Cambridge IGCSE Physics 0625 — Complete Study Guide

Motion, Forces & Energy

Mechanics · Kinematics · Momentum · Work · Power · Pressure

1.1 Physical Quantities & Measurement

Length is measured with a ruler (mm precision). Volume of irregular solids is found by displacement in a measuring cylinder.

Time is measured with clocks or digital timers. For short intervals, measure multiple periods then divide.

To find the period of a pendulum accurately: time 20 complete oscillations and divide by 20. This reduces the effect of reaction-time error.

Period T = total time / number of oscillations

Average period calculation

EXTENDED Scalar quantities have magnitude only. Vector quantities have both magnitude and direction.

Scalars

Distance · Speed · Time · Mass · Energy · Temperature

Vectors

Force · Weight · Velocity · Acceleration · Momentum · Electric & Gravitational field strength

Resultant = √(A² + B²) θ = tan⁻¹(B/A)

Two vectors at right angles (Pythagoras)

Adding two vectors at right angles using Pythagoras' theorem

1.2 Motion

Speed = distance / time. Velocity = speed in a given direction (vector).

v = s / t average speed = total distance / total time

Speed equations

EXT a = Δv / Δt

Acceleration (Extended)

Free-fall acceleration near Earth's surface: g ≈ 9.8 m/s² (constant, approximately)

Distance–time graph showing different types of motion

Speed–time graph: gradient = acceleration; area under graph = distance

EXT Terminal velocity: When an object falls, air resistance increases until it equals gravity. Net force = 0 → constant velocity.

Forces on a falling object

1.3 Mass & Weight

g = W / m W = mg

Gravitational field strength (g = 9.8 N/kg on Earth)

Mass is constant everywhere. Weight changes with gravitational field strength.

Location	g (N/kg)	Weight of 70 kg person
Earth (surface)	9.8	686 N
Moon	1.6	112 N
Jupiter	24.8	1736 N
Deep space	≈ 0	≈ 0 N

1.4 Density

ρ = m / V

Density (kg/m³ or g/cm³)

Measuring regular solid

Measure dimensions with a ruler → calculate volume geometrically → use ρ = m/V.

Measuring irregular solid

Submerge in water in measuring cylinder. Volume = change in water level reading (displacement method).

Object floats if its density is less than the liquid it's placed in.

Measuring volume by water displacement

1.5 Forces

Hooke's Law: Extension is proportional to force, up to the limit of proportionality.

EXT k = F / x

Spring constant k (N/m or N/cm). F = kx

Load–extension graph showing Hooke's Law and limit of proportionality

1.5.2 Turning Effect of Forces (Moments)

Moment = F × perpendicular distance from pivot

Unit: N m

Principle of Moments: For equilibrium, sum of clockwise moments = sum of anticlockwise moments.

Principle of moments: balanced beam

1.5.3 Centre of Gravity

The centre of gravity is the point through which the entire weight of an object appears to act.

Low centre of gravity → more stable. High centre of gravity → less stable (easier to topple).

1.6 Momentum Extended

p = mv impulse = FΔt = Δ(mv)

Momentum p (kg m/s), Impulse (N s)

F = Δp / Δt

Resultant force as rate of change of momentum

Law of Conservation of Momentum: In a closed system, total momentum before = total momentum after collision.

WORKED EXAMPLE

Cart A (mass 2 kg, velocity 3 m/s) collides with stationary Cart B (mass 3 kg). They stick together. Find final velocity.

Before: p = 2×3 + 3×0 = 6 kg m/s

After: p = (2+3) × v → v = 6/5 = 1.2 m/s

1.7 Energy, Work & Power

Energy stores: kinetic, gravitational potential, chemical, elastic, nuclear, electrostatic, internal (thermal).

W = Fd = ΔE P = W/t = ΔE/t

Work done (J), Power (W)

EXT Eₖ = ½mv² ΔEₚ = mgΔh

Kinetic energy & Change in gravitational PE

EXT efficiency = useful output / total input (× 100%)

Also: efficiency = useful power out / total power in

Sankey diagram: energy input, useful output, and wasted energy

1.7.3 Energy Resources

Source	Renewable?	Reliable?	Environmental Impact
Fossil fuels	No	Yes	CO₂ emissions, air pollution
Nuclear	No	Yes	Radioactive waste
Hydroelectric	Yes	Yes (if rain)	Habitat flooding
Solar (PV)	Yes	No (needs sun)	Low — land use
Wind	Yes	No (needs wind)	Low — noise, visual
Geothermal	Yes	Yes	Very low
Tidal	Yes	Yes	Coastal habitat impact

1.8 Pressure

p = F / A

Pressure (Pa or N/m²)

EXT Δp = ρgΔh

Pressure at depth in a liquid

Pressure in a liquid increases with depth and with liquid density. It acts in all directions.

