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Prism Physics

The course

47 chapters and 298 lessons, from measurement and motion to the nucleus and relativity, grouped into 7 topics. Start anywhere; each lesson links back to the ideas it builds on.

Mechanics

Measurement, vectors and calculus, motion, forces, energy, rotation, gravity, oscillations, fluids and elasticity.

Chapter 01

Introduction to Physics

What physics is, and the units, dimensions and rough numbers it runs on.

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  1. 01What Is Physics?Watching nature's chess game and guessing the rules.
  2. 02Units & the SI SystemA measurement is a number times a unit, and the world agrees on seven base units.
  3. 03DimensionsStrip a quantity down to powers of mass, length and time.
  4. 04Using DimensionsA quick test that catches wrong formulas, converts units and even guesses laws.
  5. 05Orders of Magnitude & EstimationFrom protons to quasars, and how to estimate anything to the nearest power of ten.
Chapter 02

The Mathematical Toolkit

Vectors, calculus and honest numbers: the language physics is written in.

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  1. 01Scalars & VectorsWhy 3 + 4 is sometimes 5: quantities that carry a direction.
  2. 02Adding VectorsHead-to-tail, parallelograms, and the law that gives the size of a sum.
  3. 03Scaling & SubtractingStretching, flipping, unit vectors and subtraction as adding the reverse.
  4. 04Components & Unit VectorsBreak any arrow into x, y and z shadows, and adding becomes arithmetic.
  5. 05The Dot ProductMultiply two arrows, get a number: how much one points along the other.
  6. 06The Cross ProductMultiply two arrows, get a third one standing perpendicular to both.
  7. 07Derivatives: Measuring ChangeZoom into a curve until it looks straight. Its slope is the derivative.
  8. 08Peaks & ValleysWhere the slope is zero, something interesting is happening.
  9. 09Integration: Adding Up SliversSlice an area into thin bars, add them all, and let the slices vanish.
  10. 10Significant FiguresEvery digit you write is a promise. Keep only the ones you can keep.
  11. 11Errors & UncertaintyMeasure ten times, and the scatter tells you how much to trust the average.
Chapter 03

Describing Motion

Kinematics: where things are, how fast they go, and who is watching.

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  1. 01Rest, Motion & FramesIs your phone moving right now? It depends entirely on who is asking.
  2. 02Distance vs DisplacementThe length of the journey versus the arrow from start to finish.
  3. 03Speed: Average & InstantaneousA road trip's summary versus what the speedometer says right now.
  4. 04Velocity & Position VectorsSpeed with a direction, built from the arrow that tracks where you are.
  5. 05AccelerationHow quickly velocity changes, in size, in direction, or both.
  6. 06Equations of MotionThree equations that solve every straight-line, constant-acceleration problem.
  7. 07Free FallDrop it, throw it up: gravity runs the same equations every time.
  8. 08Motion in a PlaneTwo straight-line problems wearing a trench coat.
  9. 09Projectile MotionLaunch angles, ranges and heights: explore every arc a ball can trace.
  10. 10Changing FramesRivers, rain and moving trains: velocities as seen by different observers.
Chapter 04

The Forces of Nature

Every push and pull you have ever felt comes from just four fundamental interactions.

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  1. 01What Is a Force?A force is always one object acting on another, and it never comes alone.
  2. 02Gravity: The Universal PullEverything pulls on everything, but you only notice when a planet is involved.
  3. 03Electromagnetic Forces EverywhereEvery touch, tug and bounce is electromagnetism in disguise.
  4. 04Nuclear, Weak & the Limits of Classical PhysicsTwo short-range forces rule the nucleus, and classical physics has a border.
Chapter 05

Newton's Laws of Motion

Three short laws that turn forces into predictions.

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  1. 01The First Law & Inertial FramesZero net force means zero acceleration, but only if you are watching from the right frame.
  2. 02The Second Law: F = maForce sets acceleration, and mass decides how much.
  3. 03Free-Body DiagramsA four-step recipe that makes force problems almost mechanical.
  4. 04The Third Law & TensionEqual and opposite, but never on the same body. Plus what a rope really does.
  5. 05Pseudo ForcesWorking inside an accelerating car or lift? Add one imaginary force and carry on.
  6. 06The Horse-and-Cart Puzzle & InertiaIf the cart pulls back as hard as the horse pulls forward, how does anything move?
Chapter 06

Friction

The force that wears out shoes and also lets you walk in them.

