Equations to Memorise

In the Edexcel GCSE Combined Science exam (1SC0), some equations are provided on an equations sheet and some are not. The equations listed in this lesson are those you must recall from memory — they will not be on the sheet. Organise your revision around learning these by heart.

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How Equations Are Tested

• If an equation is on the recall list, the question may say "Use the correct equation from your knowledge" or simply "Calculate..." without giving you the formula.
• If an equation is on the sheet, the question may say "Use the equation from the Physics Equations Sheet."
• Either way, you must write the equation as the first line of your working.

Exam Tip: Learning all recall equations means you never waste exam time searching the equation sheet for something that is not there.

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Biology Equations to Recall

Biology has fewer mathematical equations, but you must recall these key relationships:

Equation	Variables	Notes
magnification = image size ÷ actual size	magnification (×), image size (mm or µm), actual size (mm or µm)	Used for microscopy calculations
BMI = mass ÷ height²	BMI (kg/m²), mass (kg), height (m)	Body Mass Index

Word Equations for Key Reactions

You must also recall these word equations:

Process	Word equation
Aerobic respiration	glucose + oxygen → carbon dioxide + water (+ energy transferred)
Anaerobic respiration (animals)	glucose → lactic acid (+ energy transferred)
Anaerobic respiration (yeast / plants)	glucose → ethanol + carbon dioxide (+ energy transferred)
Photosynthesis	carbon dioxide + water → glucose + oxygen (light energy required)

Exam Tip: You must know the difference between the animal and yeast versions of anaerobic respiration. They produce different products.

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Chemistry Equations to Recall

Equation	Variables	Notes
relative formula mass (M_r) = sum of A_r values	A_r = relative atomic mass	Not a formula you substitute into, but a calculation method you must know
moles = mass ÷ M_r	moles (mol), mass (g), M_r (g/mol)	The key moles equation
concentration = moles ÷ volume	concentration (mol/dm³), moles (mol), volume (dm³)	Also written as c = n/V
concentration (g/dm³) = mass ÷ volume	concentration (g/dm³), mass (g), volume (dm³)	Alternative concentration form
atom economy = (M_r of desired product ÷ sum of M_r of all products) × 100	All M_r values	Percentage value
percentage yield = (actual yield ÷ theoretical yield) × 100	Both yields in same unit	Percentage value
mean rate of reaction = quantity of reactant used ÷ time	or quantity of product formed ÷ time	Various units depending on quantity measured

Balancing Symbol Equations

You do not receive equations to balance — you must be able to:

1. Write a symbol equation from a word equation.
2. Balance the equation by adjusting coefficients.
3. Include state symbols (s), (l), (g), (aq) if asked.

Exam Tip: When balancing, change coefficients only — never change the subscript numbers within a formula.

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Physics Equations to Recall

Physics has the longest recall list. These are the equations you will not find on the equation sheet.

Equation	Variables and units
v = f × λ	wave speed (m/s), frequency (Hz), wavelength (m)
v = s ÷ t	speed (m/s), distance (m), time (s)
a = Δv ÷ t	acceleration (m/s²), change in velocity (m/s), time (s)
F = m × a	force (N), mass (kg), acceleration (m/s²)
W = F × d	work done (J), force (N), distance (m) — in direction of force
P = E ÷ t	power (W), energy (J), time (s)
P = W ÷ t	power (W), work done (J), time (s)
Ek = ½ × m × v²	kinetic energy (J), mass (kg), velocity (m/s)
Ep = m × g × h	gravitational potential energy (J), mass (kg), g (N/kg), height (m)
efficiency = useful output ÷ total input × 100	energy or power values; percentage
Q = I × t	charge (C), current (A), time (s)
V = I × R	potential difference (V), current (A), resistance (Ω)
P = I × V	power (W), current (A), potential difference (V)
E = Q × V	energy transferred (J), charge (C), potential difference (V)
density = mass ÷ volume	density (kg/m³), mass (kg), volume (m³)
weight = mass × g	weight (N), mass (kg), gravitational field strength (N/kg)
momentum = mass × velocity	momentum (kg m/s), mass (kg), velocity (m/s)

Exam Tip: A good technique is to write all the recall equations on flashcards — equation on the front, a worked example on the back. Test yourself daily in the weeks before the exam.

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Mnemonics and Memory Aids

Equation	Triangle / Mnemonic
v = f × λ	"Very Fast Lamborghini" — speed = frequency × wavelength
V = I × R	"Volts = Iguanas × Running" or use the VIR triangle
P = I × V	"Power = I × Volts" — PIV triangle
Ek = ½mv²	"Half my velocity squared" — note the ½ and the v²
F = m × a	"Force Makes Acceleration"

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How to Practise

1. Cover and write — cover the equation column, write each equation from memory, then check.
2. Flashcard drill — shuffle and test randomly.
3. Apply — for each equation, make up a simple calculation and solve it.
4. Past papers — identify which equation each calculation question requires before solving.

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Summary