The shape of the lesson
By the end of the lesson, learners can
- Build a hadron: Combine up and down quarks and read off the total charge.
- Quarks and the particles: Charges add to give the particle charge.
- Baryons, mesons and leptons: Two families of matter, built very differently.
- Up: +2/3 e.
- Down: −1/3 e.
- Baryon: three quarks.
One picture every idea returns to
Protons and neutrons are not fundamental; they are made of quarks. The up quark has charge +2/3 e and the down quark −1/3 e. A proton is uud and a neutron is udd. Hadrons are particles made of quarks: baryons are three quarks (qqq) and mesons are a quark and an antiquark. In beta-minus decay a down quark changes to an up quark; in beta-plus an up changes to a down. Leptons, such as the electron and the neutrino, are fundamental and not made of quarks.
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, What the proton is made of.. The proton and neutron are not the end of the story: each is built from smaller particles called quarks. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 13 min | Teach and check: Build a hadron | Combine up and down quarks and read off the total charge. Project tab 4 of the lab (Quarks and leptons) and let a student drive it while the class predicts. | Whole class, then pairs |
| 13 to 21 min | Teach and check: Quarks and the particles | Charges add to give the particle charge. | Pairs |
| 21 to 30 min | Teach and check: Baryons, mesons and leptons | Two families of matter, built very differently. | 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 Baryons, mesons and leptons, 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 |
|---|---|
| Quark charges are fractional: up is +2/3 e and down is −1/3 e, and they add to give the whole-number charge of the particle. | A baryon is three quarks while a meson is a quark- antiquark pair, so do not confuse the two. Leptons (electron, neutrino) are fundamental: they are not made of quarks, unlike the proton and neutron. |
Quarks and leptons: worksheet
6 questions, 13 marks. Written in the style of the papers; no past paper question is reproduced.
State the charge on an up quark and on a down quark.
A proton has the quark composition uud. Show that its charge is +1 e.
A neutron has the quark composition udd. Show that its charge is zero.
State the difference between a baryon and a meson in terms of quark content.
In beta-minus decay a neutron changes into a proton. Describe the quark change involved and show it is consistent with the change in composition.
Name two leptons and state what makes them fundamental.
Answer key and marking notes
- Up quark: +2/3 e ✓
- Down quark: −1/3 e ✓
- Charge = (+2/3) + (+2/3) + (−1/3) e ✓
- = (+4/3 − 1/3) e = +1 e ✓
- Charge = (+2/3) + (−1/3) + (−1/3) e ✓
- = (+2/3 − 2/3) e = 0 ✓
- A baryon is made of three quarks (qqq) ✓
- A meson is made of a quark and an antiquark ✓
- A down quark changes into an up quark ✓
- udd (neutron) becomes uud (proton), which is the change from down to up in one quark ✓
- For example, the electron and the (electron) neutrino ✓
- They are fundamental because they are not made of quarks or any smaller particles ✓
14 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.
The charge on an up quark is:
- A+2/3 e
- B−1/3 e
- C+1 e
- D−1 e
The charge on a down quark is:
- A+2/3 e
- B−1 e
- C−1/3 e
- D0
A proton has the quark composition:
- Audd
- Buud
- Cuuu
- Dud
A neutron has the quark composition:
- Auud
- Bddd
- Cud
- Dudd
A baryon is composed of:
- Athree quarks
- Ba quark and an antiquark
- Ctwo quarks
- Donly leptons
A meson is composed of:
- Athree quarks
- Btwo quarks
- Ca quark and an antiquark
- Dthree leptons
In beta-minus decay, a down quark changes into:
- Aa strange quark
- Ban up quark
- Can electron
- Dan antiquark
In beta-plus decay, an up quark changes into:
- Aa strange quark
- Ba positron
- Ca neutrino
- Da down quark
The total charge of a neutron (udd) is:
- A0
- B+1 e
- C−1 e
- D+2/3 e
The total charge of a proton (uud) is:
- A0
- B+2 e
- C+1 e
- D−1 e
Which of these is a lepton?
- Athe proton
- Bthe electron
- Cthe neutron
- Dthe alpha particle
Which of these is NOT a hadron?
- Athe proton
- Bthe neutron
- Ca meson
- Dthe electron
Leptons such as electrons and neutrinos are:
- Afundamental particles, not made of quarks
- Bmade of three quarks
- Cmade of a quark and antiquark
- Dthe same as baryons
The number of different quark flavours is:
- Athree
- Btwo
- Csix
- Dtwelve
Quiz key
Up quark: +2/3 e.
Down quark: −1/3 e.
A proton is uud.
A neutron is udd.
Baryons are three quarks (qqq).
Mesons are a quark-antiquark pair.
Beta-minus: d → u, turning a neutron into a proton.
Beta-plus: u → d, turning a proton into a neutron.
+2/3 − 1/3 − 1/3 = 0.
+2/3 + 2/3 − 1/3 = +1 e.
The electron is a lepton; the others are composite.
The electron is a lepton, not a hadron; protons, neutrons and mesons are hadrons.
Leptons are fundamental and contain no quarks.
There are six quark flavours: up, down, strange, charm, top and bottom.
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.