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  1. 01Friction & the Contact ForceOne contact force, two parts: the push straight out and the drag along the surface.
  2. 02Kinetic FrictionWhen surfaces slide, friction opposes the slipping and has a fixed size.
  3. 03Static FrictionA self-adjusting force that holds things together, up to a limit.
  4. 04Laws of Friction & Its OriginFour compact rules, a table of numbers, and a look at surfaces up close.
  5. 05Measuring FrictionA hanging weight or a tilting plank is all you need to measure μ.
Chapter 07

Circular Motion

Moving in a circle means accelerating all the time, even at constant speed.

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  1. 01Angles, Angular Velocity & Angular AccelerationDescribe circling motion with an angle, and everything else follows.
  2. 02Centripetal AccelerationConstant speed, changing direction: the acceleration points at the centre.
  3. 03The Force Behind Circular MotionSomething has to pull inward. Centripetal force is a job, not a new kind of force.
  4. 04Turning Corners & Banked RoadsFriction steers a car round a flat bend; tilting the road lets gravity help.
  5. 05Rotating Frames & Centrifugal ForceOn a spinning platform, you need an outward pseudo force to make Newton's laws work.
Chapter 08

Work & Energy

Energy can move between forms, but the books always balance.

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  1. 01Work & Kinetic EnergyPush something along its path and you change its energy of motion by exactly the work done.
  2. 02Calculating WorkConstant forces, springs and sideways forces: three cases that cover most problems.
  3. 03PowerNot how much work, but how fast.
  4. 04Conservative Forces & Potential EnergySome forces give back every joule they take. Those are the ones that store energy.
  5. 05Conservation of EnergyKinetic plus potential stays constant, until friction takes its cut.
Chapter 09

Centre of Mass, Momentum & Collisions

Find the one point that moves simply, and the quantity that never changes.

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  1. 01The Centre of MassA spinning, tumbling object still has one point that moves like a simple particle.
  2. 02Centre of Mass of Solid BodiesSlice the body into tiny pieces and let integration do the averaging.
  3. 03How the Centre of Mass MovesInternal forces can't move it. Only outside forces can.
  4. 04Linear Momentum & Its ConservationMass times velocity, added up over a system, refuses to change unless pushed from outside.
  5. 05Rocket PropulsionThrow mass backwards fast enough and you go forwards, with nothing to push against.
  6. 06Collisions: Elastic, Inelastic & In BetweenMomentum always survives a collision; kinetic energy only sometimes.
  7. 07Elastic Collisions in 1D & 2DEqual masses swap velocities; a ping-pong ball bounces off a truck.
  8. 08ImpulseA short, hard hit and a long, gentle push can change momentum by the same amount.
Chapter 10

Rotational Mechanics

Everything Newton taught us about pushing, rewritten for turning.

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  1. 01Rotation of a Rigid BodyEvery point goes round in a circle, and all of them share one angle.
  2. 02TorqueTurning effect depends on how hard, where, and in which direction you push.
  3. 03Torque Makes Things Spin Up: τ = IαTorque plays the role of force; moment of inertia plays the role of mass.
  4. 04Bodies in EquilibriumBalance the forces and balance the torques, and nothing moves.
  5. 05Angular Momentum & Its ConservationPull your arms in and you spin faster. Nothing outside had to push.
  6. 06Rotational Kinetic Energy, Work & PowerA spinning wheel stores energy in the motion of all its parts.
  7. 07Calculating Moment of InertiaAdd up mass times distance squared, one slice at a time.
  8. 08Parallel & Perpendicular Axis TheoremsTwo shortcuts that turn one known moment of inertia into many.
  9. 09Rolling: Rotation Plus TranslationThe bottom of a rolling wheel is momentarily at rest; the top moves twice as fast as the centre.
Chapter 11

Gravitation

The same pull that drops an apple keeps the Moon in its orbit.