Thermal Physics

Kinetic Model · States of Matter · Heat Transfer · Thermometry

2.1 Kinetic Particle Model of Matter

Particle arrangements in solids, liquids and gases

T (in K) = θ (in °C) + 273

Converting Celsius to Kelvin

Absolute zero = −273°C = 0 K. At absolute zero, particles have minimum kinetic energy.

EXT pV = constant (at constant temperature)

Boyle's Law — fixed mass of gas

2.1.3 Pressure of a Gas

Increasing temperature → particles move faster → more frequent, harder collisions → higher pressure (constant volume).

Decreasing volume → particles collide more often with walls → higher pressure (constant temperature).

Brownian motion (random zigzag of microscopic particles) is evidence for the kinetic particle model.

2.2 Thermal Properties & Temperature

Solids, liquids, and gases all expand when heated. Gases expand most, solids least.

EXT c = ΔE / (mΔθ)

Specific heat capacity c [J/(kg°C)] — energy to raise 1 kg by 1°C

WORKED EXAMPLE

How much energy to heat 2 kg of water (c = 4200 J/kg°C) from 20°C to 100°C?

ΔE = mcΔθ = 2 × 4200 × (100−20) = 2 × 4200 × 80 = 672 000 J = 672 kJ

2.2.3 Changes of State

Changes of state and energy transfers

During melting and boiling, temperature stays constant even though energy is being supplied (latent heat — breaking bonds).

Evaporation causes cooling: the most energetic molecules escape, leaving the liquid cooler.

2.3 Transfer of Thermal Energy

Conduction

Transfer through solids (and poor liquids/gases) via vibrating particles & free electrons in metals.

Best conductors: metals. Best insulators: wood, rubber, air.

Convection

Transfer in fluids (liquids & gases) via density differences creating convection currents.

Hot fluid rises (less dense); cool fluid sinks (more dense).

Radiation

Infrared radiation — does NOT need a medium. Can travel through vacuum.

Dull black surfaces: best emitters & absorbers. Shiny white: best reflectors.

Convection current created by a heat source

EXT Earth's temperature is maintained by a balance between incoming solar radiation and outgoing radiation. Greenhouse gases affect this balance.

Waves

Wave Properties · Light · EM Spectrum · Sound

3.1 General Properties of Waves

v = fλ

Wave speed (m/s) = frequency (Hz) × wavelength (m)

Transverse Waves

Vibration perpendicular to direction of travel. Examples: EM waves, water waves, seismic S-waves.

Longitudinal Waves

Vibration parallel to direction of travel. Examples: sound waves, seismic P-waves.

Anatomy of a transverse wave

Waves can undergo reflection (bounce off surface), refraction (change speed → change direction), and diffraction (spread through gaps/edges).

EXT Diffraction is greatest when wavelength ≈ gap size.

3.2 Light

Reflection

angle of incidence (i) = angle of reflection (r)

Law of Reflection

Refraction & Snell's Law

EXT n = sin i / sin r n = 1 / sin c

Refractive index n; c = critical angle

Refraction of light at an air–glass boundary

Total Internal Reflection

When light travels from a denser medium and the angle of incidence exceeds the critical angle, all light is reflected back — no refraction.

Optical fibres use total internal reflection to transmit light signals over long distances in telecommunications.

3.2.3 Thin Lenses

Ray diagram: real image formed by a converging lens (object beyond 2F)

3.3 Electromagnetic Spectrum

All EM waves travel at c = 3.0 × 10⁸ m/s in a vacuum. They are transverse waves requiring no medium.

The electromagnetic spectrum ordered by increasing frequency

Region	Uses	Harmful Effects
Radio waves	TV/radio, astronomy, RFID	Minimal
Microwaves	Satellite TV, mobile phones, ovens	Internal heating of cells
Infrared	Grills, remote controls, thermal imaging	Skin burns
Visible light	Vision, photography	None (normal exposure)
Ultraviolet	Security marking, sterilising water	Skin cancer, eye damage
X-rays	Medical scanning, security	Cell mutation/damage
Gamma rays	Sterilisation, cancer treatment	Cell mutation, cancer

3.4 Sound

Sound is a longitudinal wave requiring a medium. It cannot travel through a vacuum.

Speed of sound in air ≈ 330–350 m/s

Compare: light ≈ 3 × 10⁸ m/s

Human hearing range: 20 Hz to 20 000 Hz. Ultrasound: f > 20 kHz.

