A-Level Physics Equations List by Topic with Rearrangements and Unit Checks

Overview

What you will get here is a practical A-Level physics formula list by topic, with a focus on exam use. Instead of presenting equations as a wall of symbols, this guide treats them as tools. For each area, the aim is to know four things: what the equation means, the common rearrangements, the expected SI units, and the warning signs that tell you you may be using it in the wrong context.

A strong equations routine matters because many A-Level physics errors are not really “physics knowledge” errors. They are setup errors: using frequency instead of period, mixing up current and charge, forgetting to convert cm to m, or substituting a wavelength in nm into an equation that expects metres. A quick unit check often finds these problems faster than re-reading the whole question.

Below is a compact but useful topic-based reference.

Mechanics

Velocity: v = s/t
Rearrangements: s = vt, t = s/v
Units: v in m s^-1, s in m, t in s

Acceleration: a = (v - u)/t
Rearrangements: v = u + at, u = v - at, t = (v - u)/a
Units: a in m s^-2

Newton’s second law: F = ma
Rearrangements: m = F/a, a = F/m
Units: F in N, m in kg, a in m s^-2
Unit check: 1 N = 1 kg m s^-2

Momentum: p = mv
Rearrangements: m = p/v, v = p/m
Units: p in kg m s^-1

Kinetic energy: E_k = 1/2 mv²
Rearrangements: m = 2E_k/v², v = √(2E_k/m)
Units: J, kg, m s^-1

Gravitational potential energy: ΔE_p = mgΔh
Rearrangements: m = ΔE_p/(gΔh), Δh = ΔE_p/(mg)
Units: J, kg, m s^-2, m

Power: P = E/t
Also: P = Fv for constant speed and force in the same direction
Units: W, J, s

Materials

Density: ρ = m/V
Rearrangements: m = ρV, V = m/ρ
Units: kg m^-3

Stress: stress = F/A
Units: Pa or N m^-2

Strain: strain = ΔL/L
Units: none

Young modulus: E = stress/strain
Units: Pa
Exam tip: strain has no unit, so Young modulus has the same unit as stress.

Waves

Wave speed: v = fλ
Rearrangements: f = v/λ, λ = v/f
Units: m s^-1, Hz, m

Period and frequency: f = 1/T
Rearrangements: T = 1/f
Units: Hz, s

Phase difference: fraction of cycle × 2π radians or × 360°
Exam tip: keep radians and degrees separate.

Electricity

Charge: Q = It
Rearrangements: I = Q/t, t = Q/I
Units: C, A, s

Potential difference: V = W/Q
Units: V, J, C

Resistance: R = V/I
Rearrangements: V = IR, I = V/R
Units: Ω

Power: P = IV
Also: P = I²R and P = V²/R
Exam tip: choose the version that uses the quantities already given to avoid unnecessary substitutions.

Resistivity: R = ρL/A
Rearrangements: ρ = RA/L, A = ρL/R
Units: ρ in Ω m, L in m, A in m²

Circular motion and fields

Centripetal acceleration: a = v²/r
Units: m s^-2

Centripetal force: F = mv²/r
Units: N

Gravitational field strength: g = F/m
Units: N kg^-1

Gravitational potential: V = W/m or energy per unit mass, depending on course wording
Exam note: distinguish clearly between potential and potential energy.

Further common A-Level areas

Capacitance: C = Q/V
Units: F

Exponential decay: N = N₀e^-λt
Units: λ in s^-1 if time is in seconds

Photon energy: E = hf
Also: E = hc/λ
Units: J, Hz, m

de Broglie wavelength: λ = h/p
Units: m, kg m s^-1

Ideal gas equation: pV = nRT
Units: p in Pa, V in m³, T in K

This list is not meant to replace your specification or formula sheet. It is a revision structure. For a broader study routine, see A-Level Physics Revision Using the “Second Opinion” Method.

Maintenance cycle

The most useful way to use an A-Level physics equations guide is on a regular cycle. This keeps formulas active in memory and makes exam technique smoother. A simple maintenance cycle works well across Year 12 and Year 13.

Weekly: choose one topic and do a ten-minute equation audit. Write each formula from memory, define every symbol, then check one unit conversion linked to that topic. For electricity, that might be mA to A. For waves, it might be nm to m. For mechanics, it might be km h^-1 to m s^-1.

Fortnightly: do mixed retrieval. Put mechanics, electricity, waves, and materials on the same page. The point is to spot which formulas you truly recognise by context and which ones you only remember when chapter headings are visible.

Monthly: add exam use. Take a short set of past-paper or exam-style questions and identify the required formula before solving. Many students can substitute values once the equation is given, but lose marks when they must select the equation independently. That selection skill improves only through repeated practice.

At the end of each topic: build a one-page topic sheet with four columns: equation, rearrangements, unit check, and common trap. Keep it short enough that you will actually revisit it.

Before mocks and final exams: switch from making notes to testing use. If you are still decorating a formula list the week before an exam, you are probably avoiding the harder but more useful task of applying it.

A sensible maintenance cycle also means checking what your board expects. Some courses provide formula support in certain assessments, while others expect more recall. Even if a formula is provided, you still need to interpret it, rearrange it, and combine it with another relationship. That is why equation fluency remains part of serious A-Level physics revision.

If you also teach or tutor, this cycle translates well into starter tasks, low-stakes quizzes, and hinge questions. Students benefit from seeing the same core equations recur in different contexts rather than in a single revision booklet they never reopen.

Signals that require updates

This article is built as a reference hub, so it should be revisited and refreshed. You do not need to wait for a full exam season to update your equations notes. Certain signals tell you that your list is no longer doing its job.