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  1. 01The Universal Law of GravitationNewton compared an apple with the Moon and found an inverse-square law.
  2. 02Weighing the Earth: Measuring GA twisted fibre, a mirror and a beam of light measure the feeblest force in nature.
  3. 03Gravitational Potential EnergyFar apart counts as zero, so every bound pair has negative energy.
  4. 04Gravitational PotentialPotential energy per kilogram: a map of how deep the gravitational well is.
  5. 05The Gravitational FieldEach mass reshapes the space around it; other masses feel the shape.
  6. 06How g ChangesClimb a mountain or descend a mine and you weigh a little less either way.
  7. 07Satellites, Orbits & Kepler's LawsAn orbit is a fall that keeps missing the ground.
  8. 08Escape Velocity & Black HolesLaunch fast enough and you never come back. Squeeze a star enough and even light can't leave.
Chapter 12

Simple Harmonic Motion

Pull it, let go, and watch nature's favourite rhythm appear.

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  1. 01What Is Simple Harmonic Motion?A force that always points home, growing with distance, makes a perfect rhythm.
  2. 02The Equation of SHMOne sine curve, three knobs: amplitude, angular frequency and phase.
  3. 03SHM as a Shadow of Circular MotionWatch a point go round a circle from the side, and it bobs in SHM.
  4. 04Energy in SHMEnergy sloshes between spring and motion while the total stays fixed.
  5. 05The Simple PendulumFor small swings, a pendulum keeps time regardless of how far it swings.
  6. 06Physical & Torsional PendulumsReal swinging objects and twisting wires follow the same rhythm with I in charge.
  7. 07Combining Two OscillationsAdd two rhythms along a line and you get another; add them at right angles and you draw ellipses.
  8. 08Damped & Forced Oscillations; ResonanceFriction makes swings die away; a well-timed push makes them grow.
Chapter 13

Fluid Mechanics

Push on a liquid and it pushes back everywhere at once.

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  1. 01Pressure in a FluidPressure depends on depth, not on the shape of the container.
  2. 02Pascal's Law & Hydraulic MachinesSqueeze a liquid anywhere and the extra pressure arrives everywhere.
  3. 03Atmospheric Pressure, Barometers & ManometersWe live at the bottom of an ocean of air.
  4. 04Archimedes' Principle & FloatingA fluid pushes up on anything in it with the weight of the fluid it shoves aside.
  5. 05Fluids in Accelerating ContainersIn a lift, gravity seems stronger; in an accelerating truck, the water surface tilts.
  6. 06Fluid Flow & the Equation of ContinuityWhat goes in must come out: narrow pipes make fluids hurry.
  7. 07Bernoulli's EquationWhere a fluid speeds up, its pressure drops.
  8. 08Bernoulli at WorkLeaking tanks, flow meters, perfume sprays and a swinging cricket ball.
Chapter 14

Some Mechanical Properties of Matter

Why solids spring back, liquids bead up and honey pours slowly.

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  1. 01Molecules, Bonds & States of MatterOne potential-energy curve explains solids, liquids and gases.
  2. 02Elasticity, Stress & StrainInternal forces per area, and how much the body gives.
  3. 03Hooke's Law & the Elastic ModuliFor small deformations, stress is proportional to strain.
  4. 04Beyond Hooke: Stress–Strain CurvesStretch too far and the wire never comes back.
  5. 05Elastic Energy & Measuring Young's ModulusStretching a wire stores energy; a careful experiment measures how stiff it is.
  6. 06Surface TensionA liquid surface behaves like a stretched skin.
  7. 07Surface Energy & Pressure in Drops and BubblesMaking new surface costs energy; curved surfaces squeeze what's inside.
  8. 08Contact Angle & Capillary RiseWater climbs a thin glass tube; mercury sinks in it.
  9. 09Viscosity & Flow Through TubesInternal friction: why honey pours slowly and pipes need pressure.
  10. 10Stokes' Law & Terminal VelocityA falling ball speeds up until drag and buoyancy balance its weight.

Waves & Sound

Travelling and standing waves on strings, and the physics of sound.

Chapter 15

Wave Motion & Waves on a String

Energy can travel without anything travelling with it.

