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B. The particulate nature of matter

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  1. B.1 Thermal energy transfers

    1. B.1.1—Molecular states

      • Describe solids, liquids and gases using molecular theory.

    2. B.1.2—Density

      • Density: ρ=m/V.

    3. B.1.3—Temperature scales

      • Use Kelvin and Celsius temperature scales.

    4. B.1.4—Temperature scale changes

      • Temperature change has the same size in Kelvin and Celsius.

    5. B.1.5—Kelvin temperature and kinetic energy

      • Kelvin temperature measures average particle kinetic energy: Ek=3/2 kBT.

    6. B.1.6—Internal energy

      • Internal energy = intermolecular potential energy + random molecular kinetic energy.

    7. B.1.7—Thermal transfer direction

      • Temperature difference sets the net direction of thermal energy transfer.

    8. B.1.8—Phase change

      • Phase change changes particle behaviour via energy transfer at constant temperature.

    9. B.1.9—Specific heat and latent heat

      • Use Q=mcΔT for temperature change and Q=mL for phase change.

    10. B.1.10—Thermal transfer mechanisms

      • Conduction, convection and thermal radiation are the primary mechanisms for thermal energy transfer.

    11. B.1.11—Conduction

      • Conduction: the difference in the kinetic energy of particles.

    12. B.1.12—Conduction rate

      • Conduction rate depends on material, area and temperature gradient: ΔQ/Δt = kAΔT/Δx.

    13. B.1.13—Convection

      • Qualitative description of thermal energy transferred by convection due to fluid density differences.

    14. 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.

    15. B.1.15—Apparent brightness

      • Concept of apparent brightness b.

    16. B.1.16—Luminosity and brightness

      • Apparent brightness relation: b = L/(4πd^2).

    17. 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.

  2. B.2 Greenhouse effect

    1. B.2.1—Conservation of energy

      • Conservation of energy.

    2. B.2.2—Emissivity

      • Emissivity compares surface radiation per unit area with a black body: ε = power/(σT^4).

    3. B.2.3—Albedo

      • Albedo = total scattered power / total incident power.

    4. B.2.4—Earth’s albedo variation

      • Earth’s albedo varies daily with cloud formation and latitude.

    5. B.2.5—Solar constant S

      • Solar constant S.

    6. B.2.6—Mean solar intensity

      • Mean incoming solar intensity is S/4 due to planetary geometry.

    7. 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.

    8. B.2.8—Infrared absorption

      • Greenhouse gases absorb IR via molecular energy levels. • Radiation is re-emitted in all directions.

    9. B.2.9—Greenhouse models

      • Explain greenhouse effect using resonance and molecular energy-level models.

    10. B.2.10—Enhanced greenhouse effect

      • Enhanced greenhouse effect = augmentation due to human activity.

  3. B.3 Gas laws

    1. B.3.1—Pressure

      • Pressure: P=F/A for force perpendicular to a surface.

    2. B.3.2—Amount of substance

      • Amount of substance: n=N/NA.

    3. B.3.3—Ideal gas model

      • Ideal gases are kinetic-theory models that approximate real gas behaviour.

    4. B.3.4—Empirical gas laws

      • Empirical gas laws combine to PV/T = constant.

    5. B.3.5—Ideal gas equations

      • Ideal gas equations: PV=NkBT and PV=nRT.

    6. 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.

    7. B.3.7—Ideal gas internal energy

      • Internal energy of ideal monatomic gas: U=3/2 NkBT = 3/2 nRT.

    8. B.3.8—Ideal gas approximation limits

      • State temperature, pressure and density conditions for ideal-gas approximation.

  4. B.5 Current and circuits

    1. B.5.1—Cells provide a source of emf

      • Cells provide a source of emf.

    2. 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.

    3. 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.

    4. 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.

    5. B.5.5—Electrical power

      • Electrical power: P=IV=I^2R=V^2/R.

    6. 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.

    7. B.5.7—Electric cells

      • Cells convert chemical energy to electrical energy.

    8. 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.

    9. 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.

    10. 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.

    11. 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.

    12. B.5.12—Resistance and resistivity

      • Resistance depends on resistivity and dimensions: R=ρL/A.

    13. 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.

    14. B.5.14—Emf and internal resistance

      • Cell emf with internal resistance: ε = I(R+r).

    15. B.5.15—Variable resistance

      • Resistors can have variable resistance. • Variable resistors are limited to thermistors, light-dependent resistors (LDRs) and potentiometers.