Signal 1: You remember the formula but not the conditions. For example, you know P = Fv but forget that it suits force and velocity in the same direction for constant speed problems. If context is missing, update the note beside the equation.

Signal 2: You keep making the same unit mistake. A repeated error is not random. It usually means your formula sheet lacks a clear unit warning. Add one. Next to pV = nRT, write “temperature in kelvin, not °C.” Next to resistivity, write “cross-sectional area in m².”

Signal 3: You can rearrange slowly but not under pressure. In that case, your list needs more than final formulas. It needs worked rearrangements. This is especially important for equations with squared terms, roots, and multiple variables.

Signal 4: Your specification coverage changes. As you move from AS content into full A-Level topics, your revision sheet should expand. Add fields, thermal physics, nuclear physics, turning points, electronics, or astrophysics sections as needed rather than keeping everything in a generic “miscellaneous” area.

Signal 5: Search intent shifts for you. Early in the course, you may search for “A-Level physics formula list.” Closer to exams, you are more likely to need “how to use formulas in exam questions” or “unit checks for A-Level physics equations.” Your own revision needs change over time, so your notes should change too.

Signal 6: You start combining equations. Stronger students often need a second version of the list that shows links between ideas. For example, using Q = It with E = QV gives E = IVt. Using p = mv with λ = h/p links particle momentum to wave behaviour. When your course reaches that stage, update your formula guide so it reflects the way real exam questions are structured.

For question practice built around this kind of linking, see A-Level Physics Revision: Electromagnetism Worked Problems with Exam-Style Solutions and How to Use Past Paper Questions as a Mini Scenario Analysis Exercise.

Common issues

The value of an equations list is often lost through a few predictable problems. If you fix these, the same list becomes much more useful.

1. Treating formulas as isolated facts.
Students often memorise V = IR, P = IV, and Q = It separately but do not notice how often electricity questions combine them. Try grouping connected equations on the page rather than alphabetically.

2. Ignoring symbol meaning.
The same letter can mean different things in different topics. V might mean volume or potential difference depending on context. E might mean energy or electric field strength in some notes. Write the quantity name beside the symbol every time until it becomes automatic.

3. Weak rearrangement habits.
A formula is only half known if you can use it in one form only. Practise rearranging before numbers are involved. Keep algebra separate from arithmetic.

4. Missing unit discipline.
This is one of the most common causes of lost marks. Convert first, then substitute. If you substitute first and convert later, mistakes multiply. Build a visible rule into your process: write values in SI units on a separate line before using the equation.

5. Over-reliance on triangle mnemonics.
Memory aids can help at the start, but they often fail once equations become more complex. At A-Level, understanding relationships is safer than relying on triangles that only work for a limited set of formulas.

6. Not checking whether the final answer is sensible.
A unit check tells you whether an answer is dimensionally plausible. A magnitude check tells you whether it is physically plausible. A wave speed faster than light in a simple medium, or a negative resistance from a straightforward circuit question, should make you stop and review your setup.

7. Making one giant sheet and never using it.
A long formula document can feel productive but be awkward in practice. It is often better to keep one master list and several smaller topic sheets for weekly revision.

8. Forgetting the practical connection.
Required practical physics is full of equations in action: gradient-based calculations, uncertainty discussions, resistivity measurements, and graph interpretation. Add a practical note next to relevant formulas. For example, next to R = ρL/A, note that resistivity can be found experimentally by measuring resistance, length, and diameter. This makes formulas easier to remember because they are tied to something you have done.

If your study time is spread between paper and screen, Physics Revision in Hybrid Learning: What Works Best for Memory, Speed, and Exam Performance? offers a useful framework for deciding what belongs in a notebook and what belongs in a digital revision system.

When to revisit

You should revisit this topic on purpose, not only when you feel stuck. The most effective times are predictable.

Revisit at the start of a new topic to see which older equations still matter. Mechanics appears again in fields and circular motion. Electricity ideas resurface in capacitance and practical work. Physics is cumulative, so your formula knowledge should be too.

Revisit after every marked test and update your list based on real errors. If a marker comments on unit conversion, significant figures, missing rearrangement steps, or misuse of a formula, that feedback should change your revision sheet the same day.

Revisit before required practical write-ups so that equations are linked to method, graph choice, and processing steps rather than memorised in isolation.

Revisit one month before mocks or final exams to trim your list. Remove clutter, highlight weak areas, and separate “know from memory” from “need practice applying.”

Revisit when search intent shifts in your own revision. If you stop asking “what is the equation?” and start asking “which equation should I choose here?” then move from reference mode into application mode with mixed questions and worked solutions.

To make this article useful as an ongoing hub, finish with a short action plan:

1. Create a master A-Level physics equations list by topic: mechanics, materials, waves, electricity, fields, nuclear, quantum, thermal, and any option topics you study.
2. For each equation, add one rearrangement you find difficult and one unit warning that has caught you before.
3. Test yourself weekly from memory, without headings.
4. Do at least one mixed set of physics exam questions each fortnight where your first task is choosing the equation, not just calculating the answer.
5. After every assessment, update the list using your mistakes rather than rewriting the whole page.
6. Keep a separate “unit traps” box covering common conversions such as cm to m, mm to m, g to kg, °C to K when needed, and nm to m.
7. In the final run-up to exams, use the list as a checklist, then spend most of your time on application, explanation, and multi-step problems.

If you are moving between GCSE and A-Level, it also helps to compare what has changed in style and difficulty. A useful starting point is GCSE Physics Equations List: What You Need to Memorise and How to Use Each Formula.

The best A-Level physics equations list is not the longest one. It is the one you can return to quickly, trust under pressure, and improve as your understanding grows. Keep it current, keep it practical, and let unit checks do more of the error-catching work for you.