CCEA GCSE Physics

Energy Stores

Store	Description	Example
Kinetic	Energy of a moving object	Running person
Gravitational PE	Energy due to height in a gravitational field	Book on a shelf
Elastic PE	Energy stored in a stretched/compressed object	Stretched spring
Thermal	Energy related to temperature of an object	Hot water
Chemical	Energy stored in chemical bonds	Food, fuels, batteries
Nuclear	Energy stored in the nucleus of atoms	Uranium, the Sun
Electrostatic	Energy due to separated charges	Charged balloon
Magnetic	Energy due to magnetic fields	Fridge magnet

Energy Transfer Pathways

• Mechanically (by a force doing work)
• Electrically (by current in a circuit)
• By heating (conduction, convection, radiation)
• By radiation (light, sound, EM waves)

Energy cannot be created or destroyed, only transferred from one store to another.

The total energy in a closed system is always conserved. Energy is often "wasted" as thermal energy (heat) transferred to the surroundings.

Power is measured in watts (W). 1 W = 1 J/s.

Also: Efficiency = (useful output power / total input power) x 100%

Efficiency can never exceed 100%. Wasted energy is usually thermal energy lost to surroundings.

Where: E = energy (J), m = mass (kg), c = specific heat capacity (J/kg°C), ΔT = temperature change (°C)

Specific heat capacity is the energy needed to raise the temperature of 1 kg of a substance by 1°C.

• Water: c = 4200 J/kg°C (high -- good coolant)
• Aluminium: c = 900 J/kg°C
• Copper: c = 390 J/kg°C

Conduction

Transfer of thermal energy through a material by vibrating particles passing energy to neighbours. Works best in solids (especially metals, due to free electrons).

Convection

Transfer of thermal energy by the movement of a heated fluid (liquid or gas). Hot fluid rises (less dense), cool fluid sinks, creating a convection current. Does NOT work in solids or a vacuum.

Radiation (Infrared)

Transfer of energy by electromagnetic waves (infrared). Works through a vacuum. All objects emit and absorb IR radiation.

• Dark, matt surfaces are good absorbers and emitters.
• Light, shiny surfaces are good reflectors (poor absorbers).

Insulation

Reduces heat loss: cavity wall insulation (traps air, reduces convection), loft insulation, double glazing, draught-proofing.

Non-Renewable

Resource	Advantages	Disadvantages
Coal, oil, gas	Reliable, high output, available on demand	CO&sub2; emissions, finite, pollution
Nuclear	No CO&sub2; in operation, very high output	Radioactive waste, decommissioning cost, risk of accident

Renewable

Resource	Advantages	Disadvantages
Solar	No pollution, free energy source	Intermittent, expensive panels, large area needed
Wind	No pollution, free energy source	Intermittent, visual/noise pollution, expensive
Hydroelectric	Reliable, instant response, no pollution	Flooding habitats, expensive to build, limited sites
Tidal	Predictable, reliable	Few suitable sites, expensive, environmental impact
Geothermal	Reliable, low running costs	Few suitable sites, high setup cost
Biomass	Carbon neutral (in theory), uses waste	CO&sub2; when burned, land use, transport costs

• Amplitude -- maximum displacement from the rest position (metres)
• Wavelength (λ) -- distance from one point on a wave to the same point on the next wave (metres)
• Frequency (f) -- number of waves passing a point per second (Hz)
• Period (T) -- time for one complete wave: T = 1/f

Transverse Waves

Oscillations are perpendicular (at right angles) to the direction of energy transfer.

Examples: light, water waves, EM waves, S-waves (seismic)

Longitudinal Waves

Oscillations are parallel to the direction of energy transfer. They consist of compressions and rarefactions.

Examples: sound waves, P-waves (seismic), ultrasound

Sound is a longitudinal wave caused by vibrations. It needs a medium to travel through (cannot travel through a vacuum).

Speed of Sound

• Solids: fastest (~5000 m/s in steel)
• Liquids: medium (~1500 m/s in water)
• Gases: slowest (~340 m/s in air)

Echoes

Sound reflects off hard surfaces. Used to calculate distances (e.g., sonar).

Ultrasound

Sound above 20,000 Hz (above human hearing range). Uses: prenatal scanning, cleaning jewellery, industrial flaw detection, sonar.