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  1. 01Wave Motion & PulsesA disturbance travels; the medium stays where it is.
  2. 02Sine WavesShake the end in SHM and every point copies it, a little later.
  3. 03Wave Speed & Power on a StringTension makes waves fast; heaviness makes them slow. Energy flows with them.
  4. 04Superposition & InterferenceWaves pass through each other untouched, adding as they overlap.
  5. 05Reflection & TransmissionA fixed end flips the pulse; a free end doesn't.
  6. 06Standing WavesTwo opposite waves make a pattern that oscillates in place.
  7. 07Normal Modes of a StringA string can only sing at certain notes: its harmonics.
  8. 08Laws of Vibrating Strings & the SonometerShorter, tighter or lighter strings play higher notes.
  9. 09Transverse, Longitudinal & Polarized WavesWhich way does the medium move compared with the wave?
Chapter 16

Sound Waves

Pressure ripples that we hear, measure, tune and sometimes break the sound barrier with.

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  1. 01What Sound IsA vibrating source sends compressions and rarefactions racing through the air.
  2. 02Displacement & Pressure WavesWhere the air moves most, the pressure changes least.
  3. 03The Speed of SoundStiffness speeds sound up, density slows it; the rest is getting the stiffness of air right.
  4. 04Intensity, Decibels, Pitch & QualityHow loud, how high and what kind of sound: three numbers for what we hear.
  5. 05Interference & Reflection of SoundTwo sounds can add to silence, if they stay in step.
  6. 06Air Columns & Organ PipesA pipe closed at one end plays only odd harmonics; an open pipe plays them all.
  7. 07Measuring the Speed of SoundFind two resonances half a wavelength apart, multiply by the frequency.
  8. 08BeatsTwo almost-equal notes swell and fade together.
  9. 09Diffraction & the Doppler EffectSound bends round corners, and an approaching siren sounds higher.
  10. 10Sonic Booms, Musical Scales & AcousticsFaster than sound, sweeter than noise, and clearer in a well-designed hall.

Light & Optics

Interference and diffraction, mirrors and lenses, instruments, spectra, the speed of light and photometry.

Chapter 17

Light Waves

Fringes, colours, haloes and glare: what light does because it is a wave.

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  1. 01Light: Waves or Particles?A three-hundred-year argument, and what light turned out to be.
  2. 02Huygens' PrincipleEvery point on a wavefront is a new source, and the laws of reflection and refraction follow.
  3. 03Young's Double-Slit ExperimentTwo slits, one light: bright and dark stripes that measure the wavelength.
  4. 04Optical PathA centimetre of glass counts as one and a half centimetres of vacuum.
  5. 05Colours of Thin FilmsWhy a soap bubble shimmers: light reflected from its two faces interferes.
  6. 06Fresnel Biprism & Coherent SourcesWhy two bulbs never make fringes, and how to fake two coherent sources from one.
  7. 07Diffraction by a Single SlitSqueeze light through a slit and it spreads: the narrower the slit, the wider the spread.
  8. 08Round Holes, Sharp Edges & ResolutionNo lens can focus a star to a point, which limits how much detail any instrument can see.
  9. 09Scattering: Blue Skies & Red SunsetsAir molecules scatter blue light far more than red, and that paints the sky.
  10. 10Polarization of LightWhich way the electric field points, and how sunglasses use it to kill glare.
Chapter 18

Geometrical Optics

Mirrors, prisms and lenses: where light goes when we treat it as rays.

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  1. 01Reflection & Plane MirrorsWhy your reflection seems to stand as far behind the mirror as you stand in front.
  2. 02Spherical Mirrors & the Sign ConventionThe vocabulary of curved mirrors, and a sign rule that makes one formula fit every case.
  3. 03The Mirror Formula & MagnificationOne equation finds every mirror image; another tells you its size and whether it's upside down.
  4. 04Refraction at a Flat SurfaceWhy a pool looks shallower than it is.
  5. 05Total Internal Reflection & Optical FibresPast a certain angle, glass becomes a perfect mirror, and that is how fibres carry light.
  6. 06The Prism & Minimum DeviationA prism bends light by an amount that is smallest when the ray passes through symmetrically.
  7. 07Refraction at a Curved SurfaceThe single curved boundary that lenses, eyes and fish bowls are built from.
  8. 08Thin Lenses & the Lens Maker's FormulaTwo curved surfaces close together: how their curvatures set a lens's focal length.
  9. 09Images by Lenses & MagnificationThree easy rays and one ratio describe every image a single lens can make.
  10. 10Power & Lens CombinationsAdd powers for lenses in contact; account for the gap when they're apart.
  11. 11Defects of Images (Aberrations)Real mirrors and lenses blur, smear and colour their images; designers fight back.
Chapter 19

Optical Instruments

The eye, and the lenses we add to it to see the very small, the very far and the slightly blurred.