Loudness & Pitch

Amplitude ↑ → louder sound.
Frequency ↑ → higher pitch.

Ultrasound Uses

Medical imaging (soft tissue), non-destructive testing of materials, sonar (depth finding).

Electricity & Magnetism

Electric Circuits · Electromagnetic Effects · Magnetism

4.1 Magnetism

Like poles repel; unlike poles attract. Magnetic materials: iron, steel, nickel, cobalt.

Temporary magnets (soft iron): easily magnetised/demagnetised — used in electromagnets.

Permanent magnets (steel): hard to demagnetise — used in compasses.

Magnetic field lines run from N to S outside the magnet, and from S to N inside.

4.2 Electrical Quantities

R = V/I P = IV E = IVt

Resistance (Ω), Power (W), Energy (J)

EXT I = Q/t V = W/Q E_emf = W/Q

Current, Potential Difference, EMF

For a metallic conductor: Resistance ∝ length; Resistance ∝ 1/cross-sectional area.

I–V characteristics: ohmic resistor (linear), filament lamp (non-linear), diode (one-way)

4.3 Electric Circuits

Series Circuit

I_total = I₁ = I₂
V_total = V₁ + V₂
R_total = R₁ + R₂

Series rules

Parallel Circuit

V same across all branches
I_total = I₁ + I₂
EXT 1/R = 1/R₁ + 1/R₂

Parallel rules

The switch must always be in the LIVE wire so that when switched off, the appliance is fully de-energised and safe to touch.

4.5 Electromagnetic Effects

A conductor moving through a magnetic field, or a changing magnetic field linking a conductor, induces an EMF.

Induced EMF increases with: faster movement, stronger magnet, more turns of wire.

V_p / V_s = N_p / N_s EXT I_p V_p = I_s V_s

Transformer equations

EXT P = I²R

Power loss in cables — minimised by using high voltage

Step-up transformer: more secondary turns → higher voltage

Nuclear Physics

Atomic Model · Radioactivity · Half-life · Safety

5.1 Nuclear Model of the Atom

ᴬ_Z X : A = mass number, Z = proton number
Neutrons = A − Z

Nuclide notation

Particle	Charge	Mass
Proton	+1	1
Neutron	0	1
Electron	−1	≈0

Isotopes: same proton number Z, different neutron number (different A).

EXT Rutherford α-scattering: most α-particles pass through (mostly empty space); very few bounce back → small, dense, positive nucleus.

EXT Fission: heavy nucleus splits → energy. Fusion: light nuclei join → heavier nucleus + energy (powers the Sun).

5.2 Radioactivity

Type	Nature	Charge	Range in air	Blocked by	Ionising
Alpha (α)	2p + 2n (He nucleus)	+2	A few cm	Paper/skin	Highest
Beta (β⁻)	Fast electron	−1	~1 m	Few mm Al	Medium
Gamma (γ)	EM wave (photon)	0	Unlimited	Several cm Pb	Lowest

Half-life: time for activity (or number of nuclei) to halve
After n half-lives: N = N₀ × (½)ⁿ

Radioactive decay

Decay curve — each half-life halves the remaining activity

Safety

• Use tongs — never handle with bare hands. • Minimise exposure time. • Keep distance from source. • Use lead or concrete shielding. • Store in lead-lined containers.

Effects on living tissue: cell death, gene mutation, cancer.

EXAMINATION CENTRE

Practice Exam

MCQ · True/False · Calculations · Short Answer across all 6 topics

Section A — Multiple Choice

MCQ[1 mark] Topic 1 — Motion

A car travels 120 m in 8 s. What is its average speed?

A10 m/s
B12 m/s
C15 m/s
D960 m/s

MCQ[1 mark] Topic 1 — Vectors

Which of the following is a vector quantity?

ATemperature
BVelocity
CMass
DSpeed

MCQ[1 mark] Topic 1 — Hooke's Law

A spring has constant k = 50 N/m. What force produces an extension of 4 cm?

A2 N
B12.5 N
C200 N
D0.08 N

MCQ[1 mark] Topic 2 — States

Which process occurs at constant temperature?

AHeating water from 20°C to 80°C
BCooling a gas at constant volume
CMelting of ice at 0°C
DHeating a solid above its melting point

MCQ[1 mark] Topic 2 — Temperature

What is −40°C in Kelvin?

A313 K
B233 K
C40 K
D−233 K

MCQ[1 mark] Topic 3 — Waves

A wave has frequency 500 Hz and wavelength 0.68 m. What is its speed?

