The three most common mistakes when marking GCSE Physics papers

I’ve marked thousands of GCSE students’ exam questions over the years. Here are some of those common mistakes I see year after year.

1. Command words

If the question asks you to “explain”, you must give physics reasons. If it says “describe” or “state“, don’t waste your time. So often students miss the point of a question because they waste time giving an excellent physics explanation to a one-mark “describe” question.

Worse is when a student gives a beautiful description as an answer to an “explain” question, and so misses all (or nearly all) of the points from the mark scheme.

Usually physics explanations boil down to one of two types: what’s the energy doing, or what is going on with the forces. With only two things to remember, physics ought to be the easiest subject!

2. Unit prefixes

Many students have dropped a mark here or there because they didn’t spot the milli or micro on a unit, or they used grams not kilograms in a density question. It’s an easy mistake to make, but those unit prefix marks will add up.

Now formula sheets are given to students, the examiners have to find new ways to con students out of marks. Slipping a unit prefix in here and there is an easy way to get a spread of results.I

If the question said, “how many grams in 2.4kg”, students would likely get it right, no problem. But because it’s buried amongst a calculation, it easily gets missed.

Each time you write a number, look out for the prefix. Check and double check.

3. Vagueness in answers

Some questions are not obviously multiple choice, and yet the answer actually comes down to a 50/50 choice between two options. You’d think that means there’s no way less than half of the students would get it right, but alas the question is hidden behind a vague word in the question. Look out for words like ‘change‘.

For example, “Explain how inserting control rods deeper in the reactor core changes the power output of the reactor.” Many students tried to give a correct explanation in terms of the rate of neutron absorption, but they failed to say whether the controls being deeper would increase or decrease it.

Another example, “Describe the factors that increase the braking distance of a car.” Here there is no word change, but many students give vague answers anyway, such as “condition of the tyres” rather than saying “poor condition of the tyres.”

Bonus mistake: rewriting the question

Four things are in limited supply during examinations: the ink in your pen, the space on the paper, the time you have left, and your ability to maintain focus. Students who waffle by rewriting the question without actually saying anything waste all four.

For example, if the question says, “Explain why pumping more air into the tyre causes the internal energy to increase”, don’t start your answer with “pumping more air into the tyre causes the energy to increase because…”

Remember, any answer that can start with the word “because” is perfectly good with the word “because” omitted. I understand why this happens; it is encouraged and rewarded in other subjects. Physics is different, and waffle rarely adds anything of value.