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  1. 01The Eye & Apparent SizeA self-focusing camera, and why things look bigger when they're closer.
  2. 02The Simple Microscope (Magnifier)A short-focus lens lets you hold things closer than your eye could manage.
  3. 03The Compound MicroscopeTwo lenses, two stages of magnification, multiplied.
  4. 04TelescopesA long-focus objective brings the far away close; three ways to then look at it.
  5. 05Resolving PowerMagnification is useless past a point: what matters is how fine a detail can be separated.
  6. 06Defects of Vision & SpectaclesWhy some eyes blur the distance or the page, and the lens that fixes each.
Chapter 20

Dispersion & Spectra

Splitting white light into colours, and reading what the colours say about their source.

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  1. 01Dispersion of LightGlass bends violet more than red, and a prism fans white light into a spectrum.
  2. 02Angular Dispersion & Dispersive PowerHow much a material spreads the colours compared with how much it bends them.
  3. 03Combining PrismsTwo prisms of different glass can spread colours without bending the beam, or bend it without spreading.
  4. 04Kinds of SpectraHot solids glow in all colours; gases glow in a few; and missing colours tell what light passed through.
  5. 05The SpectrometerA precise protractor for light: measure the prism angle, minimum deviation and μ for each colour.
  6. 06The RainbowEvery raindrop is a tiny prism and mirror; the bow is a cone of angles around your shadow.
Chapter 21

Speed of Light

How people timed the fastest thing there is.

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  1. 01A Constant Worth MeasuringFrom lanterns on hills to a constant fixed by definition.
  2. 02Fizeau's Toothed WheelChop light into pulses, send them to a far mirror, and spin until the returning light hits a tooth.
  3. 03Foucault's & Michelson's Rotating MirrorsA spinning mirror turns a tiny time delay into a measurable angle.
Chapter 22

Photometry

Measuring light the way the eye experiences it.

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  1. 01Radiant & Luminous FluxWatts measure energy; lumens measure how bright that energy looks.
  2. 02Luminous Efficiency & IntensityHow efficiently a lamp makes light, and how much it sends in each direction.
  3. 03Illuminance & the Lighting LawsHalf as far means four times as bright; tilt the page and it dims.
  4. 04PhotometersMake two screens equally bright and the distances tell you which lamp is stronger.

Heat & Thermodynamics

Temperature, kinetic theory, calorimetry, the laws of thermodynamics and heat transfer.

Chapter 23

Heat & Temperature

What 'hot' means, how to put a number on it, and why things grow when they warm.

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  1. 01Heat, Equilibrium & the Zeroth LawEnergy that flows on its own from hot to cold, and the law that lets us define temperature.
  2. 02Temperature Scales & ThermometersPick a property that changes with temperature, two fixed points, and a straight line between.
  3. 03Gas Thermometers & the Kelvin ScaleGases agree with each other at low pressure, and give a scale independent of any one substance.
  4. 04Thermal ExpansionMost things grow a little when warmed; water near freezing does the opposite.
Chapter 24

Kinetic Theory of Gases

Pressure, temperature and the gas laws from countless tiny collisions.

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  1. 01The Kinetic ModelA gas as a swarm of tiny, fast, elastic molecules.
  2. 02Pressure from MoleculesAdd up the momentum delivered by every molecule bouncing off a wall.
  3. 03Temperature & Molecular SpeedTemperature measures the average kinetic energy of the molecules.
  4. 04The Gas Laws from Kinetic TheoryFive experimental laws, all following from one equation.
  5. 05Speed Distribution, Real Gases & Brownian MotionNot every molecule has the average speed, not every gas is ideal, and pollen grains prove it all.
  6. 06Vapour, Evaporation & BoilingWhen attraction wins: liquefaction, evaporation, and why water boils at 100°C only at sea level.
  7. 07Humidity, Dew & Phase DiagramsHow much water the air holds, and the map of solid, liquid and vapour.
Chapter 25

Calorimetry

Measuring heat: specific heats, latent heats, and the exchange rate between calories and joules.

