Unit 11 · Quantum and Nuclear Physics
The Complete Cambridge International AS & A Level Physics (9702) Guide · Cambridge International AS & A Level Physics (9702)Unit 11 · Quantum and Nuclear Physics
- The Complete Cambridge International AS & A Level Physics (9702) Guide
- Cambridge International AS & A Level Physics (9702)
- 12 sections
Cambridge International does not publish a per-unit weighting for this exam. Exam structure (official): AS Level: Multiple Choice (75 min, 40 questions, 31%) · AS Level Structured Questions (75 min, 46%) · Advanced Practical Skills (120 min, 2 questions, 23%); A Level: Multiple Choice (75 min, 40 questions, 15.5%) · AS Level Structured Questions (75 min, 23%) · Advanced Practical Skills (120 min, 2 questions, 11.5%) · A Level Structured Questions (120 min, 38.5%) · Planning, Analysis And Evaluation (75 min, 2 questions, 11.5%). Be ready to carry the same unit skills and representations into a complete answer on every paper. A 400 nm wavelength gives photon energy 4.97 × 10⁻¹⁹ J, equivalent to 3.11 eV. Keeping the conversion outside the energy subtraction avoids mixing joules and electronvolts.
- How Cambridge International AS & A Level Physics (9702) assesses this Cambridge International publishes no per-unit percentage for Cambridge International A Level Physics; Paper 1 accounts for 31% of the AS Level total and 15.5% of the A Level total. · AS Level: Multiple Choice (75 min, 40 questions, 31%) · AS Level Structured Questions (75 min, 46%) · Advanced Practical Skills (120 min, 2 questions, 23%) | A Level: Multiple Choice (75 min, 40 questions, 15.5%) · AS Level Structured Questions (75 min, 23%) · Advanced Practical Skills (120 min, 2 questions, 11.5%) · A Level Structured Questions (120 min, 38.5%) · Planning, Analysis And Evaluation (75 min, 2 questions, 11.5%) · show the model with A graph of maximum energy (eV) against frequency (10¹⁴ Hz)., A formula card that explains the photoelectric equation separates the work function from surplus electron kinetic energy., A table linking key concept, why it matters, visible method.
- Key skills Photon Energy and Momentum and the Photoelectric Effect (A Level), Wave-Particle Duality and the de Broglie Wavelength (A Level), Energy Levels in Atoms and Line Spectra (A Level), Mass Defect, Nuclear Binding Energy, Fission and Fusion (A Level), Radioactive Decay: Activity, Decay Constant and Half-Life (A Level)
- How to study for Unit 11 This page turns A graph of maximum energy (eV) against frequency (10¹⁴ Hz)., A formula card that explains the photoelectric equation separates the work function from surplus electron kinetic energy., A table linking key concept, why it matters, visible method. into one route: Evaluate hc/λ.
- The organizing decision Choose either joules or electronvolts for the subtraction, then convert the completed energy result if the other unit is required.
What Cambridge International AS & A Level Physics (9702) Unit 11 covers
Use this map to connect each assessed skill to the relationship or representation that makes it visible.
Photon Energy and Momentum and the Photoelectric Effect (A Level)
de Broglie wavelength; mass defect; activity02Wave-Particle Duality and the de Broglie Wavelength (A Level)
de Broglie wavelength; mass defect; activity03Energy Levels in Atoms and Line Spectra (A Level)
de Broglie wavelength; mass defect; activity04Mass Defect, Nuclear Binding Energy, Fission and Fusion (A Level)
de Broglie wavelength; mass defect; activity05Radioactive Decay: Activity, Decay Constant and Half-Life (A Level)
de Broglie wavelength; mass defect; activityCambridge International does not publish a per-unit weighting for this exam.
Official unit name and weighting: Cambridge International syllabus.
Quantum and Nuclear Physics
Connect the published share to the unit model
A 400 nm wavelength gives photon energy 4.97 × 10⁻¹⁹ J, equivalent to 3.11 eV. Keeping the conversion outside the energy subtraction avoids mixing joules and electronvolts.
Subtracting the 2.20 eV work function leaves 0.91 eV of maximum kinetic energy. In joules, that surplus is 1.46 × 10⁻¹⁹ J.
Emission occurs because the photon energy exceeds the work function. Below threshold, changing intensity would not replace the missing energy per photon.
Identify the quantum or nuclear conservation relation before converting wavelength, frequency, mass or energy units. In photoelectric work, separate the threshold energy from the surplus available as kinetic energy. In decay work, apply the exponential relation and interpret the result as a statement about activity, half-life or probability.
The decision that organizes this unit
Define the system and choose the route before calculating
Choose either joules or electronvolts for the subtraction, then convert the completed energy result if the other unit is required.
Evaluate hc/λ
Mechanism route and repair branches
Relationships to preserve
- Photon: Wavelength is 400 × 10⁻⁹ m.
- Threshold: The surface needs 2.20 eV.
- Surplus: Available kinetic energy is the difference.
