⚡️College Physics III – Thermodynamics, Electricity, and Magnetism Unit 1 – Temperature and Heat

Key Concepts and Definitions

• Temperature measures the average kinetic energy of particles in a substance
• Heat is the transfer of thermal energy from a hotter object to a cooler one
• Thermal equilibrium occurs when two objects in contact reach the same temperature
• Specific heat capacity is the amount of heat required to raise the temperature of 1 gram of a substance by 1 degree Celsius
• Latent heat is the energy absorbed or released during a phase change without a change in temperature
  • Latent heat of fusion is the energy required to change a substance from solid to liquid (melting ice)
  • Latent heat of vaporization is the energy required to change a substance from liquid to gas (boiling water)
• Thermal expansion is the increase in volume of a substance as its temperature increases (railroad tracks expanding in summer)
• Thermal conductivity measures a material's ability to conduct heat (copper vs. wood)

Temperature Scales and Measurement

• Celsius scale defines 0°C as the freezing point of water and 100°C as the boiling point at standard atmospheric pressure
• Fahrenheit scale defines 32°F as the freezing point of water and 212°F as the boiling point at standard atmospheric pressure
• Kelvin scale is an absolute temperature scale with 0 K representing the lowest possible temperature (absolute zero)
  • Kelvin scale is related to Celsius by: $K = °C + 273.15$
• Temperature can be measured using various devices such as thermometers, thermocouples, and infrared cameras
• Thermometers use the principle of thermal expansion of liquids (mercury or alcohol) to measure temperature
• Thermocouples measure temperature based on the Seebeck effect, which produces a voltage when two dissimilar metals are joined and exposed to different temperatures
• Infrared cameras detect the infrared radiation emitted by objects to determine their temperature (thermal imaging)

Heat and Energy Transfer

• Heat always flows from a region of higher temperature to a region of lower temperature
• Conduction is the transfer of heat through direct contact between particles (touching a hot stove)
  • Rate of conduction depends on the temperature gradient, cross-sectional area, and thermal conductivity of the material
• Convection is the transfer of heat by the movement of fluids or gases (hot air rising)
  • Natural convection occurs due to density differences caused by temperature variations (lava lamps)
  • Forced convection involves an external force, such as a fan or pump, to move the fluid (air conditioning)
• Radiation is the transfer of heat through electromagnetic waves (feeling warmth from the sun)
  • All objects emit thermal radiation based on their temperature and emissivity
• Insulation reduces heat transfer by minimizing conduction, convection, and radiation (fiberglass in walls)
• Heat capacity is the amount of heat required to raise the temperature of an object by a certain amount $Q = mc\Delta T$

Thermal Properties of Matter

• Thermal expansion occurs in solids, liquids, and gases as temperature increases
  • Linear expansion is the change in length of a solid $\Delta L = \alpha L_0 \Delta T$
  • Volumetric expansion is the change in volume of a substance $\Delta V = \beta V_0 \Delta T$
• Specific heat capacity varies among different materials (water has a high specific heat capacity compared to sand)
• Phase changes occur at specific temperatures and involve latent heat (melting, freezing, vaporization, condensation)
• Thermal conductivity is a measure of a material's ability to conduct heat (metals have high thermal conductivity)
• Thermal resistance is the inverse of thermal conductivity and measures a material's ability to resist heat flow (insulation has high thermal resistance)
• Thermal diffusivity is the ratio of thermal conductivity to the product of density and specific heat capacity, and it measures the rate at which heat spreads through a material (heat spreads faster in copper than in wood)

Laws of Thermodynamics

• Zeroth Law: If two systems are in thermal equilibrium with a third system, they are in thermal equilibrium with each other
• First Law: Energy cannot be created or destroyed, only converted from one form to another $\Delta U = Q - W$
  • In a closed system, the change in internal energy is equal to the heat added minus the work done by the system
• Second Law: The total entropy of an isolated system always increases over time
  • Heat cannot spontaneously flow from a colder body to a hotter body
  • It is impossible to have a process that converts heat completely into work without any other changes (100% efficient engine is impossible)
• Third Law: As the temperature of a system approaches absolute zero, its entropy approaches a constant minimum value
  • It is impossible to reach absolute zero in a finite number of steps

Applications in Daily Life and Technology

• Thermometers are used to measure body temperature and environmental temperature (medical and weather applications)
• Refrigerators and air conditioners use the principles of heat transfer and phase changes to cool spaces (removing heat from inside and releasing it outside)
• Insulation in buildings and clothing helps to maintain a comfortable temperature by reducing heat transfer (fiberglass, foam, and down feathers)
• Heat engines, such as internal combustion engines and steam turbines, convert heat into mechanical work (cars and power plants)
• Solar panels use the principle of thermal radiation to convert sunlight into electricity (photovoltaic cells)
• Heat exchangers are used in various industrial processes to transfer heat between fluids (radiators in cars and heat sinks in electronics)

Problem-Solving Techniques

• Identify the relevant concepts and principles related to the problem (heat transfer, thermal properties, laws of thermodynamics)
• Determine the given information and the unknown quantities to be found
• Select the appropriate equations or formulas to solve the problem (heat transfer equations, thermal expansion formulas)
• Substitute the given values into the equations and solve for the unknown quantities
• Check the units and the reasonableness of the answer (does the result make sense in the context of the problem?)
• Consider any assumptions made and the limitations of the models used (ideal gas law, constant specific heat capacity)

Connections to Other Physics Topics

• Thermodynamics is closely related to the study of energy and its transformations (mechanical, electrical, and chemical energy)
• The kinetic theory of gases connects the microscopic behavior of particles to the macroscopic properties of gases (pressure, volume, and temperature)
• Heat engines and refrigerators are examples of the application of thermodynamics to mechanical systems (work, efficiency, and power)
• The study of phase changes and latent heat is related to the concepts of intermolecular forces and bonding (solid, liquid, and gas phases)
• Thermal radiation is a form of electromagnetic radiation, which is also studied in optics and modern physics (blackbody radiation and the photoelectric effect)
• The concept of entropy is related to the study of statistical mechanics and the behavior of large systems of particles (microstates and macrostates)