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  1. 01Heat, Units & the CalorimeterWhat we're measuring, in which units, and the one rule that does the measuring.
  2. 02Specific Heat CapacityWhy iron heats up nine times faster than water, and how to measure it.
  3. 03Latent HeatHeat that changes the phase instead of the temperature.
  4. 04The Mechanical Equivalent of HeatWarming water by friction alone shows a calorie is 4.186 joules.
Chapter 26

Laws of Thermodynamics

Energy is conserved; usefulness is not. Engines, entropy and the limits nature sets.

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  1. 01The First LawHeat in equals internal energy gained plus work done.
  2. 02Work Done by a GasOn a p–V graph, work is an area.
  3. 03Heat EnginesMachines that turn heat into work, and how well they do it.
  4. 04The Second Law & ReversibilityWhy some processes happen and their reverses never do.
  5. 05EntropyA quantity that can be created but never destroyed.
  6. 06The Carnot Engine & RefrigeratorsThe best engine nature allows, and the same machine run backwards.
Chapter 27

Specific Heats of Gases

Why gases have two heat capacities, and how molecular shape predicts them.

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  1. 01Two Heat CapacitiesFor a gas, 'heat per degree' depends on how you heat it.
  2. 02Cp − Cv = RThe extra heat at constant pressure pays for the work of expansion.
  3. 03Measuring Cp and CvA long stream of gas for Cp; a delicate steam balance for Cv.
  4. 04Isothermal & Adiabatic ProcessesSlow and in contact, or fast and insulated: the two limits of a gas process.
  5. 05Equipartition of Energy½kT for every way a molecule can store energy.
Chapter 28

Heat Transfer

Conduction, convection and radiation: the three ways heat gets from here to there.

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  1. 01ConductionHeat passed from molecule to molecule through a solid.
  2. 02Thermal Resistance: Series & ParallelHeat flow does circuit arithmetic.
  3. 03Measuring K & ConvectionA lab measurement of K, and heat that rides along with moving fluid.
  4. 04Radiation, Blackbodies & Kirchhoff's LawGood absorbers are good emitters, and a hole in a box is nearly perfect at both.
  5. 05Wien's & Stefan's LawsHotter bodies glow bluer and radiate far more.
  6. 06Newton's Law of Cooling & Radiation DetectorsCooling slows as a body nears room temperature; how to detect radiation.

Electricity

Electric fields and potential, Gauss's law, capacitors, circuits and the effects of current.

Chapter 29

Electric Field & Potential

Charge, Coulomb's law, and the fields and potentials charges create.

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  1. 01Electric ChargeThe property behind a force 10³⁶ times stronger than gravity.
  2. 02Coulomb's LawThe inverse-square law of electric force.
  3. 03The Electric Field & Field LinesCharges fill space with a field that pushes on other charges.
  4. 04Electric Potential EnergyThe energy stored in an arrangement of charges.
  5. 05Electric PotentialOne number at every point that encodes the whole field.
  6. 06Field from Potential & EquipotentialsIntegrate E to get V; differentiate V to get E.
  7. 07The Electric DipoleA pair of opposite charges: its field, and how it twists in a field.
  8. 08Conductors, Insulators & SemiconductorsFree electrons make the difference, and they empty a conductor of field.
Chapter 30

Gauss's Law

The flux through a closed surface counts the charge inside.

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  1. 01Electric FluxHow much field passes through a surface.
  2. 02Solid AngleThe three-dimensional version of an angle.
  3. 03Gauss's LawTotal flux out of any closed surface = enclosed charge / ε₀.
  4. 04Fields from SymmetrySphere, line and sheet fields in two lines each.
  5. 05Charged Shells & SpheresPoint-charge outside, special inside; and the energy to assemble them.
  6. 06Conductors & EarthingZero field inside metal pushes all charge to the surface.
Chapter 31

Capacitors

Storing charge and energy between two conductors.

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  1. 01Capacitance & Parallel PlatesTwo conductors, equal and opposite charges, and Q = CV.
  2. 02Spherical & Cylindrical CapacitorsCurved plates, and the limits that connect them.
  3. 03Series & Parallel CombinationsSame charge in series, same voltage in parallel.
  4. 04Force & Stored EnergyThe plates pull together; the energy lives in the field.
  5. 05Dielectrics & PolarizationInsulators polarize, and their bound charge weakens the field.
  6. 06Capacitors with DielectricsA slab multiplies C by K, and Gauss's law gets a new form.
  7. 07Corona Discharge & the Van de GraaffSharp points make strong fields; a dome collects charge to millions of volts.
Chapter 32

Electric Current in Conductors

Moving charge, resistance and the circuits built from them.

