Aiming for an A* in A-Level Physics: Tackling Key Difficulties in Cambridge 9702 Paper 4 and How to Approach Paper 5 Experimental Planning

For the AS component of Cambridge A-Level Physics (9702), many Chinese students can score high relying on their foundation from domestic high school physics; however, scores often drop in the A Level component. There are two main reasons: first, Paper 4 tests topics that are rarely or superficially covered in domestic high schools, such as capacitance, the Hall effect, medical physics, and astrophysics; second, Paper 5, the "written practical paper," requires students to design experiments, draw diagrams, and calculate uncertainties, which many students haven't systematically practiced. Based on the official 9702 syllabus from Cambridge International, this article focuses specifically on how to prepare for the A Level component. For the breakdown of the five papers in 9702 and how to choose between it and Edexcel IAL Physics, see our guide on how Cambridge A-Level Physics is assessed.

1. What is Tested in the A Level Component

These two papers together account for half of the total A Level grade. There are two key points to note:

• Paper 4 will test AS content: The syllabus states that questions focus mainly on A Level content but require knowledge from the AS component; the AS learning outcomes are considered "assumed knowledge" for the A Level component. Therefore, you cannot drop AS after the AS exams;
• Paper 5 does not involve a lab: It is a written paper, but the syllabus emphasizes that candidates need extensive hands-on practical experience at the A Level to learn how to plan experiments.

Cambridge has released the new syllabus for 2028–2030, and the official statement indicates no major changes that would affect teaching.

2. Paper 4: 14 Topics in the A Level Content

The A Level component of the syllabus covers Chapters 12 to 25:

3. Key Difficulties Chinese Students Need to Focus On

The following lists the specific requirements of the syllabus; the judgments on what is "rarely covered in domestic schools" are based on our teaching experience.

1. Electric and Gravitational Fields: Study Them Together

The syllabus requirements for both fields are almost identical in structure: field strength, fields of point charges/point masses, and potential (electric potential, gravitational potential). The gravitational field section also requires analyzing circular orbits using gravity as the centripetal force, and understanding why geostationary satellites always remain above the same point on the Earth's surface.

How to study (empirical advice): Create a comparison table for "Electric vs. Gravitational Fields," placing the defining equations, point source formulas, potential expressions, and signs side by side. The most common confusions are the signs of potential and distinguishing between the three concepts of "potential energy, potential, and field strength."

2. Capacitance

Syllabus requirements: Derive formulas for capacitors in series and parallel from C = Q/V; energy stored in a capacitor; discharge of a capacitor through a resistor, and memorize and use the time constant τ = RC.

How to study: The discharge curve is an exponential decay, which is the same mathematical form as nuclear decay and the attenuation of ultrasound/X-rays. Practice the exponential equations from these areas together, including taking the natural logarithm to plot a straight line.

3. Magnetic Fields and Electromagnetic Induction

Syllabus requirements include: the force on a current-carrying conductor and moving charges in a magnetic field; the origin of the Hall voltage, deriving and using V_H = BI/(ntq), and using a Hall probe to measure magnetic flux density; magnetic fields produced by currents; Faraday's law and Lenz's law.

How to study: The Hall effect is rarely explained in detail in domestic high schools. You need to be able to derive the formula step by step from "charge carriers deflected by magnetic force, accumulating charge on both sides, and the balance between electric and magnetic forces," rather than just memorizing the result.

4. Alternating Currents

Syllabus requirements: characteristic quantities of alternating currents; using graphs to distinguish between half-wave and full-wave rectification; explaining half-wave rectification with a single diode and bridge rectification with four diodes; and smoothing.

How to study: Draw the bridge rectifier circuit yourself, labeling the current paths for the positive and negative half-cycles separately.

5. Quantum Physics

Syllabus requirements: energy and momentum of photons; the photoelectric effect (explained using photon energy and work function; explain why the maximum kinetic energy of photoelectrons is independent of light intensity, while the photoelectric current is proportional to it); wave-particle duality—the photoelectric effect is evidence for the particle nature of electromagnetic radiation, and the de Broglie wavelength is the wavelength of moving particles; atomic energy levels and line spectra.

