The Complete IGCSE Physics 0625 Equations List

Use this resource for The Complete IGCSE Physics 0625 Equations List alongside the current syllabus and original practice. It is designed to support active recall, marking and correction rather than passive rereading.

The tier label applies to the equation itself. A page can contain both Core and Supplement material, so do not infer the tier from the page title alone.

Important corrections from older formula lists

The current list:

• includes the Core Celsius-to-kelvin relationship
• marks acceleration, momentum, kinetic energy and gravitational potential energy equations as Supplement
• marks the two efficiency equations as Supplement
• marks electric current as charge per unit time as Supplement
• marks orbital speed as Supplement
• keeps the transformer voltage-turns ratio as Core
• excludes the obsolete specific latent heat equation
• excludes a linear lens magnification equation that is not listed in the current syllabus

How should you learn the equations?

Use active recall rather than repeatedly reading the table.

1. Cover the symbols column.
2. Write the equation from the quantity names.
3. Rearrange it for every variable.
4. State the unit of each quantity.
5. Complete one original question using the equation.
6. Record whether the mistake was recall, algebra, unit conversion or Physics interpretation.

The goal is not only to remember a formula. It is to recognise when it applies and when it does not.

Topic 1: Motion, Forces and Energy

Core equations

Quantity relationship	Equation	Common units
speed = distance travelled / time	$v = \dfrac{s}{t}$	m/s, m, s
average speed = total distance / total time	$\text{average speed} = \dfrac{\text{total distance}}{\text{total time}}$	m/s, m, s
gravitational field strength = weight / mass	$g = \dfrac{W}{m}$, so $W = mg$	N/kg, N, kg
density = mass / volume	$\rho = \dfrac{m}{V}$	kg/m³, kg, m³
moment = force × perpendicular distance from pivot	$\text{moment} = Fd$	N m, N, m
work done = force × distance moved in the force direction	$W = Fd = \Delta E$	J, N, m
power = work done / time	$P = \dfrac{W}{t}$	W, J, s
power = energy transferred / time	$P = \dfrac{\Delta E}{t}$	W, J, s
pressure = force / area	$p = \dfrac{F}{A}$	Pa, N, m²

Core notes

• Speed can also be obtained from the gradient of a straight section of a distance-time graph.
• Distance can be obtained from the area under a speed-time graph for the situations specified in the syllabus.
• Near Earth’s surface, $g$ is approximately $9.8\text{ m/s}^2$, equivalent to approximately $9.8\text{ N/kg}$ as a gravitational field strength.
• The symbol $W$ can represent weight in $W = mg$ and work in $W = Fd$. Use the context and units.

Supplement equations

Quantity relationship	Equation	Common units
acceleration = change in velocity / time taken	$a = \dfrac{\Delta v}{\Delta t}$	m/s², m/s, s
spring constant = force / extension	$k = \dfrac{F}{x}$	N/m, N, m
resultant force = mass × acceleration	$F = ma$	N, kg, m/s²
momentum = mass × velocity	$p = mv$	kg m/s, kg, m/s
impulse = force × time = change in momentum	$F\Delta t = \Delta(mv)$	N s or kg m/s
resultant force = change in momentum / time	$F = \dfrac{\Delta p}{\Delta t}$	N
kinetic energy	$E_k = \dfrac{1}{2}mv^2$	J, kg, m/s
change in gravitational potential energy	$\Delta E_p = mg\Delta h$	J, kg, N/kg, m
percentage efficiency from energy	$\text{efficiency} = \dfrac{\text{useful energy output}}{\text{total energy input}} \times 100\%$	%
percentage efficiency from power	$\text{efficiency} = \dfrac{\text{useful power output}}{\text{total power input}} \times 100\%$	%
change in liquid pressure	$\Delta p = \rho g\Delta h$	Pa, kg/m³, N/kg, m

Supplement notes

• The syllabus explicitly states that $F = mv^2/r$ is not required for circular motion.
• Efficiency cannot exceed 100% in the model used here.
• For liquid pressure, use the change in vertical depth, not the distance travelled along a sloping container.

Topic 2: Thermal Physics

Core equation

Quantity relationship	Equation	Units
kelvin temperature = Celsius temperature + 273	$T\text{ (K)} = \theta\text{ (°C)} + 273$	K and °C

A temperature interval has the same numerical size in kelvin and degrees Celsius. For example, a rise of 10 °C is a rise of 10 K.

Supplement equations

Quantity relationship	Equation	Common units
pressure × volume is constant for a fixed mass of gas at constant temperature	$pV = \text{constant}$ or $p_1V_1 = p_2V_2$	matching pressure and volume units
specific heat capacity = energy transferred / (mass × temperature change)	$c = \dfrac{\Delta E}{m\Delta\theta}$	J/(kg °C), J, kg, °C

Thermal warning

The 2026 to 2028 syllabus does not list:

$E = mL$

or

$L = \frac{E}{m}$

as current specific latent heat requirements. Do not add them to a current 0625 formula sheet. Melting, boiling, condensation, solidification and evaporation remain examinable qualitatively.

