A-Level Physics Equations Guide: What to Memorise, What to Understand and How to Apply Them

Overview

If you search for A level physics equations, you will usually find a formula sheet, a specification list or a revision poster. Those can help, but they do not always answer the question students actually mean: what equations should I memorise, what should I understand, and how do I know which one to use?

The most useful way to revise equations is to stop seeing them as isolated facts. In A-level Physics, an equation is usually doing one or more of these jobs:

• linking two physical quantities in a simple proportional relationship
• summarising a process, such as energy transfer or motion
• helping you calculate an unknown from values in a question
• giving you a route into explanation, not just arithmetic

That is why a strong A level physics formula guide should include more than symbols. You also need to know:

• what each symbol means
• which units normally go with each quantity
• whether the equation is a definition, approximation or model
• what topic it belongs to
• what kinds of exam questions trigger it

A good rule is this: memorise the compact equations that appear again and again, understand the ones that can be rebuilt from definitions, and practise applying both in mixed questions.

For example, if you know that potential difference is energy transferred per unit charge, then V = W/Q is not just something to recall. It becomes a statement you can explain in words, use in rearranged form and connect to practical work. The same is true for definitions such as momentum, electric field strength, resistance and gravitational field strength.

Another useful distinction is between topic equations and bridge equations. Topic equations belong mostly to one area, such as wave speed or radioactive decay. Bridge equations connect several areas, such as conservation of energy, force relationships, density, power and inverse-square ideas. These bridge equations deserve extra revision time because they appear in many contexts.

If you want to build your wider revision in a sensible order, it helps to study equations alongside topic sequencing rather than in a random list. Our guide to A-Level Physics topics in order can help you decide what to revisit first.

Checklist by scenario

Use the checklist below depending on where you are in your revision. The aim is not to collect more notes. It is to make sure your equation knowledge is usable.

1. If you are starting a topic for the first time

Your priority is not full memorisation yet. Your priority is recognition and meaning.

• Write each new equation with words as well as symbols.
• Note the standard units beside each quantity.
• Ask what physical idea the equation expresses.
• Identify whether it is a definition, a law, or a derived relationship.
• Do one worked example and one explanation question using it.

At this stage, physics equations explained is more valuable than physics equations copied. If you cannot say what an equation means in plain English, you probably do not know it well enough.

2. If you are building your revision notes

This is where many students create pages that look tidy but are hard to revise from. Keep your equation notes lean.

• Group equations by topic: mechanics, materials, waves, electricity, fields, thermal physics, circular motion, quantum or nuclear, depending on your course.
• Highlight equations that come directly from definitions.
• Add one common exam use for each equation.
• Add one likely confusion, such as similar symbols or unit traps.
• Limit each topic to a one-page equation summary if possible.

For example, in mechanics, a compact page might include SUVAT links, force and momentum ideas, work done, power, efficiency and kinetic energy. What matters is not the length of the sheet but whether it helps you retrieve the right method quickly.

3. If you are asking what equations to memorise for A level physics

This is the question that usually appears close to mocks or final revision. The short answer is that you should know your own exam board requirements, but in practice you should prioritise equations in these categories:

• Definitions: quantities such as density, pressure, current, resistance, potential difference, power, momentum and field strength.
• Core mechanics relationships: force, acceleration, energy and motion equations used repeatedly across the course.
• Electricity and waves equations: these often appear in structured calculations and practical interpretation.
• Field and particle equations: particularly where understanding proportionality matters.
• Equations that support graph interpretation: decay, gradients, oscillations, resistivity-style practical relationships and inverse relationships.

A practical memory test is this: can you write the equation, define every symbol, give standard units and name one exam context where it appears? If not, keep it on your active memorisation list.

4. If you are revising for a closed-book class test or mock

Now the emphasis shifts from understanding to retrieval under pressure.

• Practise writing a full equation list from memory for one topic.
• Check symbols carefully, especially where one letter can mean different things in different topics.
• Practise rearranging equations without numbers first.
• Do short no-calculator identification drills: “Which equation fits this information?”
• Mix topics so you learn to choose, not just recall.

Students often think they have memorised equations because they can recognise them on a sheet. Recognition is much easier than recall. Your revision should test recall.

5. If you are preparing for calculation-heavy exam questions

For A level physics exam equations, application matters more than recitation. Use this checklist:

• Underline the quantity being asked for.
• List the values given and convert units before substituting.
• Choose the equation based on matching quantities, not on the topic title alone.
• Rearrange carefully before entering numbers if that reduces errors.
• Check the answer against common sense: too large, too small, wrong sign, wrong unit?

Many physics marks are dropped not because the student forgot the formula, but because they used centimetres with metres, milliseconds with seconds, or electronvolts with joules without converting.