Representations to read
- A graph of maximum energy (eV) against frequency (10¹⁴ Hz).
- A formula card that explains the photoelectric equation separates the work function from surplus electron kinetic energy.
- A table linking key concept, why it matters, visible method.
Branches to reject
- Using 400 without the nano prefix
- Combining 4.97 × 10⁻¹⁹ J directly with 2.20 eV
- Treating the axis labels as unscaled hertz
| Key concept | Why it matters | Visible method |
|---|---|---|
| Photon | Wavelength is 400 × 10⁻⁹ m | Evaluate hc/λ |
| Threshold | The surface needs 2.20 eV | Compare 3.11 eV with the work function |
| Surplus | Available kinetic energy is the difference | Report 0.91 eV or 1.46 × 10⁻¹⁹ J |
| One energy unit | Threshold and surplus energy must be compared consistently. | Convert before subtracting work function from photon energy. |
| Physical interpretation | A positive surplus establishes emission and maximum kinetic energy. | State the threshold conclusion after the calculation. |
How Cambridge International AS & A Level Physics (9702) assesses Quantum and Nuclear Physics
What a complete response must make visible
Match the task to evidence that a reader can audit, then check the most likely reasoning failure before finalizing the response.
| Task | Evidence to show | Hurdle |
|---|---|---|
| Photon Energy and Momentum and the Photoelectric Effect (A Level) | de Broglie wavelength; mass defect; activity | Using 400 without the nano prefix |
| Wave-Particle Duality and the de Broglie Wavelength (A Level) | de Broglie wavelength; mass defect; activity | Combining 4.97 × 10⁻¹⁹ J directly with 2.20 eV |
| Energy Levels in Atoms and Line Spectra (A Level) | de Broglie wavelength; mass defect; activity | Treating the axis labels as unscaled hertz |
| Mass Defect, Nuclear Binding Energy, Fission and Fusion (A Level) | de Broglie wavelength; mass defect; activity | Using 400 without the nano prefix |
| Radioactive Decay: Activity, Decay Constant and Half-Life (A Level) | de Broglie wavelength; mass defect; activity | Combining 4.97 × 10⁻¹⁹ J directly with 2.20 eV |
Worked example: photons, thresholds, decay and binding energy
Read each question as it appears on the exam paper, choose your answer, then tap it to see the feedback.
Practice 1: Photoelectric maximum kinetic energy
Monochromatic light strikes a metal surface.
Light of wavelength 400 nm strikes a surface with work function 2.20 eV. Calculate the maximum photoelectron kinetic energy and state whether emission occurs.
[4]Show all necessary working.
A. E = 3.11 eV, so Kₘₐₓ = 0.91 eV and emission occurs.
✅ Correct! 😊 Correct. The photon energy exceeds the 2.20 eV work function, leaving 0.91 eV as maximum kinetic energy.
B. Kₘₐₓ = 2.20 − 3.11 = −0.91 eV, so emission does not occur.
❌ Not quite 😭 This reverses the photoelectric energy balance. Kinetic energy is photon energy minus work function.
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C. Kₘₐₓ = 3.11 + 2.20 = 5.31 eV.
❌ Not quite 😭 The work function is energy required to escape and must be subtracted from photon energy, not added.
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D. Kₘₐₓ = 4.97 × 10⁻¹⁹ − 2.20 = −2.20 J.
❌ Not quite 😭 This subtracts a value in electronvolts directly from one in joules. Both energies must first use the same scale.
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Full explanation
- Step 1Convert λ = 400 nm to 400 × 10⁻⁹ m and use E = hc/λ.
- Step 2Calculate E = 4.97 × 10⁻¹⁹ J = 3.11 eV.
- Step 3Use Kₘₐₓ = E − φ = 3.11 − 2.20 = 0.91 eV.
- Step 4Because E exceeds φ, emission occurs; 0.91 eV = 1.46 × 10⁻¹⁹ J.
Practice 2: Radioactive half-life
A radioactive sample has a constant half-life.
A sample's activity falls from 800 Bq to 100 Bq in 18 hours. Determine its half-life.
[3]Show all necessary working.
A. There are three half-lives, so the half-life is 6.0 h.
✅ Correct! 😊 Correct. The sequence 800 → 400 → 200 → 100 contains three halvings in 18 hours.
B. There are eight half-lives, so the half-life is 2.25 h.
❌ Not quite 😭 The ratio 800/100 is eight, but the number of half-lives is the power of two giving that ratio, not the ratio itself.
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C. There is one half-life, so the half-life is 18 h.
❌ Not quite 😭 After one half-life the activity would be 400 Bq, not 100 Bq. Further halvings are required.
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D. There are four half-lives, so the half-life is 4.5 h.
❌ Not quite 😭 Four half-lives would reduce 800 Bq to 50 Bq. The observed final activity is reached after only three.
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Full explanation
- Step 1Track successive halvings: 800 Bq becomes 400 Bq after one half-life.
- Step 2A second half-life gives 200 Bq, and a third gives 100 Bq.