Topic 3: Waves

Core equations and relationships

Quantity relationship	Equation	Common units
wave speed = frequency × wavelength	$v = f\lambda$	m/s, Hz, m
angle of incidence = angle of reflection	$i = r$	degrees

The value for the speed of electromagnetic waves in a vacuum is approximately:

$3.0 \times 10^8\text{ m/s}$

This is a physical value rather than a separate formula.

Supplement equations

Quantity relationship	Equation	Units
refractive index from angles	$n = \dfrac{\sin i}{\sin r}$	no unit
refractive index from critical angle	$n = \dfrac{1}{\sin c}$	no unit

Waves warning

The current syllabus does not list a linear magnification equation such as $M = h_i/h_o$. Students still need to construct the required ray diagrams and describe image characteristics.

Topic 4: Electricity and Magnetism

Core equations

Quantity relationship	Equation	Common units
resistance = potential difference / current	$R = \dfrac{V}{I}$	Ω, V, A
electrical power = current × potential difference	$P = IV$	W, A, V
electrical energy = current × potential difference × time	$E = IVt$	J, A, V, s
combined resistance in series	$R_{\text{total}} = R_1 + R_2 + \cdots$	Ω
transformer voltage ratio = turns ratio	$\dfrac{V_p}{V_s} = \dfrac{N_p}{N_s}$	V and number of turns

The kilowatt-hour is an energy unit used in appliance-cost calculations:

$\text{cost} = \text{energy used in kWh} \times \text{price per kWh}$

Supplement equations and relationships

Quantity relationship	Equation	Common units
current = charge / time	$I = \dfrac{Q}{t}$, so $Q = It$	A, C, s
e.m.f. = work done by source / charge	$E = \dfrac{W}{Q}$	V, J, C
potential difference = work done / charge	$V = \dfrac{W}{Q}$	V, J, C
resistance is proportional to length	$R \propto l$	relationship only
resistance is inversely proportional to cross-sectional area	$R \propto \dfrac{1}{A}$	relationship only
combined resistance of two resistors in parallel	$\dfrac{1}{R} = \dfrac{1}{R_1} + \dfrac{1}{R_2}$	Ω
potential-divider ratio for two resistors	$\dfrac{R_1}{R_2} = \dfrac{V_1}{V_2}$	no unit for the ratio
ideal-transformer input power = output power	$I_pV_p = I_sV_s$	W from A × V
power dissipated in a cable	$P = I^2R$	W, A, Ω

Circuit relationships without a separate formula

Supplement candidates also calculate using these relationships:

• total current entering a junction equals total current leaving
• total potential difference across series components equals the sum of the individual potential differences
• potential difference across parallel branches is the same

These relationships should be applied to the actual circuit rather than memorised as an isolated string of symbols.

Topic 5: Nuclear Physics

Nuclear Physics uses conservation relationships rather than a long formula list.

Nuclide notation

${}^{A}_{Z}X$

where:

• $A$ is nucleon number, equal to protons plus neutrons
• $Z$ is proton number
• number of neutrons = $A - Z$

In decay, fission and fusion equations, total nucleon number and total proton number must be conserved.

Half-life

After each half-life, the number of undecayed nuclei or the corrected activity halves:

$N \rightarrow \frac{N}{2} \rightarrow \frac{N}{4} \rightarrow \frac{N}{8}$

Core calculations use the syllabus conditions specified for Core. Supplement questions can include data from which background radiation has not already been subtracted, so remove the background count before analysing the source count where required.

Topic 6: Space Physics

Supplement equations and numerical relationships

Quantity relationship	Equation	Common units
average orbital speed	$v = \dfrac{2\pi r}{T}$	m/s, m, s
Hubble constant = recession speed / distance	$H_0 = \dfrac{v}{d}$	s⁻¹, m/s, m
age estimate of the Universe	$\dfrac{d}{v} = \dfrac{1}{H_0}$	s

The syllabus also gives:

$1\text{ light-year} = 9.5 \times 10^{15}\text{ m}$

and the current syllabus estimate:

$H_0 = 2.2 \times 10^{-18}\text{ s}^{-1}$

Use the value supplied by the question or current syllabus material.

A reliable calculation method

For each numerical question:

1. identify the required quantity
2. write the appropriate equation
3. convert units before substitution
4. rearrange clearly
5. substitute with visible working
6. calculate
7. round appropriately
8. write the unit
9. check whether the answer is physically plausible

A memorised equation is only useful when the quantities, conditions and tier are also understood. Pair this list with the calculation-method guide and the relevant topic questions rather than learning the table in isolation.