How to study: This part is also taught domestically, but Cambridge questions often test written explanations, such as "why light below a certain frequency cannot produce photoelectrons regardless of its intensity." Practice explaining cause and effect in complete English sentences.

6. Nuclear Physics

Syllabus requirements: definition and use of mass defect and binding energy; plot the curve of binding energy per nucleon against nucleon number, and explain its relationship with nuclear fusion and fission; radioactive decay and half-life.

7. Medical Physics

This chapter is rarely taught in domestic high schools. The syllabus requirements are:

• Ultrasound: How piezoelectric transducers produce and detect ultrasound; how the reflection of ultrasound pulses at tissue boundaries is used for imaging; the attenuation formula I = I₀e^−μx;
• X-rays: Production of X-rays by electron bombardment of a metal target, calculating the minimum wavelength from the accelerating voltage; X-ray imaging and the concept of "contrast"; the same attenuation formula; the principle of CT (taking multiple images of the same cross-section from different angles and combining them);
• PET: Tracers emit positrons through β⁺ decay, and the positrons annihilate with electrons in the tissue, producing a pair of γ photons traveling in opposite directions.

8. Astrophysics and Cosmology

Syllabus requirements: standard candles; using Wien's displacement law to estimate the surface temperature of stars; using the Stefan-Boltzmann law L = 4πσr²T⁴; combining the two laws to estimate the radius of a star; Hubble's law v ≈ H₀d, and how it leads to the Big Bang theory.

How to study Medical Physics and Astrophysics: These two chapters don't have many formulas, but they are heavy on concepts and terminology. They are suitable for organizing into "principle—formula—written explanation" flashcards, and testing yourself with written questions from past papers.

4. Paper 5: How to Write the Experimental Planning Questions

Paper 5 consists of two questions, each worth 15 marks.

Question 1: Planning an Experiment (15 marks)

The question presents a problem and asks you to design an experiment to investigate it. The syllabus states that this question is not highly structured and should be answered with a diagram and a longer piece of text. The marks are divided into four areas:

The syllabus also specifically highlights two points:

• The apparatus must be practical: once set up as described, it should be able to collect data smoothly;
• The measuring instruments must be appropriate: they measure the correct physical quantities, and their precision is suitable for the experiment.

The syllabus specifically requires the ability to describe the use of instruments: using an oscilloscope to measure voltage, current, time, and frequency; using a light gate connected to a data logger to measure time, speed, and acceleration; and the use of other sensors (such as motion sensors) with data loggers.

Additionally, questions may be set in areas that are difficult to perform practically in a school lab (such as those involving radioactive materials), but they will not require theoretical or equipment knowledge beyond the syllabus; for out-of-syllabus content, the question will provide the necessary information.

A writing framework (empirical advice):

1. Write clearly in the first sentence: what the independent variable is, what the dependent variable is, and which variables are controlled;
2. Draw a large, clear diagram of the apparatus, labeling each instrument;
3. Write step-by-step: how to change the independent variable, what instruments to use to measure each quantity, and how to keep the control variables constant;
4. Write the analysis: the question usually gives the relationship between variables; explain what to plot against what, expect a straight line, and the criteria for the relationship to hold (e.g., "the line passes through the origin" or "the gradient equals...");
5. Additional details: repeat measurements to find an average, preliminary experiments to determine a suitable range, and specific precautions for the instruments;
6. Safety: write measures for the specific risks of this experiment, such as high voltage, high temperature, falling heavy objects, or lasers. Avoid vague statements like "pay attention to safety."

