B. The particulate nature of matter
Start with Concept to understand a topic, then use Question Bank to check what you know.
Your progress
Sign in to see your mastery and mistakes.
B.1 Thermal energy transfers
B.1.1—Molecular states
• Describe solids, liquids and gases using molecular theory.
B.1.2—Density
• Density: ρ=m/V.
B.1.3—Temperature scales
• Use Kelvin and Celsius temperature scales.
B.1.4—Temperature scale changes
• Temperature change has the same size in Kelvin and Celsius.
B.1.5—Kelvin temperature and kinetic energy
• Kelvin temperature measures average particle kinetic energy: Ek=3/2 kBT.
B.1.6—Internal energy
• Internal energy = intermolecular potential energy + random molecular kinetic energy.
B.1.7—Thermal transfer direction
• Temperature difference sets the net direction of thermal energy transfer.
B.1.8—Phase change
• Phase change changes particle behaviour via energy transfer at constant temperature.
B.1.9—Specific heat and latent heat
• Use Q=mcΔT for temperature change and Q=mL for phase change.
B.1.10—Thermal transfer mechanisms
• Conduction, convection and thermal radiation are the primary mechanisms for thermal energy transfer.
B.1.11—Conduction
• Conduction: the difference in the kinetic energy of particles.
B.1.12—Conduction rate
• Conduction rate depends on material, area and temperature gradient: ΔQ/Δt = kAΔT/Δx.
B.1.13—Convection
• Qualitative description of thermal energy transferred by convection due to fluid density differences.
B.1.14—Black-body radiation
• Black-body radiation power follows Stefan-Boltzmann law: L=σAT^4. • Applies to emission of electromagnetic waves from a black-body surface.
B.1.15—Apparent brightness
• Concept of apparent brightness b.
B.1.16—Luminosity and brightness
• Apparent brightness relation: b = L/(4πd^2).
B.1.17—Wien’s displacement law
• Use black-body spectrum and Wien’s law: λmaxT = 2.9x10^-3 m K. • Use λmax to infer black-body temperature.
B.2 Greenhouse effect
B.2.1—Conservation of energy
• Conservation of energy.
B.2.2—Emissivity
• Emissivity compares surface radiation per unit area with a black body: ε = power/(σT^4).
B.2.3—Albedo
• Albedo = total scattered power / total incident power.
B.2.4—Earth’s albedo variation
• Earth’s albedo varies daily with cloud formation and latitude.
B.2.5—Solar constant S
• Solar constant S.
B.2.6—Mean solar intensity
• Mean incoming solar intensity is S/4 due to planetary geometry.
B.2.7—Greenhouse gases
• Main greenhouse gases: CH4, H2O, CO2 and N2O from natural and human sources. • Greenhouse gases have both natural and human-created origins.
B.2.8—Infrared absorption
• Greenhouse gases absorb IR via molecular energy levels. • Radiation is re-emitted in all directions.
B.2.9—Greenhouse models
• Explain greenhouse effect using resonance and molecular energy-level models.
B.2.10—Enhanced greenhouse effect
• Enhanced greenhouse effect = augmentation due to human activity.
B.3 Gas laws
B.3.1—Pressure
• Pressure: P=F/A for force perpendicular to a surface.
B.3.2—Amount of substance
• Amount of substance: n=N/NA.
B.3.3—Ideal gas model
• Ideal gases are kinetic-theory models that approximate real gas behaviour.
B.3.4—Empirical gas laws
• Empirical gas laws combine to PV/T = constant.
B.3.5—Ideal gas equations
• Ideal gas equations: PV=NkBT and PV=nRT.
B.3.6—Molecular pressure model
• Pressure arises from molecular momentum changes in collisions with surfaces. • Average translational speed relation: P = 1/3 ρv^2.
B.3.7—Ideal gas internal energy
• Internal energy of ideal monatomic gas: U=3/2 NkBT = 3/2 nRT.
B.3.8—Ideal gas approximation limits
• State temperature, pressure and density conditions for ideal-gas approximation.
B.4 Thermodynamics
B.4.1 (HL)—First law of thermodynamics
• First law for closed systems: Q = ΔU + W.