All EM waves travel at the speed of light (3 x 10&sup8; m/s) in a vacuum, are transverse, and transfer energy.

Type	Use	Danger
Radio	TV, radio broadcasts, communications	Generally safe
Microwave	Cooking, mobile phones, satellite	Can heat body tissue
Infrared	Heating, remote controls, thermal cameras	Burns skin
Visible light	Seeing, photography, fibre optics	Can damage eyes
Ultraviolet	Sterilisation, fluorescence, tanning	Skin cancer, eye damage
X-ray	Medical imaging, airport security	Cell damage, cancer
Gamma	Cancer treatment, sterilisation	Cell damage, cancer

Order (increasing frequency / decreasing wavelength): R M I V U X G

Law of Reflection

Angle of incidence = Angle of reflection

Both angles are measured from the normal (the line perpendicular to the surface at the point of incidence).

Plane Mirrors

• Image is virtual, upright, same size, laterally inverted
• Image is the same distance behind the mirror as the object is in front

Refraction is the change in direction of a wave as it passes from one medium to another, caused by a change in speed.

• Light entering a denser medium (air to glass): slows down, bends towards the normal
• Light entering a less dense medium (glass to air): speeds up, bends away from the normal

Total Internal Reflection (TIR)

Occurs when light travels from a denser to a less dense medium at an angle greater than the critical angle. All light is reflected back inside.

Uses: optical fibres (telecommunications, endoscopes), reflectors, prisms in binoculars.

Converging (Convex) Lens

Thicker in the middle. Brings parallel light to a focus (focal point, F).

• Object beyond 2F: real, inverted, diminished image
• Object at 2F: real, inverted, same size
• Object between F and 2F: real, inverted, magnified
• Object inside F: virtual, upright, magnified (magnifying glass)

Diverging (Concave) Lens

Thinner in the middle. Spreads light out. Always produces a virtual, upright, diminished image.

White light is made up of all colours of the visible spectrum.

Colour of Objects

• A red object reflects red light and absorbs all other colours
• A white object reflects all colours
• A black object absorbs all colours

Colour Filters

A filter only lets its own colour through and absorbs the rest. A red filter in white light transmits red, absorbs green and blue.

A red object in blue light appears black (no red light to reflect).

You must be able to recognise and draw these circuit symbols:

Component	Function
Cell / Battery	Provides potential difference (voltage)
Switch (open/closed)	Breaks or completes the circuit
Lamp	Converts electrical energy to light
Resistor (fixed)	Opposes current flow
Variable resistor	Allows resistance to be changed
Ammeter	Measures current (connected in series)
Voltmeter	Measures voltage (connected in parallel)
Thermistor	Resistance decreases as temperature increases
LDR	Resistance decreases as light intensity increases
Diode / LED	Allows current in one direction only
Fuse	Melts if current is too high, breaking circuit

• Current (I) -- flow of charge, measured in amps (A)
• Voltage (V) -- energy per unit charge (potential difference), measured in volts (V)
• Resistance (R) -- opposition to current flow, measured in ohms (Ω)

Rearranged: I = V / R and R = V / I

Ohm's Law: For a conductor at constant temperature, current is directly proportional to voltage (linear I-V graph through the origin).

Series Circuits

• Current: same everywhere (I&sub1; = I&sub2; = I&sub3;)
• Voltage: shared between components (V = V&sub1; + V&sub2; + V&sub3;)
• Resistance: total = sum of all (R = R&sub1; + R&sub2; + R&sub3;)

Parallel Circuits

• Voltage: same across each branch (V&sub1; = V&sub2; = V&sub3;)
• Current: splits at junctions (I = I&sub1; + I&sub2; + I&sub3;)
• Resistance: total is less than the smallest individual resistor (1/R = 1/R&sub1; + 1/R&sub2;)

Power (P) in watts (W). Energy (E) in joules (J). Time (t) in seconds (s).

UK mains supply: 230 V AC, 50 Hz.

Wiring a Plug

• Live (brown) -- carries the voltage, alternates between +325V and -325V
• Neutral (blue) -- completes the circuit, approximately 0 V
• Earth (green/yellow) -- safety wire, connected to the metal case, carries current to ground if a fault occurs

Safety Devices

• Fuse: thin wire that melts if current is too high, breaking the circuit. Always in the live wire.
• Circuit breaker: electromagnetic switch that trips if current is too high. Can be reset (unlike a fuse).
• Earth wire + fuse: if a live wire touches the metal case, large current flows through earth wire, blowing the fuse.

