Physics Chapter on Temperature and Heat Transfer

Temperature and Thermal Equilibrium

• Temperature is a measure of the average kinetic energy of the particles in a substance.
• Heat is energy transferred from a hotter object to a colder object due to a temperature difference.
• Thermal equilibrium occurs when two objects in contact have the same temperature, and no further heat transfer happens.
• Temperature is measured in degrees Celsius (°C) or Kelvin (K). Kelvin is an absolute scale, where 0 K is absolute zero (no kinetic energy).
• The relationship between Celsius and Kelvin is K = °C + 273.15

Specific Heat Capacity

• Specific heat capacity is the amount of heat required to raise the temperature of 1 kg of a substance by 1°C.
• It is a property of a substance.
• Larger specific heat capacity means a substance can absorb more heat for a given temperature change.
• The formula is: ΔQ = mcΔT, where ΔQ is the heat transferred, m is the mass, c is the specific heat capacity, and ΔT is the change in temperature.

Latent Heat

• Latent heat is the amount of heat energy required to change the state of a substance without changing its temperature.
• Latent heat of fusion is the energy required to change a substance from solid to liquid at its melting point.
• Latent heat of vaporisation is the energy required to change a substance from liquid to gas at its boiling point.
• Latent heat is also associated with changes in state. The heat absorbed or released does not involve a temperature change.

Thermal Expansion

• Materials expand when heated and contract when cooled.
• Linear expansion: change in length is proportional to the change in temperature.
• Volume expansion: change in volume is proportional to the change in temperature.
• Expansion coefficients quantify how much a substance expands or contracts with temperature changes. These coefficients differ significantly between substances.

Conduction

• Conduction is the transfer of thermal energy through a material (or between materials in contact) without the bulk movement of the material itself.
• It involves the transfer of kinetic energy between particles, often via molecular vibrations.
• Good conductors have free electrons that readily transfer heat energy.
• Poor conductors, or insulators, impede heat transfer.
• Factors affecting rate of conduction include thickness of material, material's thermal conductivity, and temperature difference.

Convection

• Convection is the transfer of thermal energy by the bulk movement of a fluid (liquid or gas).
• Heated fluids expand, become less dense, and rise.
• Cooler, denser fluids sink, creating a convection current.
• Convection currents are responsible for many natural phenomena, such as weather patterns, and the movement of heat in liquids and gases.
• Convection currents transfer heat more efficiently in fluids than conduction.

Radiation

• Radiation is the transfer of thermal energy in the form of electromagnetic waves.
• All objects emit and absorb radiation.
• The rate of emission and absorption depends on the object's temperature and surface properties.
• Black surfaces absorb and emit radiation more effectively than bright, shiny surfaces.
• Radiation is the primary method of heat transfer in vacuum, where conduction and convection are not possible.

Greenhouse Effect

• The Earth's atmosphere traps some of the Sun's outgoing radiation, keeping the planet warmer.
• Gases in the atmosphere, such as carbon dioxide and water vapor, absorb and re-emit infrared radiation, leading to the greenhouse effect.
• An increase in greenhouse gases can lead to an enhanced greenhouse effect, resulting in global warming.

Specific Latent Heat and Examples

• Latent heat of fusion: Water. Ice changing to water at 0°C, absorbing heat but not getting warmer.
• Latent heat of vaporization: Water. Water changing to steam at 100°C, absorbing heat but not getting warmer.
• It also relates to processes like melting ice or boiling water, and the energy required for these changes.

Practical Applications of Thermal Physics Principles

• Designing efficient insulation for buildings or homes.
• Analyzing how materials are affected by heat and temperature change in engineering contexts.
• Understanding and managing processes requiring the specific heat or latent heat in industrial settings.
• Designing ovens for cooking or furnaces for heat transfer.
• Understanding and predicting weather patterns.