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  1. 01Electric Current & Current DensityCharge on the move, and how it spreads over a cross-section.
  2. 02Drift Speed of ElectronsFast random motion, slow steady drift.
  3. 03Ohm's Law & ResistanceCurrent density proportional to field; V = Ri.
  4. 04Resistivity & TemperatureMetals resist more when hot; semiconductors less; superconductors not at all.
  5. 05Emf, Heating & Internal ResistanceBatteries pump charge; resistors turn the work into heat.
  6. 06Kirchhoff's LawsConservation of charge and energy, applied to circuits.
  7. 07Series, Parallel & Grouped CellsR adds in series, 1/R in parallel; cells combine too.
  8. 08Wheatstone Bridge, Ammeters & VoltmetersMeasuring resistance by a null, and meters that disturb little.
  9. 09The PotentiometerA voltmeter that draws no current.
  10. 10Charging & Discharging CapacitorsExponential filling and emptying, paced by CR.
  11. 11Atmospheric ElectricityThe planet as a leaky capacitor charged by storms.
Chapter 33

Thermal & Chemical Effects of Current

Currents that heat, pump heat, and move matter.

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  1. 01Joule's Laws of HeatingHeat ∝ i², ∝ t, ∝ R.
  2. 02The Seebeck Effect & ThermocouplesHeat a junction, get a current.
  3. 03Peltier & Thomson EffectsCurrents that pump heat at junctions and along wires.
  4. 04Electrolysis & Faraday's LawsIons carry the current and deposit matter.
  5. 05Primary & Secondary CellsChemistry driving a current, and recharging it.

Magnetism & Electromagnetism

Magnetic fields and forces, magnets and materials, induction, AC circuits and electromagnetic waves.

Chapter 34

Magnetic Field

A field that pushes only on moving charges.

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  1. 01The Magnetic ForceMoving charges feel a sideways push.
  2. 02Circles & HelicesBent into circles, never sped up.
  3. 03Force on a Current-Carrying WireCurrents are pushed by fields.
  4. 04Torque on a Current LoopLoops twist to line up with the field.
Chapter 35

Magnetic Field due to a Current

How currents make magnetic fields.

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  1. 01The Biot–Savart LawEvery current element makes a little field.
  2. 02Force Between Parallel CurrentsLike currents attract; opposite currents repel.
  3. 03Field of a Circular LoopThe loop that behaves like a magnet.
  4. 04Ampère's LawCirculation of B counts the current inside.
  5. 05Solenoids & ToroidsUniform fields from coils.
Chapter 36

Permanent Magnets

Poles, bar magnets, the Earth's field and the instruments that measure them.

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  1. 01Poles & Bar MagnetsMagnets pictured as pairs of magnetic charges.
  2. 02The Field of a Bar MagnetTwo poles, two simple positions, one general formula.
  3. 03Earth's MagnetismThe planet as a tilted bar magnet.
  4. 04GalvanometersMeasuring current with a compass or a twisting coil.
  5. 05MagnetometersM/B_H from deflection, MB_H from oscillation.
  6. 06Gauss's Law for MagnetismMagnetic field lines never start or end.
Chapter 37

Magnetic Properties of Matter

How materials respond to magnetic fields.

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  1. 01Magnetization & Magnetic MaterialsEvery atom a tiny magnet, and three ways matter responds.
  2. 02H, Susceptibility & PermeabilitySeparating the field you apply from the field matter adds.
  3. 03Curie's Law & the Three FamiliesHeat weakens magnetism; ferromagnets switch off above T_c.
  4. 04Hysteresis, Soft Iron & SteelFerromagnets remember their history.
Chapter 38

Electromagnetic Induction

Changing magnetic flux makes emf.

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  1. 01Faraday's & Lenz's LawsChanging flux, induced emf, and the direction it takes.
  2. 02Motional EMFA moving conductor becomes a battery.
  3. 03Induced Electric Field & Eddy CurrentsA changing B makes a curly E.
  4. 04Self-InductionCoils resist changes in their own current.
  5. 05LR Circuits & Magnetic EnergyInductors give circuits inertia and store energy.
  6. 06Mutual Induction & the Induction CoilOne circuit's changing current drives another.
Chapter 39

Alternating Current

Currents that swing back and forth, and the machines that make and use them.

