would attract and pull the balls together.
Only electrons are free to move; the rod becoming negative means it gained electrons from the cloth. Protons are fixed in the nuclei and do not transfer during rubbing.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.