ALL of Edexcel IGCSE Physics 9-1 | PAPER 2 | IGCSE Physics Revision | SCIENCE WITH HAZEL

Main ideas / lessons covered (IGCSE Physics 9–1 Paper 2 revision)

Core: speed / velocity / acceleration from motion graphs

Use formula triangles (and write the full equation)

• Distance (D): ( D = v \times t )
• Speed / velocity (v): ( v = \dfrac{D}{t} )
• Time (t): ( t = \dfrac{D}{v} )

Distance–time graph (y-axis = distance)

• Speed at a point: take the distance/time using values read from the graph.
• Stationary time: look for flat (constant distance) sections of the graph.

Velocity–time graph

• Acceleration is the gradient, found using:
  • ( a = \dfrac{v - u}{t} ) (final speed minus initial speed over time)
• Distance travelled from a velocity–time graph: the area under the graph.
  • Break the area into shapes (triangles/rectangles/trapeziums) and add areas.

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Stopping distance / kinematics with deceleration

• Use equation (shown in example):
  • ( v^2 = u^2 + 2as )
• Key substitutions in stopping problems:
  • Brakes applied → acceleration is negative (deceleration)
  • “Just before brakes” corresponds to initial velocity (u)
  • At complete stop, final velocity (v = 0)
• Final answers requested to specific significant figures (e.g., two s.f.).

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Exam question strategies emphasized

• Don’t just “read options first”—work out the answer from understanding, then match to options.
• When asked for “explain”, include required concept keywords (e.g., “constant means same velocity everywhere”, “stationary means velocity = 0”).
• For reliability in experiments: repeat measurements and use averages.

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Momentum (conservation) and collisions

Momentum equation

• ( p = mv )
• Convert units correctly (e.g., grams → kilograms).

Conservation of momentum

• ( \text{momentum before} = \text{momentum after} )

Recoil / opposite directions

• Use signs implicitly by concluding the direction (often negative velocity).

Inelastic collisions (stick together)

• Treat combined mass as one object:
  • ( v = \dfrac{\text{total initial momentum}}{\text{total final mass}} )

Force from stopping time

• Use change in momentum over time:
  • ( F = \dfrac{\Delta p}{\Delta t} )

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Moments (torque) and turning effects

• Moment equation:
  • ( \text{Moment} = F \times d )
• (d) = perpendicular distance from pivot.
• Balanced forces:
  • Clockwise moment = anticlockwise moment

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Work, energy, power

• Work done / energy transferred:
  • ( W = F \times d )
  • Work and energy measured in joules
• Gravitational potential energy:
  • ( E_{gpe} = mgh )
• Power:
  • ( P = \dfrac{W}{t} )
  • Unit: watts (W = J/s)

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Thermal energy transfer: conduction, convection, radiation

Conduction

• Occurs mainly in solids
• Metals conduct well due to delocalized/free electrons
• Insulators (e.g., wood/plastics/air) conduct poorly

Convection

• Occurs in liquids and gases
• Driven by density changes (warm fluid rises, cool sinks)
• Examples: radiators, convection currents over a cup of coffee
• Lid can reduce convection losses

Radiation

• Travels through solids, liquids, and gases (via electromagnetic waves)
• Colour matters:
  • White/shiny surfaces reflect IR → less absorption
  • Dark/matt surfaces absorb IR → more heating

Thermos flask explanation (conceptual)

• Vacuum: no conduction/convection
• Silvered surfaces: reflect IR radiation
• Lid: reduces convection

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Electrons, static electricity, and electrical safety (high-level)

• Static charging = electron transfer
• Balloons/polythene become charged due to friction
• Earthing wire provides a safe low-resistance path to ground
• Safety devices: fuses vs circuit breakers
  • Circuit breakers reset faster than replacing a melted fuse

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Electricity basics: circuit components and rules

Components & measurement

• Symbol knowledge for: cells/battery, lamp, resistor, variable resistor, thermistor, diode/LED, ammeter, voltmeter, fuse/circuit breaker.

Circuit rules

• Series circuit
  • Current is the same everywhere
  • Voltages add up to total
• Parallel circuit
  • Voltage is the same across components
  • Currents add to total

Resistance and Ohm’s law (qualitative graphs)

• ( V \propto I ) for ohmic conductors (straight line through origin)
• Filament bulb and diode do not obey Ohm’s law (non-linear curves)

Charge and energy calculations

• ( Q = It )
• ( W = VQ ) (work/energy in joules)

Power and current

• ( P = VI )
• Used for finding current and choosing appropriate fuse ratings.

