Overview
When you first look at a Cambridge 9702 Physics mark scheme, the mix of letters and numbers like M1, A1, and B1 can seem like an indecipherable code. These abbreviations are the language examiners use to show precisely where each mark is awarded. Learning to speak this language is the key to understanding your mistakes and mastering the exam, allowing you to self-assess your work with accuracy and confidence.
The 'Big Three': M, A, and B Marks
Most marks in a 9702 paper fall into one of three categories. The most straightforward is the B mark (or 'independent' mark), often awarded for definitions, labelling a diagram correctly, or stating a known physical principle. A B1 mark is a standalone point that doesn't depend on a calculation. In contrast, M marks ('method' marks) are awarded for demonstrating the correct procedure in a calculation. This could be selecting the right equation from the data booklet or correctly substituting values into it. Finally, A marks ('accuracy' marks) are for the correct numerical answer. Crucially, an A1 mark is nearly always dependent on a preceding M1 mark being awarded; you cannot get marks for a correct answer that appears from incorrect or non-existent working. For a deeper dive into this, see our general guide on [how to read a Cambridge mark scheme](/blog/how-to-read-a-cambridge-mark-scheme).
ECF: Your Safety Net (Error Carried Forward)
For Cambridge syllabus 9702, eCF, or 'Error Carried Forward', is one of the most important concepts to understand when marking your own papers. It is a form of follow-through marking that prevents you from being penalised multiple times for a single early mistake. If you make a calculation error in part (a) of a question but then use that incorrect answer correctly in the method for part (b), ECF allows you to still earn the method marks for part (b). For example, if you calculate an incorrect value for acceleration but then correctly substitute it into `F=ma` to find a force, you will lose the accuracy mark but can still be awarded the method mark for applying Newton's second law correctly. This system is designed to credit your understanding of the physics, even if your arithmetic has let you down.
'oe' and Other Examiner Shorthand
Another common abbreviation you will encounter is oe, which stands for 'or equivalent'. This indicates that the examiner will accept alternative, scientifically correct ways of expressing the same point. For a definition, this might mean slightly different but equally valid wording. In a calculation, it could mean an answer expressed as a simplified fraction is just as acceptable as its decimal equivalent. Seeing 'oe' on a mark scheme is a reminder that physics is not just about memorising exact phrases from a textbook; it's about demonstrating a solid understanding of the concepts, and there is often more than one correct way to articulate that understanding.
The Unwritten Rules: Units and Significant Figures
For Cambridge syllabus 9702, while not always represented by a specific abbreviation like 'U' or 'SF', marks are frequently lost due to incorrect units or a clumsy use of significant figures. For many questions in Paper 2 and Paper 4, one of the final marks is implicitly tied to the correct unit. Forgetting to write 'N' for force or 'J' for energy is an easy way to drop a mark. Similarly, an 'sf penalty' is often applied for answers given to an inappropriate number of significant figures. As a rule of thumb, your final answer should be given to the same number of significant figures as the least precise piece of data used in the calculation, which for 9702 is usually two or three. Getting this right is a hallmark of a high-achieving student.
Putting It All Together: A Worked Example
For Cambridge syllabus 9702, a simple circuit contains a 6.0 V power supply connected to two resistors, R₁ (10 Ω) and R₂ (20 Ω), in series.
(a) Calculate the total resistance of the circuit. [1] (b) Calculate the current flowing from the supply. [2]
The official mark scheme might look like this:
- (a) R_total = R₁ + R₂ = 10 + 20 = 30 Ω [A1]
- (b) Use of I = V/R [M1] Current = 6.0 / 30 = 0.20 A [A1]
Now, imagine a student makes a mistake in part (a) and writes R_total = 10 Ω. They score 0/1 for part (a). In part (b), they calculate I = 6.0 / 10 = 0.60 A. Thanks to ECF, they would still be awarded the M1 mark for correctly selecting and applying Ohm's law, even though their final answer is wrong. They would not get the final A1 mark, scoring 1/2 for part (b). This demonstrates how partial credit is awarded.
Frequently asked questions
This section covers Frequently asked questions — ranked by what Cambridge examiners return to most often in past papers.
What's the difference between an M1 and a B1 mark?
A B1 mark is awarded for a correct, self-contained piece of information, like a definition or stating a law. It doesn't depend on other parts of the question. An M1 mark, however, is for a correct step within a longer process, typically a calculation. It rewards the method, not the knowledge itself.
If I get the final answer right by a fluke, do I get all the marks?
Almost certainly not. Examiners refer to this as a 'bald' correct answer. For any calculation worth more than one mark, you must show your working. Without the logical steps to back it up, you will not be awarded the M (method) marks, and you may even be denied the final A (accuracy) mark.
How many significant figures should I use in my answers?
Unless the question specifies otherwise, a good rule is to use the same number of significant figures as the least precise value given in the question data. In Cambridge A-Level Physics, this is typically two or three significant figures. It is good practice to keep more figures in your intermediate calculations to avoid premature rounding errors.