B.4.2 (HL)—Gas work
• Work done by/on a gas from pressure-volume change: W = PΔV.
B.4.3 (HL)—Internal energy change
• The change in internal energy: ΔU = 3 2 NkBΔT = 3 2nRΔT of a system is related to the change of its temperature.
B.4.4 (HL)—Entropy and disorder
• Entropy relates to microscopic disorder of particles in a system.
B.4.5 (HL)—Entropy equations
• Entropy change: ΔS=ΔQ/T. • Statistical entropy: S=kB ln Ω.
B.4.6 (HL)—Second law of thermodynamics
• Second law: entropy of an isolated system never decreases.
B.4.7 (HL)—Irreversibility
• Real isolated processes are usually irreversible; entropy tends to increase.
B.4.8 (HL)—Local entropy decrease
• Local entropy can decrease in a non-isolated system if surroundings increase more. • Surroundings must increase entropy enough for total entropy to increase.
B.4.9 (HL)—Gas processes
• Know isovolumetric, isobaric, isothermal and adiabatic gas processes. • Processes keep one state variable or heat transfer condition fixed.
B.4.10 (HL)—Adiabatic ideal gas
• Adiabatic monatomic ideal gas: PV^(5/3)=constant.
B.4.11 (HL)—Heat engine cycles
• Cyclic gas processes underpin heat engines.
B.4.12 (HL)—Heat engine efficiency
• Heat engine efficiency: η=W/QH=1-QC/QH.
B.4.13 (HL)—Carnot efficiency limit
• Carnot efficiency limit: ηCarnot = 1 - TC/TH.
B.5 Current and circuits
B.5.1—Cells provide a source of emf
• Cells provide a source of emf.
B.5.2—Electrical energy sources
• Chemical cells and solar cells are energy sources in circuits. • Compare the advantages and disadvantages of different sources of electrical energy.
B.5.3—Resistance
• Explain the properties of electrical conductors and insulators in terms of the mobility of charge carriers. • Explain electrical resistance and its origin. • Use electrical resistance R=V/I.
B.5.4—Ohmic behaviour
• Apply Ohm’s law: for an ohmic metal conductor at constant temperature, V ∝ I. • Distinguish ohmic and non-ohmic behaviour of electrical conductors, including the heating effect of resistors.
B.5.5—Electrical power
• Electrical power: P=IV=I^2R=V^2/R.
B.5.6—Potential difference and electrical energy transfer
• Electric potential difference V is the work done W per unit charge q on moving a positive charge between two points along the path of the current: V=W/q. • Relate electrical energy transfer to power and time: E=Pt=IVt.
B.5.7—Electric cells
• Cells convert chemical energy to electrical energy.
B.5.8—Circuit diagrams and conventional current
• Circuit diagrams represent the arrangement of components in a circuit; use the required electrical circuit symbols provided in the Physics data booklet. • Conventional current follows the direction of positive charge flow. • Treat ammeters and voltmeters as ideal unless stated otherwise; a stated non-ideal meter has constant resistance.
B.5.9—Direct current and charge flow
• Direct current I is a flow of charge carriers in one direction, with I=Δq/Δt. • Alternating-current circuit analysis is not required.
B.5.10—Direct and alternating current boundary
• Distinguish direct current, whose direction does not reverse, from alternating current, whose direction reverses. • This distinction defines the syllabus boundary only; alternating-current circuit analysis is not required.
B.5.11—Conservation in series and parallel circuits
• Use conservation of charge to explain why currents add at a junction in a parallel circuit. • Use conservation of energy to explain why potential differences add in a series circuit. • General multi-loop circuit analysis is not required.
B.5.12—Resistance and resistivity
• Resistance depends on resistivity and dimensions: R=ρL/A.
B.5.13—Series and parallel circuits
• Use series/parallel rules for current, voltage and equivalent resistance. • Series: same current; voltages and resistances add. • Parallel: same voltage; currents add; reciprocal resistance adds.
B.5.14—Emf and internal resistance
• Cell emf with internal resistance: ε = I(R+r).
B.5.15—Variable resistance
• Resistors can have variable resistance. • Variable resistors are limited to thermistors, light-dependent resistors (LDRs) and potentiometers.