- Step 3Thus 18 hours corresponds to three half-lives.
- Step 4Calculate t½ = 18 h/3 = 6.0 h.
Key terms for Unit 11: Quantum and Nuclear Physics
Models, uses, and boundaries
- Quantum and Nuclear Physics
- The photoelectric equation separates the work function from surplus electron kinetic energy. Use this relationship when the photoelectric equation separates the work function from surplus electron kinetic energy..
- Worked example: photons, thresholds, decay and binding energy
- Photon energy is converted to eV before the 2.20 eV work function is subtracted. Use this relationship when photon energy is converted to eV before the 2.20 eV work function is subtracted..
- Quantum and Nuclear Physics: change one condition
- Higher frequencies on the line provide larger maximum energy above the same threshold. Use this relationship when higher frequencies on the line provide larger maximum energy above the same threshold..
- Quantum and Nuclear Physics: test proposed results
- A proposed emission result must place photon energy above the stated work function. Use this relationship when a proposed emission result must place photon energy above the stated work function..
Cambridge International AS & A Level Physics (9702) Unit 11 FAQ
How much of Cambridge International AS & A Level Physics (9702) does Unit 11 carry?
Cambridge International does not publish a per-unit weighting for this exam.
What is the first move on a Quantum and Nuclear Physics problem?
Evaluate hc/λ
Which relationships should I preserve?
Photon: Wavelength is 400 × 10⁻⁹ m. Threshold: The surface needs 2.20 eV. Surplus: Available kinetic energy is the difference.
Which representations should I practice?
Practice moving among A graph of maximum energy (eV) against frequency (10¹⁴ Hz)., A formula card that explains the photoelectric equation separates the work function from surplus electron kinetic energy., A table linking key concept, why it matters, visible method..
What error should I check before submitting an answer?
Check for Using 400 without the nano prefix; Combining 4.97 × 10⁻¹⁹ J directly with 2.20 eV; Treating the axis labels as unscaled hertz.
Evidence workshop
Continue from the free model into complete practice
The full unit guide continues with the chapter’s worked examples, figures, scoring tables, and answer checks.
- Worked example: photons, thresholds, decay and binding energy
- Quantum and Nuclear Physics: change one condition
- Quantum and Nuclear Physics: test proposed results
- Check the worked-example evidence for Quantum and Nuclear Physics
Full unit practice. Open the complete guide for the full evidence workshop and synthesis.
Related Cambridge International AS & A Level Physics (9702) unit guides
Cambridge International AS & A Level Physics (9702) Exam Guide & Review
The whole exam and its official unit sequence.01Physical Quantities and Units
Cambridge International does not publish a per-unit weighting for this exam.02Kinematics and Dynamics
Cambridge International does not publish a per-unit weighting for this exam.03Forces, Energy and Deformation of Solids
Cambridge International does not publish a per-unit weighting for this exam.04Waves and Superposition
Cambridge International does not publish a per-unit weighting for this exam.05Electricity and D.C. Circuits
Cambridge International does not publish a per-unit weighting for this exam.06Particle Physics
Cambridge International does not publish a per-unit weighting for this exam.07Circular Motion, Gravitational Fields and Oscillations
Cambridge International does not publish a per-unit weighting for this exam.08Thermal Physics
Cambridge International does not publish a per-unit weighting for this exam.09Electric Fields and Capacitance
Cambridge International does not publish a per-unit weighting for this exam.10Magnetic Fields and Alternating Currents
Cambridge International does not publish a per-unit weighting for this exam.12Medical Physics, Astronomy and Cosmology
Cambridge International does not publish a per-unit weighting for this exam.How to study Cambridge International AS & A Level Physics (9702) Unit 11
Start with the organizing decision
Before solving, restate the decision in operational terms: Choose either joules or electronvolts for the subtraction, then convert the completed energy result if the other unit is required.. Your first written move should be to Evaluate hc/λ.
Practice the same idea in several representations
Rotate through A graph of maximum energy (eV) against frequency (10¹⁴ Hz)., A formula card that explains the photoelectric equation separates the work function from surplus electron kinetic energy., A table linking key concept, why it matters, visible method.. Use each representation to practice Photon Energy and Momentum and the Photoelectric Effect (A Level), Wave-Particle Duality and the de Broglie Wavelength (A Level), Energy Levels in Atoms and Line Spectra (A Level), Mass Defect, Nuclear Binding Energy, Fission and Fusion (A Level), Radioactive Decay: Activity, Decay Constant and Half-Life (A Level), and explain what stays invariant when the surface form changes.
Turn each error into a repair check
After every attempt, audit the response for Using 400 without the nano prefix; Combining 4.97 × 10⁻¹⁹ J directly with 2.20 eV; Treating the axis labels as unscaled hertz. Then redo only the first step that made the reasoning diverge, keeping units, direction, and model conditions visible.
Confirm current course details in the official Cambridge International syllabus for the 2025-2027 administration.
Where to go next
Return to the Cambridge International AS & A Level Physics (9702) to see every unit and plan your revision.