6. If you struggle to know which equation to use

This is usually a selection problem, not a memory problem. Try this three-step method:

1. Name the topic and process. Is this motion, energy transfer, electric circuits, waves, fields or decay?
2. Identify the known and unknown quantities. Write the symbols down before searching for an equation.
3. Choose the shortest route. Pick the equation that uses the most given values with the fewest extra steps.

For example, if a question gives mass, speed and asks about energy, kinetic energy is the direct route. If it gives potential difference and current and asks about power, there may be more than one route, but one will usually be simpler and less error-prone.

7. If you are reviewing practicals and data questions

Equations are not just for numerical substitutions. In practical questions they often appear as tools for processing data and evaluating uncertainty.

• Check whether the equation predicts a straight-line graph after rearrangement.
• Know what gradient and intercept mean in common practical contexts.
• Match units on axes to the quantities in the formula.
• Look at whether the relationship is direct, inverse, squared or root-based.
• Practise explaining whether the data supports the model behind the equation.

This is one reason equations should be learned with graphs, not separately from them.

8. If you are close to the exam and short on time

Do not try to relearn the entire course from scratch. Prioritise reusable equation habits.

• Revise high-frequency definitions and core relationships first.
• Make a shortlist of your weakest ten equations.
• Do one mixed set of short calculations each day.
• Review unit conversions daily.
• Mark your work for method errors, not just final answers.

If your revision is very compressed, accuracy with familiar equations is worth more than vague exposure to every formula on the course.

What to double-check

Before you decide an equation is “learned”, check these five things. This is often where marks are saved.

Symbols and meanings

Some symbols change meaning depending on topic. Make sure you know what the symbol means in the specific equation you are using. A letter recognised out of context is not enough.

Units

Units are one of the best ways to check whether an equation choice is sensible. If the left-hand side and right-hand side units do not fit, something has gone wrong. Even where you are not asked to derive anything, unit awareness can protect you from basic mistakes.

Prefixes and conversions

Be careful with milli-, micro-, kilo- and mega-. A correct equation with an incorrect conversion still gives the wrong answer. Build a habit of converting values before substitution unless there is a strong reason not to.

Rearrangement

Algebra errors can turn an easy question into a lost method mark. Practise rearranging common equations without numbers. If you only ever substitute immediately, weak algebra stays hidden until the exam.

Physical sense

Your final answer should fit the situation. A speed greater than an obvious maximum, a negative resistance, or a field value that is wildly inconsistent with the setup should make you pause and check your steps.

Common mistakes

Most equation problems come from a small set of repeat errors. If you can reduce these, your marks often rise quickly.

• Memorising form without meaning. This makes it hard to select the right equation in unfamiliar contexts.
• Forgetting definitions. Definition-based equations are often the most useful because they support explanation as well as calculation.
• Mixing symbols from different topics. Similar letters can lead to avoidable confusion.
• Skipping unit conversion. This is especially common with centimetres, grams, milliseconds and micro-units.
• Using every given number. Not every number in a question belongs in the same equation.
• Choosing by memory of the chapter, not by the quantities involved. Exams often blend topics.
• Not checking whether an equation is the full route. Sometimes you need a two-step method rather than forcing one formula to do everything.
• Ignoring graph forms. Equations often appear in disguised form through gradients, intercepts and transformed axes.

A helpful correction strategy is to keep an “equation error log”. After each past paper or topic test, write down:

• the equation you should have used
• the mistake you made
• the trigger that should have alerted you
• one quick practice question to repeat later

This turns mistakes into a revision resource instead of letting them repeat. If you want a broader method for using exam papers effectively, our GCSE-focused guide on how to use science past papers still offers a useful framework for reviewing calculation errors and timing.

When to revisit

Equation revision works best when you revisit it at predictable points, not only when panic sets in. Use this article as a checklist at these moments:

• At the start of a new topic: build understanding before memorisation.
• At the end of each half term: rewrite a topic equation sheet from memory and fill gaps.
• Before mocks: test recall, rearrangement and unit conversions under timed conditions.
• After each past paper: update your error log and identify weak equations.
• During final revision: shift from collecting formulas to applying them in mixed questions.

If your school changes resources, if your teacher starts using a different booklet, or if you move from single-topic homework to synoptic paper practice, revisit your equation strategy. The equations themselves may not change much, but the way you need to use them often does.

For a practical next step, try this 20-minute routine:

1. Choose one topic.
2. Write all key equations you remember without notes.
3. Add the words and units for each symbol.
4. Do three short questions: one direct substitution, one rearrangement, one explanation.
5. Mark mistakes and add them to your equation error log.

Repeat that across the course and your equation knowledge becomes active rather than passive. That is the real goal of an A level physics formula guide: not to give you a longer list, but to help you think more clearly when a question is in front of you.

If you are planning the rest of your revision, pair this checklist with a structured topic order using our guide to A-Level Physics topics in order. Good equation revision is most effective when it follows a clear sequence and gets revisited before each new round of tests, mocks and exam papers.