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Waves and optics

Wave types

• Transverse waves: vibration perpendicular to travel direction
• Longitudinal waves: vibration parallel to travel direction
• Key wave equation:
  • ( v = f\lambda )

Period / frequency

• ( f = \dfrac{1}{T} )

Reflection / refraction / critical angle

• Reflection: angle incidence = angle reflection
• Refraction: bending due to speed change between media
• Refractive index:
  • ( n = \dfrac{\sin i}{\sin r} )
• Critical angle:
  • If ( i > c ) → total internal reflection (used in fibre optics)

Echoes and sound properties

• Echo timing involves total travel time; distance is one-way.
• Ultrasound: ( f > 20\,000 ) Hz
• Infrasound: ( f < 20 ) Hz
• Pitch ↔ frequency, loudness ↔ amplitude

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Electromagnetic spectrum (and applications/dangers)

• Order (longest wavelength → shortest): radio, microwaves, infrared, visible, ultraviolet, x-rays, gamma

Example uses

• radio: communications
• microwaves: satellite/cooking
• infrared: remote controls/heat
• UV: tanning/banknote checking
• x-rays: medical imaging
• gamma: sterilisation

Dangers

• IR: burns (heat)
• UV: skin cancer risk; reduce with sunscreen/clothing/sunglasses
• x-rays/gamma: limit exposure; shielding/short handling times

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Energy transfers & efficiency

• Energy is conserved: converted between forms
• Efficiency:
  • ( \text{efficiency} = \dfrac{\text{useful energy out}}{\text{total energy in}} \times 100\% )
• Sankey diagrams: show wasted energy as a larger branch.

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Density, pressure, states of matter

Density

• ( \rho = \dfrac{m}{V} )
• Symmetric objects: measure dimensions
• Irregular objects: displacement method

Pressure

• ( P = \dfrac{F}{A} )
• In liquids:
  • Pressure increases with depth
  • ( \Delta P = \rho g h ) (given as pressure difference = height × density × g)

Pressure with particles and temperature

• Gas pressure arises from particle collisions:
  • pressure = force/area due to collisions
• Increasing temperature → higher particle kinetic energy → more frequent/forceful collisions → higher pressure
• Absolute zero conversion:
  • ( K = ^\circ C + 273 )

State changes

• melting, freezing, evaporation/boiling, condensation (and simultaneous evaporation/condensation in closed containers).

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Magnetism and electromagnetism

• Magnetic metals: iron, steel, cobalt, nickel
• Magnetic field lines drawn using:
  • iron filings or plotting compasses
• Soft vs hard magnetic materials:
  • soft loses magnetism easily, hard retains
• Magnetism and electromagnets:
  • stronger field via higher current, more turns (solenoid), iron core

Motor effect

• Current-carrying wire in magnetic field experiences a force → causes rotation
• Use Fleming’s left-hand rule (direction of force/magnetic field/current)

Generator effect / electromagnetic induction

• Moving a wire in a magnetic field induces voltage/current
• Use Fleming’s right-hand rule for direction

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Transformers

• Purpose: step up/down voltage using AC
• Transformers have:
  • primary and secondary coils
  • soft iron core to strengthen changing magnetic field
• Key equation (turns ratio):
  • ( \dfrac{V_p}{V_s} = \dfrac{N_p}{N_s} )
• Step-down transformer: output voltage lower than input.

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Atomic structure and radiation (radioactivity) + nuclear physics

Atom model basics

• Nucleus contains:
  • protons (positive), neutrons (neutral)
• Electrons orbit nucleus in shells
• Atomic number = protons
• Mass number = protons + neutrons
• Isotopes: same atomic number, different neutron number

Radiation types: alpha, beta, gamma

• Alpha:
  • relatively heavy, highly ionising, short range
  • causes atom to lose 2 protons and 2 neutrons
• Beta:
  • electron emitted; proton number changes by +1; mass number unchanged
• Gamma:
  • electromagnetic radiation; no change to mass or atomic number
• Penetration:
  • alpha stopped by paper/aluminium foil; gamma much more penetrating (lead/concrete)

Half-life

• Definition: time for activity (or number of nuclei) to halve
• Background radiation must be subtracted when measuring
• Graphing activity vs time: decreases in steps/curve based on repeated halving

Uses/dangers of radiation

• Alpha in smoke alarms (ionisation current; stopped by smoke particles)
• Beta used in thickness checking (foil production control)
• Medical tracers (e.g., radioactive iodine; diagnostic use)
• Risks:
  • ionising radiation can cause mutations → cancer
  • protective measures: shielding (lead), distance, tongs, badges/film exposure tracking

Nuclear fission and chain reaction

• Fission: splitting of a heavy nucleus (e.g., U-235) by a neutron
• Releases:
  • energy + extra neutrons (enables chain reaction)
• Control methods:
  • control rods absorb neutrons
  • moderator slows neutrons
  • coolant removes heat; shielding protects workers
• Nuclear fission produces daughter nuclei and additional neutrons (mass/charge balance used in equations).

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Astronomy and cosmology overview

• Solar system order and basic definitions:
  • galaxy = billions of stars
  • universe = billions of galaxies
  • Milky Way is one galaxy
• Orbits:
  • planets/comets in elliptical paths; comets have more elongated orbits

Star life cycle

• nebula → main sequence (hydrogen fusion) → later stages depending on mass → endpoints (white dwarf / neutron star / black hole) via supernova for large stars

Brightness of stars

• apparent brightness vs absolute brightness vs luminosity

Big Bang evidence

• Cosmic Microwave Background Radiation (CMB)
• redshift (Doppler effect for galaxies moving away)

Redshift calculation approach

• compare wavelength change to speed of light using Doppler-effect relation

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Speakers / sources featured

• Speaker: “Science with Hazel” (Hazel)