Static charge builds up when electrons are transferred by friction between insulating materials.

• Object gaining electrons becomes negatively charged
• Object losing electrons becomes positively charged
• Like charges repel, unlike charges attract

Uses

• Spray painting (even coating)
• Photocopiers and laser printers
• Electrostatic precipitators (removing pollution from chimneys)

Dangers

• Sparks near flammable gases (fuel tankers -- earthing strap used)
• Lightning

• Permanent magnets produce their own magnetic field (e.g., bar magnets)
• Induced (temporary) magnets only become magnets when placed in a magnetic field
• Like poles repel, unlike poles attract

Magnetic Field Lines

• Go from North to South outside the magnet
• Closer together = stronger field
• Can be plotted using a plotting compass or iron filings

The Earth has a magnetic field. A compass needle points to magnetic north.

A solenoid is a coil of wire that produces a magnetic field when current flows through it. Adding an iron core makes it an electromagnet.

Factors Affecting Strength

• Increase the current
• Increase the number of turns/coils
• Add a soft iron core

Uses of Electromagnets

• Relay: small current in one circuit switches on a larger current in another circuit
• Circuit breaker: electromagnet pulls switch open when current is too high
• Electric bell: electromagnet attracts hammer, breaks circuit, spring pulls back, cycle repeats
• Scrapyard cranes, MRI scanners

A current-carrying wire in a magnetic field experiences a force. This is the motor effect.

Fleming's Left-Hand Rule

• Thumb = Force (motion)
• First finger = Field (N to S)
• Second finger = Current (conventional, + to -)

DC Motor

A coil of wire in a magnetic field. Current flows through the coil, creating a force on each side (one up, one down), causing rotation. A split-ring commutator reverses the current every half turn to keep the motor spinning in the same direction.

To increase speed: increase current, increase number of turns, use stronger magnets.

Faraday's Law

A voltage (EMF) is induced when a conductor moves through a magnetic field, or when a magnetic field changes around a conductor. The induced voltage can be increased by:

• Moving faster
• Using a stronger magnet
• Using more turns of wire

Generators

A coil rotating in a magnetic field produces an alternating voltage (AC). Uses slip rings (for AC output) instead of a commutator.

Transformers

Change the voltage of an AC supply. Two coils wound on an iron core.

• Step-up transformer: more turns on secondary, increases voltage
• Step-down transformer: fewer turns on secondary, decreases voltage

Magnetic Field Around a Bar Magnet

• Field lines go from North to South outside the magnet
• Lines are closest together at the poles (strongest field)
• Field lines never cross

Magnetic Field Around a Straight Wire

• A current-carrying wire produces a magnetic field in concentric circles around the wire
• Use the right-hand grip rule: thumb points in direction of current, fingers curl in direction of field lines
• Field is stronger closer to the wire and with a larger current

Magnetic Field of a Solenoid

• The field inside a solenoid is strong and uniform (parallel lines)
• The field pattern outside is identical to a bar magnet
• Use the right-hand grip rule: fingers curl in direction of current, thumb points to the North pole

The National Grid is a system of cables and transformers that distributes electricity from power stations to homes and businesses across the country.

How It Works

• Power station generates electricity at ~25,000 V
• Step-up transformer increases voltage to 275,000 V or 400,000 V for transmission
• High voltage electricity is transmitted through overhead cables (pylons)
• Step-down transformer reduces voltage to 230 V for domestic use

Why Use High Voltage?

For a given power, increasing the voltage decreases the current (since P = IV).

Lower current means less energy wasted as heat in the cables (since P_waste = I²R).

This makes transmission much more efficient.

An atom consists of a small, dense nucleus containing protons and neutrons, surrounded by electrons orbiting in shells.

Particle	Relative Mass	Relative Charge	Location
Proton	1	+1	Nucleus
Neutron	1	0	Nucleus
Electron	~1/1836 (negligible)	-1	Shells around nucleus

Atomic Number and Mass Number

• Atomic number (Z) = number of protons (defines the element)
• Mass number (A) = number of protons + neutrons
• Number of neutrons = A - Z
• In a neutral atom, number of electrons = number of protons

Isotopes

Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.