Question 2: Data Analysis and Uncertainties (15 marks)

The question provides an equation and a set of experimental data, asking you to determine a constant and estimate its uncertainty. The question is structured, but you need to judge what to do at each step. The marks cover data analysis, tables of results, graphing, conclusions, and handling uncertainties. The specific syllabus requirements:

• Linearizing equations: y = mx + c, y = axⁿ, y = ae^kx; plot y against x, lg y against lg x, and ln y against x respectively to find constants;
• Tables: Calculate derived quantities and fill in the table; use significant figures correctly; when taking logarithms, include the unit inside the logarithm, e.g., ln(d / cm), as the logarithm itself has no unit; the number of decimal places in the logarithm should match the number of significant figures in the original data—the syllabus example is L / cm = 76.5 (3 significant figures), so lg(L / cm) is written as 1.884 or 1.8837;
• Graphing: Draw error bars for each point (in both directions if necessary); draw the line of best fit and the worst acceptable line—the steepest or shallowest line passing through all error bars—using a dashed line or labeling it to distinguish it from the line of best fit;
• Conclusion: Determine the gradient and intercept, write the expressions equal to the gradient or intercept, and calculate the constants with correct units and significant figures;
• Uncertainties: Convert between absolute, fractional, and percentage uncertainties; write the absolute uncertainty next to each value in the table; calculate the uncertainty of derived quantities; uncertainty in gradient = gradient of line of best fit − gradient of worst acceptable line (same for intercept); express the final result as 'value ± uncertainty + unit'.

How to practice (empirical advice): The rules for this question are very fixed, and marks are mostly lost due to formatting details. After completing a question, check each item against the checklist above: whether logarithms include units, if decimal places are correct, if error bars are fully drawn, if the worst line passes through all error bars, and if the final answer includes uncertainty and units.

V. Study Schedule (Example)

Below are empirical suggestions based on a one-year A Level course schedule:

1. During the term: After finishing each chapter, complete the written explanation questions from past papers for that chapter; compare electric and gravitational fields, and various types of exponential decay;
2. Early practice for Paper 5: Do not wait until right before the exam. After finishing each electromagnetism or thermal physics topic, design an 'experimental design' question for yourself to answer; do one Q2 question every week and check the format against the checklist;
3. Medical physics and astrophysics: These two chapters are relatively independent with few formulas, making them suitable to be studied intensively over two to three weeks and turned into flashcards;
4. Two months before the exam: Practice full past papers for Paper 4 and Paper 5 under timed conditions, and review the AS content.

In Conclusion

In the A Level portion of A-Level Physics, what sets students apart is not the difficulty of calculations, but rather topics rarely taught in domestic schools (capacitance, Hall effect, medical physics, astrophysics) and the experimental conventions in Paper 5. Papers 4 and 5 together account for half of the total grade. By checking off the syllabus requirements one by one, you will be fully prepared to aim for an A*.

For the grade boundaries and required scores for an A*, see How to Achieve an A* in A-Level. The logarithms, exponentials, and graphing used in Papers 4 and 5 are closely related to math classes; students planning to apply for STEM majors can also check out How to Prepare for A-Level Further Mathematics. If you need A-Level Physics tutoring, feel free to chat with our teachers.

Verification note: This article was verified in September 2026 against the Cambridge International AS & A Level Physics 9702 syllabus (2025, 2026, and 2027 editions) published on the Cambridge Assessment International Education website: the duration, marks, weightings, and assessment objectives for Papers 4 and 5; the AS knowledge required for Paper 4; the content, marking schemes, skill requirements, instrument usage, and notes on possible out-of-syllabus areas for the two questions in Paper 5; as well as the topics and learning objectives for Chapters 12–25 in the A Level section, are all sourced from this syllabus. The 2028–2030 syllabus does not introduce major changes affecting teaching, as per the change notes from the new syllabus. This article does not cite grade boundaries: Cambridge grade boundaries vary each exam series, so please refer to the official grade boundary tables on the website. The study methods for each section, the writing framework for Paper 5, the study schedule, and the judgment on which topics are 'rarely taught in domestic schools' are our empirical suggestions.

References:

• Cambridge International: AS & A Level Physics (9702)