A735 m/s
B0.00136 m/s
C340 m/s
D1.36 m/s

MCQ[1 mark] Topic 3 — EM Spectrum

Which EM wave has the longest wavelength?

AGamma rays
BX-rays
CUltraviolet
DRadio waves

MCQ[1 mark] Topic 4 — Circuits

A resistor has 12 V across it and 3 A through it. What is its resistance?

A36 Ω
B4 Ω
C0.25 Ω
D9 Ω

MCQ[1 mark] Topic 5 — Nuclear

An alpha particle consists of:

A2 protons and 2 electrons
B1 proton and 1 neutron
C2 protons and 2 neutrons
D4 protons only

MCQ[1 mark] Topic 6 — Universe

What evidence shows the Universe is expanding?

ABlueshift of distant galaxies
BRedshift of distant galaxies
CThe Sun producing nuclear fusion
DThe Moon orbiting Earth

Section B — True / False

T/F[1 mark]

Weight is a scalar quantity.

T/F[1 mark]

Convection can occur in a vacuum.

T/F[1 mark]

Sound waves are transverse waves.

T/F[1 mark]

In a parallel circuit, the current through each branch is the same.

T/F[1 mark]

Gamma radiation has the highest penetrating power of all three types of nuclear emission.

Section C — Calculation Problems

CALC[3 marks] Topic 1 — Energy

A ball (mass 0.5 kg) is thrown upward at 10 m/s. Calculate: (a) its kinetic energy at release, (b) its maximum height. (g = 9.8 m/s², ignore air resistance.)

CALC[2 marks] Topic 1 — Moments

A 4 N force produces a moment of 0.8 N m about a pivot. Find the perpendicular distance from the force to the pivot.

CALC[3 marks] Topic 2 — SHC

How much energy is needed to heat 3 kg of aluminium (c = 900 J/kg°C) from 20°C to 120°C?

CALC[3 marks] Topic 4 — Transformer

A transformer: N_p = 200, N_s = 1000, V_p = 230 V, I_p = 5 A (100% efficient). Find V_s and I_s.

CALC[3 marks] Topic 5 — Half-life

A sample has an initial count rate of 640 counts/min. Half-life = 4 hours. Find count rate after 16 hours.

CALC[2 marks] Topic 4 — Parallel R

Find the combined resistance of 6 Ω and 12 Ω in parallel.

Section D — Short Answer

SHORT[3 marks] Topic 2

Explain why dark, dull clothing makes you warmer in the sun, but light, shiny clothing keeps you cooler.

SHORT[4 marks] Topic 3

Describe how the frequency and amplitude of a sound wave affect what is heard.

SHORT[3 marks] Topic 5

State three safety precautions when handling radioactive sources in a laboratory.

SHORT[4 marks] Topic 1

Describe the motion of an object dropped from rest until it reaches terminal velocity. Refer to the forces at each stage.

SHORT[3 marks] Topic 6

Explain what redshift is and why it supports the Big Bang Theory.

—

Auto-graded score (MCQ + T/F, out of 15)

Section C & D are self-assessed using the model answers shown above.

Complete PhysicsStudy Guid Home

1.1 Physical Quantities & Measurement

Scalars

Vectors

1.2 Motion

1.3 Mass & Weight

1.4 Density

Measuring regular solid

Measuring irregular solid

1.5 Forces

1.5.2 Turning Effect of Forces (Moments)

1.5.3 Centre of Gravity

1.6 Momentum Extended

1.7 Energy, Work & Power

1.7.3 Energy Resources

1.8 Pressure

2.1 Kinetic Particle Model of Matter

2.1.3 Pressure of a Gas

2.2 Thermal Properties & Temperature

2.2.3 Changes of State

2.3 Transfer of Thermal Energy

Conduction

Convection

Radiation

3.1 General Properties of Waves

Transverse Waves

Longitudinal Waves

3.2 Light

Reflection

Refraction & Snell's Law

Total Internal Reflection

3.2.3 Thin Lenses

3.3 Electromagnetic Spectrum

3.4 Sound

Loudness & Pitch

Ultrasound Uses

4.1 Magnetism

4.2 Electrical Quantities

4.3 Electric Circuits

Series Circuit

Parallel Circuit

4.5 Electromagnetic Effects

5.1 Nuclear Model of the Atom

5.2 Radioactivity

Safety

6.1 The Earth & Solar System

6.2 Stars & The Universe

The Universe & Big Bang

Practice Exam

Section A — Multiple Choice

Section B — True / False

Section C — Calculation Problems

Section D — Short Answer

Complete Physics
Study Guid Home