Example: Carbon-12 (6 protons, 6 neutrons) and Carbon-14 (6 protons, 8 neutrons) are isotopes of carbon.

Unstable nuclei emit radiation to become more stable. This process is random and spontaneous (cannot be predicted or controlled by external conditions like temperature or pressure).

Types of Radiation

Property	Alpha (α)	Beta (β)	Gamma (γ)
What is it?	2 protons + 2 neutrons (helium nucleus)	High-speed electron from the nucleus	Electromagnetic wave (high frequency)
Charge	+2	-1	0
Mass	4 (heavy)	~0 (very light)	0
Penetration	Stopped by paper / few cm of air	Stopped by thin aluminium (~5 mm)	Reduced by thick lead / concrete
Ionising ability	Strongly ionising	Moderately ionising	Weakly ionising
Deflected by fields?	Yes (deflected slightly by electric/magnetic fields)	Yes (deflected more, opposite direction to alpha)	No

Nuclear Equations

Alpha decay: The nucleus loses 2 protons and 2 neutrons.

Example: Uranium-238 → Thorium-234 + alpha particle

Beta decay: A neutron turns into a proton and emits an electron.

Example: Carbon-14 → Nitrogen-14 + beta particle

Gamma emission: The nucleus releases excess energy as a gamma ray. No change to mass number or atomic number.

The half-life of a radioactive isotope is the time taken for:

• The number of unstable nuclei to halve, OR
• The activity (count rate) to halve

Half-life is constant for a given isotope and is not affected by temperature, pressure, or chemical state.

Half-Life Calculations

After n half-lives, the fraction remaining = (1/2)ⁿ

Uses of Radioactivity

Use	Type of Radiation	Why This Type?
Medical tracers (e.g., thyroid scans)	Gamma	Penetrates the body, detected outside; short half-life reduces exposure
Smoke detectors	Alpha	Ionises air to create a current; smoke absorbs alpha, breaks current, triggers alarm
Carbon dating	Beta (from Carbon-14)	Long half-life (5730 years) allows dating of ancient organic material
Sterilisation of equipment	Gamma	Penetrates packaging to kill bacteria without opening
Cancer treatment (radiotherapy)	Gamma	Focused beams destroy cancer cells
Thickness monitoring (paper/metal)	Beta (paper) / Gamma (metal)	Changes in absorption indicate thickness variation

Dangers of Radiation

• Radiation can ionise atoms in living cells, damaging DNA
• This can cause mutations, leading to cancer
• High doses can cause radiation sickness or cell death
• Alpha is most dangerous if inside the body (inhaled/ingested) -- strongly ionising
• Gamma is most dangerous outside the body -- penetrates through to organs

Safety Precautions

• Keep sources in lead-lined containers when not in use
• Use tongs (never handle with bare hands)
• Minimise exposure time
• Maximise distance from the source
• Use appropriate shielding (lead aprons, concrete walls)

Nuclear Fission

Fission is the splitting of a large, unstable nucleus into two smaller nuclei, releasing energy and neutrons.

• A neutron is absorbed by a heavy nucleus (e.g., uranium-235 or plutonium-239)
• The nucleus becomes unstable and splits into two daughter nuclei + 2 or 3 neutrons + energy
• The released neutrons can cause further fission reactions -- this is a chain reaction
• In a nuclear reactor, control rods (boron) absorb excess neutrons to control the rate of reaction

Nuclear Fusion

Fusion is the joining of two small, light nuclei to form a larger nucleus, releasing huge amounts of energy.

• Example: hydrogen nuclei fuse to form helium -- this is what powers the Sun and other stars
• Requires extremely high temperatures and pressures to overcome the electrostatic repulsion between positive nuclei
• Currently very difficult to achieve and sustain on Earth for power generation

Feature	Fission	Fusion
Process	Splitting a large nucleus	Joining small nuclei
Fuels	Uranium-235, Plutonium-239	Hydrogen isotopes (deuterium, tritium)
Energy released	Large	Even larger (per unit mass)
Conditions	Neutron bombardment	Extremely high temperature and pressure
Waste	Radioactive waste products	Helium (non-radioactive)
Used in	Nuclear power stations, nuclear bombs	Stars, hydrogen bombs, future reactors

Where: Q = energy transferred (J), m = mass (kg), c = specific heat capacity (J/kg°C), ΔT = change in temperature (°C)

The specific heat capacity of a substance is the energy needed to raise the temperature of 1 kg of that substance by 1°C.

