Cambridge IGCSE Physics (0625) equations

The Cambridge IGCSE Physics 0625 syllabus marks every equation below as "recall and use", so you need all of them from memory. Core students need the Core list. Extended students, who sit Papers 2 and 4, need the Core list and the Supplement list.

The last column gives the syllabus section, so you can find each equation in the official syllabus. The equations are as written in the syllabus for exams in 2026, 2027 and 2028.

Practise with marked questions

Core equations (all students)

Cambridge IGCSE Physics Core equations
In words	Equation	Symbols and units	Syllabus
speed = distance travelled ÷ time	$v = \dfrac{s}{t}$	$v$ m/s; $s$ m; $t$ s	1.2
average speed = total distance travelled ÷ total time taken	No symbol form	m/s	1.2
gravitational field strength = weight ÷ mass	$g = \dfrac{W}{m}$	$g$ N/kg; $W$ N; $m$ kg	1.3
density = mass ÷ volume	$\rho = \dfrac{m}{V}$	$\rho$ kg/m³ or g/cm³; $m$ kg; $V$ m³	1.4
moment = force × perpendicular distance from the pivot	No symbol form	moment N m	1.5.2
work done = force × distance = energy transferred	$W = Fd = \Delta E$	$W$ J; $F$ N; $d$ m	1.7.2
power = work done ÷ time, and power = energy transferred ÷ time	$P = \dfrac{W}{t} \quad P = \dfrac{\Delta E}{t}$	$P$ W; $W, E$ J; $t$ s	1.7.4
pressure = force ÷ area	$p = \dfrac{F}{A}$	$p$ Pa; $F$ N; $A$ m²	1.8
temperature in kelvin = temperature in °C + 273	$T\,(\text{K}) = \theta\,({}^\circ\text{C}) + 273$	K and °C	2.1.3
wave speed = frequency × wavelength	$v = f\lambda$	$v$ m/s; $f$ Hz; $\lambda$ m	3.1
angle of incidence = angle of reflection	$i = r$	degrees	3.2.1
resistance = potential difference ÷ current	$R = \dfrac{V}{I}$	$R$ Ω; $V$ V; $I$ A	4.2.4
electrical power = current × potential difference	$P = IV$	$P$ W; $I$ A; $V$ V	4.2.5
electrical energy = current × potential difference × time	$E = IVt$	$E$ J; $I$ A; $V$ V; $t$ s	4.2.5
combined resistance of resistors in series (the syllabus asks you to calculate it)	$R = R_1 + R_2 + \dots$	$R$ Ω	4.3.2
transformer: p.d. ratio = turns ratio	$\dfrac{V_p}{V_s} = \dfrac{N_p}{N_s}$	$V$ V	4.5.6

Supplement equations (Extended only)

Cambridge IGCSE Physics Supplement equations
In words	Equation	Symbols and units	Syllabus
acceleration = change in velocity ÷ time taken	$a = \dfrac{\Delta v}{\Delta t}$	$a$ m/s²; $v$ m/s; $t$ s	1.2
spring constant = force ÷ extension	$k = \dfrac{F}{x}$	$k$ N/m; $F$ N; $x$ m	1.5.1
resultant force = mass × acceleration	$F = ma$	$F$ N; $m$ kg; $a$ m/s²	1.5.1
momentum = mass × velocity	$p = mv$	$p$ kg m/s; $m$ kg; $v$ m/s	1.6
impulse = force × time = change in momentum	$\text{impulse} = F\Delta t = \Delta(mv)$	N s (equal to kg m/s)	1.6
resultant force = change in momentum ÷ time	$F = \dfrac{\Delta p}{\Delta t}$	$F$ N; $p$ kg m/s; $t$ s	1.6
kinetic energy	$E_k = \tfrac{1}{2}mv^2$	$E_k$ J; $m$ kg; $v$ m/s	1.7.1
change in gravitational potential energy	$\Delta E_p = mg\Delta h$	$E_p$ J; $m$ kg; $g$ N/kg; $h$ m	1.7.1
efficiency = useful energy output ÷ total energy input (× 100%), or useful power output ÷ total power input (× 100%)	No symbol form	No unit (a ratio or a percentage)	1.7.3
change in pressure beneath the surface of a liquid	$\Delta p = \rho g\Delta h$	$p$ Pa; $\rho$ kg/m³; $g$ N/kg; $h$ m	1.8
for a fixed mass of gas at constant temperature	$pV = \text{constant}$	$p$ Pa; $V$ m³	2.1.3
specific heat capacity = energy ÷ (mass × temperature change)	$c = \dfrac{\Delta E}{m\Delta\theta}$	$c$ J/(kg °C); $E$ J; $m$ kg; $\theta$ °C	2.2.2
refractive index	$n = \dfrac{\sin i}{\sin r}$	No unit	3.2.2
refractive index and the critical angle	$n = \dfrac{1}{\sin c}$	No unit	3.2.2
current = charge ÷ time	$I = \dfrac{Q}{t}$	$I$ A; $Q$ C; $t$ s	4.2.2
e.m.f. = work done ÷ charge, and p.d. = work done ÷ charge	$E = \dfrac{W}{Q} \quad V = \dfrac{W}{Q}$	$E, V$ V; $W$ J; $Q$ C	4.2.3
combined resistance of two resistors in parallel (the syllabus asks you to calculate it)	$\dfrac{1}{R} = \dfrac{1}{R_1} + \dfrac{1}{R_2}$	$R$ Ω	4.3.2
potential divider with two resistors	$\dfrac{R_1}{R_2} = \dfrac{V_1}{V_2}$	$R$ Ω; $V$ V	4.3.3
transformer at 100% efficiency	$I_pV_p = I_sV_s$	$I$ A; $V$ V	4.5.6
power lost in cables	$P = I^2R$	$P$ W; $I$ A; $R$ Ω	4.5.6
average orbital speed	$v = \dfrac{2\pi r}{T}$	$v$ m/s; $r$ m; $T$ s	6.1.1
Hubble constant = recession speed ÷ distance	$H_0 = \dfrac{v}{d}$	$H_0$ per second; $v$ m/s; $d$ m	6.2.3
estimate for the age of the Universe	$\dfrac{d}{v} = \dfrac{1}{H_0}$	s	6.2.3

Values the syllabus asks you to know

The acceleration of free fall near the Earth’s surface is about 9.8 m/s². The speed of electromagnetic waves in a vacuum is $3.0 \times 10^8$ m/s (Supplement). The speed of sound in air is about 330 to 350 m/s. One light-year is $9.5 \times 10^{15}$ m (Supplement). The current estimate for $H_0$ is $2.2 \times 10^{-18}$ per second (Supplement).

Practise these with marked questions

Exam-style questions for every topic, free to read. Answer them online and Exaim marks each answer against the mark scheme, showing which marks you earned.

Cambridge IGCSE Physics (0625) equations

Core equations (all students)

Supplement equations (Extended only)

Values the syllabus asks you to know

Practise these with marked questions

More formula sheets