The shape of the lesson
By the end of the lesson, learners can
- Send them through a field: Pass each radiation through a field and watch which way, and how much, it bends.
- Charge and mass decide: The charge sets the direction; the mass sets how much it bends.
- Opposite charges: alpha and beta bend opposite ways.
- Mass: lighter beta bends more than heavier alpha.
- No charge: gamma is not deflected.
One picture every idea returns to
Because alpha is positive and beta is negative, they are deflected in opposite directions by electric and magnetic fields. Gamma has no charge, so it is not deflected. Beta is deflected far more than alpha because it has a much smaller mass.
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, Bent by charge, or not.. Send the three radiations through a magnetic field and they part company. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Send them through a field | Pass each radiation through a field and watch which way, and how much, it bends. Project tab 3 of the lab (Deflection in fields) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Charge and mass decide | The charge sets the direction; the mass sets how much it bends. | Mix-Pair-Share |
| 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, 13 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 Charge and mass decide, 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.
Mix-Pair-Share
Students mix around the room until you call pair; they pair with the nearest classmate, discuss the prompt, then mix again. Three prompts of rising difficulty, three different partners.
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 |
|---|---|
| Gamma is undeflected because it carries no charge. | Alpha and beta deflect in opposite directions because their charges are opposite, and beta deflects far more than alpha because it is so much lighter. |
Deflection of radiation in fields: worksheet
6 questions, 13 marks. Written in the style of the papers; no past paper question is reproduced.
A beam of alpha, beta and gamma radiation passes through a magnetic field. State how each one is affected.
Explain why alpha and beta radiation are deflected in opposite directions.
Although alpha has a larger charge than beta, beta is deflected much more. Explain why.
Explain why gamma radiation is not deflected by a magnetic or electric field.
A beam of beta particles enters the space between two charged plates, one positive and one negative. State which plate the beta is deflected towards, and why.
Three tracks are seen as radiation crosses a magnetic field: track P is straight, track Q curves gently, and track R curves sharply the other way. Identify each track and give a reason.
Answer key and marking notes
- Alpha is deflected slightly in one direction. ✓
- Beta is deflected more, in the opposite direction. ✓
- Gamma is not deflected. ✓
- Alpha is positively charged and beta is negatively charged. ✓
- The field pushes opposite charges in opposite directions. ✓
- Beta has a much smaller mass than alpha. ✓
- So the force changes the light beta’s direction far more than the heavy alpha’s. ✓
Gamma has no charge, so the field exerts no force on it. ✓
- Towards the positive plate. ✓
- Beta is negatively charged, and opposite charges attract. ✓
- P is gamma: it is not deflected because it has no charge. ✓
- Q is alpha: it is charged but heavy, so it bends only a little. ✓
- R is beta: it is light, so it bends a lot, in the opposite direction to alpha. ✓
4 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.
A beam containing alpha, beta, and gamma radiation passes through a magnetic field. Which radiation is not deflected at all?
- Agamma, because it has no charge
- Balpha, because it is the heaviest
- Cbeta, because it is the lightest
- Dall three are deflected equally
In an electric field, alpha and beta particles are deflected in opposite directions. Why?
- AThey carry opposite charges (alpha is positive, beta is negative).
- BThey have the same charge but different masses.
- COne is charged and the other is neutral.
- DThey travel at the same speed.
In the same field, why is the alpha particle deflected less than the beta particle?
- AThe alpha particle has a much greater mass, so it is harder to deflect.
- BThe alpha particle has no charge.
- CThe alpha particle moves much faster.
- DThe beta particle is positively charged.
Radiation passes between two charged plates. Which radiation bends toward the negative plate?
- Aalpha, because it is positively charged
- Bbeta, because it is positively charged
- Cgamma, because it has the most energy
- Dall of them equally
Quiz key
Gamma radiation has no charge, so a magnetic field exerts no force on it and it passes straight through. Alpha and beta are charged, so they are deflected (in opposite directions).
Alpha particles are positive and beta particles are negative, so the electric field pushes them in opposite directions. Their opposite charges, not their masses, set the directions.
The alpha particle is around 8000 times more massive than the beta particle, so for a similar force it deflects much less. Although alpha has a larger charge, its far greater mass dominates, giving a smaller deflection.
Alpha particles are positive, so they are attracted toward the negative plate. Beta (negative) bends the other way toward the positive plate, and gamma (no charge) passes straight through.
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.