Substance	c (J/kg°C)	Note
Water	4200	Very high -- excellent coolant / heat store
Aluminium	900	Heats up faster than water
Copper	390	Low SHC -- heats and cools quickly
Iron	450	Used in cooking pans
Oil	2000	Used in some heaters

Where: Q = energy transferred (J), m = mass (kg), L = specific latent heat (J/kg)

The specific latent heat is the energy needed to change the state of 1 kg of a substance without changing its temperature.

Two Types

• Specific latent heat of fusion (L_f) -- energy to change between solid and liquid (melting/freezing). For water: L_f = 334,000 J/kg
• Specific latent heat of vaporisation (L_v) -- energy to change between liquid and gas (boiling/condensing). For water: L_v = 2,260,000 J/kg

Internal Energy

Internal energy is the total energy stored inside a system. It is the sum of:

• Kinetic energy of all the particles (related to temperature)
• Potential energy of all the particles (related to their positions/bonds)

When you heat a substance, you increase its internal energy. This either raises the temperature (increases kinetic energy) or causes a change of state (increases potential energy).

States of Matter

Property	Solid	Liquid	Gas
Particle arrangement	Fixed, regular pattern	Close but random	Far apart, random
Particle movement	Vibrate in fixed positions	Move around each other	Move quickly in all directions
Forces between particles	Strong	Weaker	Very weak / negligible
Density	High	Medium	Low

State Changes

• Melting: solid → liquid (energy absorbed)
• Boiling / Evaporation: liquid → gas (energy absorbed)
• Freezing: liquid → solid (energy released)
• Condensation: gas → liquid (energy released)
• Sublimation: solid → gas directly (energy absorbed)

Heating Curve

A graph of temperature against time when a substance is heated at a constant rate:

• Rising sections: temperature increases -- energy is increasing the kinetic energy of particles (use Q = mcΔT)
• Flat sections: temperature stays constant -- a state change is occurring. Energy is being used to break bonds between particles (use Q = mL)
• First flat section = melting (solid → liquid)
• Second flat section = boiling (liquid → gas)

Cooling Curve

The reverse process: flat sections show condensation and freezing, where energy is released as bonds form.

Conservation of Energy in Thermal Processes

Energy is always conserved. When an object cools, the thermal energy transferred to the surroundings equals the energy lost by the object. In a closed system, the total internal energy remains constant.

Our solar system contains the Sun, 8 planets, dwarf planets, moons, asteroids, and comets.

Order of Planets (from the Sun)

Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune

Memory aid: My Very Easy Method Just Speeds Up Naming

Feature	Rocky Planets (inner)	Gas Giants (outer)
Examples	Mercury, Venus, Earth, Mars	Jupiter, Saturn, Uranus, Neptune
Size	Smaller	Much larger
Density	Higher	Lower
Surface	Solid, rocky	No solid surface (gas/liquid)

Other Objects

• Moons: natural satellites orbiting planets (e.g., Earth's Moon)
• Asteroids: rocky bodies mostly found in the asteroid belt (between Mars and Jupiter)
• Comets: icy bodies with highly elliptical orbits; develop tails when near the Sun
• Dwarf planets: e.g., Pluto -- orbits the Sun but has not cleared its orbital neighbourhood

Stars About the Same Size as Our Sun

• Nebula -- a cloud of dust and gas (mostly hydrogen)
• Protostar -- gravity pulls the nebula together; it heats up
• Main sequence star -- hydrogen fuses into helium; the outward pressure from fusion balances the inward pull of gravity (equilibrium). Our Sun is here now.
• Red giant -- hydrogen fuel runs low, outer layers expand and cool (turning red)
• Planetary nebula -- outer layers are ejected
• White dwarf -- hot, dense core remains; gradually cools over billions of years

Stars Much Larger than Our Sun

• Nebula → Protostar → Main sequence star
• Red supergiant -- expands even more than a red giant
• Supernova -- catastrophic explosion; elements heavier than iron are formed here
• Neutron star -- extremely dense remnant core, OR
• Black hole -- if the remaining core is massive enough, gravity is so strong that nothing (not even light) can escape

The Hertzsprung-Russell (H-R) diagram is a graph that plots stars by their luminosity (brightness) against their surface temperature.