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  1. 01AC & the GeneratorA spinning coil makes alternating emf.
  2. 02RMS ValuesThe size of a current that averages to zero.
  3. 03Resistors, Capacitors & Inductors on ACEach element limits and shifts the current differently.
  4. 04LCR Circuits & ResonanceVector bookkeeping, resonance and tuning.
  5. 05Power, Choke Coils & Hot-Wire MetersOnly the in-phase part of the current does work.
  6. 06Dynamos, Motors & TransformersMaking, using and shipping electrical power.
Chapter 40

Electromagnetic Waves

Light as travelling electric and magnetic fields.

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  1. 01Displacement CurrentA changing electric field makes a magnetic field.
  2. 02Maxwell's Equations & EM WavesFour equations, and light falls out.
  3. 03Energy, Intensity & Radiation PressureLight carries energy and pushes.
  4. 04The EM Spectrum & the AtmosphereOne kind of wave over a vast range of wavelengths.

Modern Physics

Discharges, photons, atoms, X-rays, semiconductors, the nucleus and special relativity.

Chapter 41

Electric Current through Gases

Glowing tubes, cathode rays, the electron, and vacuum valves.

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  1. 01Discharge Through GasesHow a gas at low pressure lights up and conducts.
  2. 02Cathode Rays & Canal RaysInvisible beams of electrons and ions.
  3. 03Measuring the Electron: e/m and eCrossed fields and floating drops measure the electron.
  4. 04Thermionic Emission & the DiodeHot cathodes and one-way valves.
  5. 05The Triode & AmplificationA grid that controls a big current.
Chapter 42

Photoelectric Effect & Wave–Particle Duality

Light as particles, and particles as waves.

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  1. 01PhotonsLight arrives in packets.
  2. 02The Photoelectric EffectSingle photons free single electrons.
  3. 03Matter WavesElectrons diffract too.
Chapter 43

Bohr's Model & Physics of the Atom

From the nuclear atom to quantum states and lasers.

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  1. 01Atomic Models & the NucleusHow alpha particles revealed the nucleus.
  2. 02The Hydrogen SpectrumSharp lines that classical physics couldn't explain.
  3. 03Bohr's ModelQuantized orbits and quantized light.
  4. 04The Quantum AtomProbability clouds instead of orbits.
  5. 05The LaserLight amplified by copying photons.
Chapter 44

X-rays

Radiation that sees through flesh and maps atoms.

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  1. 01Producing X-rays & Their SpectrumBraking radiation plus fingerprint lines.
  2. 02Moseley's LawAtomic number is nuclear charge.
  3. 03Bragg's Law & Uses of X-raysCrystals as gratings; X-rays at work.
Chapter 45

Semiconductors & Semiconductor Devices

From energy bands to logic gates.

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  1. 01Energy Bands in SolidsWhy silicon sits between copper and quartz.
  2. 02Holes, Doping & ConductivityTwo kinds of carrier, and how to choose one.
  3. 03The p-n Junction & DiodesA one-way valve for current.
  4. 04RectifiersTurning AC into one-way current.
  5. 05Junction TransistorsA small current controlling a large one.
  6. 06Logic Gates & Binary AddersComputing with 0s and 1s.
Chapter 46

The Nucleus

Binding, decay, fission and fusion.

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  1. 01Inside the NucleusTiny, dense and held by a short-range force.
  2. 02Binding EnergyWhy nuclei weigh less than their parts.
  3. 03Alpha, Beta & Gamma DecayHow unstable nuclei change.
  4. 04The Law of Radioactive DecayRandom nuclei, predictable samples.
  5. 05Nuclear Fission & ReactorsSplitting atoms, steadily.
  6. 06Nuclear FusionThe power source of the stars.
Chapter 47

The Special Theory of Relativity

Two postulates that reshape space and time.

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  1. 01The Postulates of RelativitySame laws, same light speed, for everyone.
  2. 02Time DilationMoving clocks tick slowly.
  3. 03Length Contraction & SimultaneityShorter rods and disagreeing clocks.
  4. 04Momentum, Mass & EnergyE = mc² and the cosmic speed limit.
  5. 05The Twin ParadoxWho comes home younger, and why.