HL IB Physics - Thermal Energy Transfers

Contents

• Solids, Liquids & Gases
• Density
• Temperature Scales
• Temperature & Kinetic Energy
• Internal Energy
• Thermal Equilibrium
• Changes of State
• Specific Heat Capacity
• Specific Latent Heat
• Thermal Conduction
• Thermal Convection
• Thermal Radiation
• Apparent Brightness & Luminosity
• Stefan-Boltzmann Law
• Wiens Displacement Law

Solids, Liquids & Gases

• States of Matter: solid, liquid, gas
• Kinetic Theory: explains properties of matter
  • Particles as small spheres

Solids

• Particles:
  • Closely packed
  • Arranged in fixed lattice
  • Vibrate in fixed positions
  • Low energies, can't overcome intermolecular forces
• Properties:
  • Fixed shape and volume
  • High density, difficult to compress

Liquids

• Particles:
  • Closely packed, randomly arranged
  • Flow past each other
  • Higher energy than solids
• Properties:
  • No fixed shape, takes container's shape
  • Fixed volume, hard to compress
  • Medium density

Gases

• Particles:
  • Far apart, random arrangement
  • Move freely and collide
  • High energy, can overcome intermolecular forces
• Properties:
  • No fixed shape or volume, fills container
  • Compressible
  • Low density

Density

• Definition: Mass per unit volume
• Units: g/cm³ or kg/m³
• Example: Bucket of feathers vs. sand
• Calculations involve using volume formulas for shapes

Temperature Scales

• Kelvin Scale:
  • Absolute zero: 0 K or -273 °C
  • Conversion: T(K) = T(°C) + 273
  • No negative values in Kelvin

Temperature & Kinetic Energy

• Particles have diverse speeds
• Average kinetic energy: (E_k = \frac{3}{2}k_BT)
  • (k): Boltzmann's constant (1.38 \times 10^{-23} J/K)
  • Proportionality to temperature

Internal Energy

• Definition: Sum of total kinetic and intermolecular potential energy
• With thermal energy change:
  • Increases kinetic and potential energy
  • Temperature change only with kinetic energy change

Thermal Equilibrium

• Energy transfers from hotter to cooler region until equal temperature
• No more heat exchange once equilibrium is reached

Changes of State

• Phase transitions include melting, freezing, boiling, condensation
• Energy Transfer: affects potential, not kinetic energy

Specific Heat Capacity

• Definition: Thermal energy required to change 1 kg of substance by 1 K
• Formula: (Q = mc\Delta T)
• Substances like water have high specific heat capacities

Specific Latent Heat

• Definition: Energy needed to change state of 1 kg without temperature change
• Types:
  • Fusion: solid to liquid
  • Vaporisation: liquid to gas
• Energy required for vaporisation > fusion

Thermal Conduction

• Heat transfer in solids, more effective in metals due to free electrons
• Involves atomic vibrations and electron collisions
• Thermal Conductivity: Substance's ability to conduct heat
  • High in metals, low in insulators
  • Formula: (\frac{Q}{t} = \frac{kA\Delta T}{x})

Thermal Convection

• Movement of fluids due to density changes
• Occurs in liquids and gases, not solids
• Creates convection currents

Thermal Radiation

• Emission of electromagnetic waves, typically in infrared
• Black-body Radiation: Perfect absorber/emitter
• Heat transfer method in vacuum

Apparent Brightness & Luminosity

• Apparent Brightness: Intensity from a star on Earth (b = \frac{L}{4\pi d^2})
• Luminosity: Total power emitted by a star

Stefan-Boltzmann Law

• Power radiated by black body: (P = \sigma AT^4)
• Relates temperature and surface area to power emitted

Wiens Displacement Law

• Peak wavelength inversely proportional to temperature (\lambda_{max} = \frac{b}{T})_

These notes provide a comprehensive overview of key points related to thermal energy transfers, useful as a study aid.