• Temperature axis goes from hot (left) to cool (right) -- note this is reversed!
• Luminosity axis goes from dim (bottom) to bright (top)

Key Regions

Region	Location on Diagram	Properties
Main sequence	Diagonal band from top-left to bottom-right	Most stars; fusing hydrogen into helium
Red giants / supergiants	Top-right	Cool but very luminous; large size
White dwarfs	Bottom-left	Hot but very dim; small size

As a star evolves, it moves around the H-R diagram. A Sun-like star moves from the main sequence to red giant (top-right), then to white dwarf (bottom-left).

Red Shift

When we observe light from distant galaxies, the wavelengths are longer than expected -- shifted toward the red end of the spectrum. This is called red shift.

• Red shift shows that galaxies are moving away from us
• The further away a galaxy is, the greater the red shift (it is moving away faster)
• This is similar to the Doppler effect for sound (an ambulance siren changes pitch as it moves away)

Evidence for an Expanding Universe

• Red shift of galaxies: nearly all galaxies show red shift, meaning the universe is expanding in all directions
• Hubble's observation: more distant galaxies have greater red shift (moving away faster)
• This does NOT mean we are at the centre -- every point in the universe sees other galaxies moving away (like dots on an inflating balloon)

The Big Bang Theory

The Big Bang theory states that the universe began from a single, extremely hot and dense point approximately 13.8 billion years ago, and has been expanding ever since.

Evidence for the Big Bang

• Red shift -- the universe is expanding, so it must have been smaller in the past
• Cosmic Microwave Background Radiation (CMBR) -- faint microwave radiation detected from all directions in space; this is the remnant heat from the Big Bang, now cooled to about -270°C

Light can be described as a stream of tiny packets of energy called photons.

The energy of a single photon depends on its frequency:

Where: E = energy of the photon (J), h = Planck's constant (6.63 x 10^-34 J s), f = frequency (Hz)

• Higher frequency light (e.g., UV, X-rays, gamma) = higher energy photons
• Lower frequency light (e.g., radio, microwave) = lower energy photons
• Since c = fλ, the equation can also be written as E = hc/λ

The photoelectric effect is the emission of electrons from a metal surface when light of a sufficiently high frequency shines on it.

Key Observations

• Electrons are only emitted if the light frequency is above a certain threshold frequency
• Below the threshold frequency, no electrons are emitted -- no matter how bright the light
• Increasing the brightness (intensity) increases the number of electrons emitted, but NOT their energy
• Increasing the frequency increases the energy of the emitted electrons

Why This Matters

The photoelectric effect cannot be explained by the wave model of light. It provides evidence that light behaves as particles (photons). Each photon transfers its energy to a single electron. If the photon energy (E = hf) is not enough to free the electron, no emission occurs -- regardless of how many photons arrive.

One of the most remarkable discoveries in physics is that light behaves as both a wave and a particle.

Evidence for Wave Behaviour

• Diffraction: light spreads out when passing through a narrow slit
• Interference: light produces bright and dark fringes when two waves overlap (Young's double slit experiment)
• Refraction: light changes direction at a boundary between materials

Evidence for Particle Behaviour

• Photoelectric effect: light ejects electrons from metals -- only explained by photons
• Energy is transferred in discrete packets (quanta), not continuously

Summary

Light is neither purely a wave nor purely a particle. It exhibits wave-particle duality -- it shows wave properties in some experiments (diffraction, interference) and particle properties in others (photoelectric effect). This is a fundamental concept in modern physics.

Practical	Key Points
Hooke's Law	Measure extension of spring with increasing force. Plot F vs e graph. Gradient = k.
Specific Heat Capacity	Heat metal block, measure energy input and temperature change. c = E/(mΔT). Insulate to reduce error.
Resistance (I-V characteristics)	Vary voltage across resistor/lamp/diode. Record I and V. Plot I-V graphs.
Speed of Sound	Measure time for echo over known distance. v = 2d/t. Or use two microphones and a data logger.
Density	Regular solid: measure dimensions and mass, ρ = m/V. Irregular: displacement method.
Refraction	Trace light rays through a glass block. Measure angles of incidence and refraction.

Equations You MUST LEARN

Equation	Quantity
v = d / t	Speed
a = (v - u) / t	Acceleration
F = m x a	Newton's 2nd Law
W = m x g	Weight
M = F x d	Moment
P = F / A	Pressure (solids)
F = k x e	Hooke's Law
V = I x R	Ohm's Law
P = I x V	Electrical Power
E = P x t	Energy transferred
v = f x λ	Wave speed
Efficiency = useful out / total in x 100%	Efficiency
F = B x I x l	Motor effect force

Equations GIVEN on the Formula Sheet

Equation	Quantity
KE = ½mv²	Kinetic energy
GPE = mgh	Gravitational PE
E = mcΔT	Specific heat capacity
P = ρgh	Pressure in liquids
P = I²R	Power (alternative)
Vs/Vp = Ns/Np	Transformer equation
Q = mL	Specific latent heat
E = hf	Photon energy

For any equation in the form A = B x C, draw a triangle:

• Cover what you want to find.
• If two values are side by side: multiply them.
• If one is above the other: divide (top / bottom).

Example with V = I x R

• Find V: cover V, see I x R, so V = I x R
• Find I: cover I, see V over R, so I = V / R
• Find R: cover R, see V over I, so R = V / I

Conversion	Method
km to m	x 1000
m to km	/ 1000
cm to m	/ 100
mm to m	/ 1000
g to kg	/ 1000
kg to g	x 1000
kW to W	x 1000
W to kW	/ 1000
minutes to seconds	x 60
hours to seconds	x 3600
kWh	kWh = power (kW) x time (hours)

Kilowatt-hours (kWh)

1. Forgetting to convert units -- always convert km to m, g to kg, kW to W, minutes to seconds BEFORE calculating.
2. Writing weight in kg -- weight is a force, measured in newtons (N), not kilograms.
3. Saying energy is "used up" -- energy is transferred, not created or destroyed.
4. Confusing mass and weight -- mass is in kg and does not change; weight is in N and depends on gravity.
5. Squaring the wrong term in KE -- only velocity is squared: KE = ½mv², NOT ½(mv)².
6. Getting efficiency above 100% -- you have swapped useful output and total input.
7. Measuring angles from the surface -- always measure from the NORMAL.
8. Saying "heat rises" -- hot AIR rises; heat is transferred by convection in fluids.
9. Forgetting to halve the echo distance -- sound travels there AND back, so divide total distance by 2.
10. Confusing series and parallel rules -- in series: current same, voltage splits. In parallel: voltage same, current splits.
11. Thinking transformers work with DC -- they only work with AC (changing magnetic field needed).
12. Not stating direction for vectors -- velocity, force, and acceleration need a direction.

Command Words

Word	What to do
State	Give a brief, factual answer -- no explanation needed
Describe	Say what happens -- give details of the process or feature
Explain	Say what happens AND why -- link cause and effect
Calculate	Use numbers and an equation -- show your working
Compare	Give similarities AND differences
Suggest	Apply your knowledge to an unfamiliar context
Evaluate	Weigh up both sides and give a conclusion
Justify	Give reasons for your answer using evidence

General Exam Tips

• Show all working -- even if your final answer is wrong, you can get method marks.
• Include units in every answer (m/s, N, J, W, Pa, Ω, etc.).
• Read the question twice -- underline key words.
• Check your answer -- does it make sense? A car is not going 500,000 m/s.
• Use the marks as a guide -- 3 marks = 3 distinct points.
• Draw diagrams clearly with a ruler and label them.
• Circle your final answer to make it clear.

Standard Form

A way of writing very large or very small numbers: A x 10ⁿ where 1 ≤ A < 10.

• Speed of light: 300,000,000 m/s = 3 x 10⁸ m/s
• Charge of electron: 0.00000000000000000016 C = 1.6 x 10^-19 C

Significant Figures

Give your answer to the same number of significant figures as the data in the question (usually 2 or 3 s.f.).

• 4567 to 3 s.f. = 4570
• 0.003456 to 2 s.f. = 0.0035
• Leading zeros are NOT significant