Energy, Heat, and Thermodynamics

Posted on Oct 9, 2024 in Physics

Energy

Energy is the capacity of a body to interact with other bodies. Energy is neither created nor destroyed, only transformed. It is measured in Joules (J).

Types of Energy

  • Kinetic Energy: The energy a body possesses due to its motion. Ec = 0.5 * m * v2
  • Potential Energy: The energy a body possesses due to its position.
    • Gravitational Potential Energy: Ep = m * g * h (g = 9.8 m/s2)
    • Elastic Potential Energy: Ep = 0.5 * k * x2 (k = N/m)
  • Mechanical Energy: The sum of kinetic and potential energy.
  • Heat: The energy exchanged between two systems at different temperatures.

Energy Transfer

  • Waves: Radio waves, TV waves, infrared, visible light, ultraviolet radiation, X-rays, gamma rays. Energy increases as frequency and wavelength decrease. E = h * f (h = Planck’s constant = 6.63 * 10-34 J/s, f = frequency (Hz)). c = λ * f (λ = wavelength (m), c = speed of light = 3 * 108 m/s).
  • Contact: Transferring energy by connecting two objects at different temperatures.

Work (W)

Work is a physical quantity that measures the energy transferred from one body to another by applying a force. It is measured in Joules (J).

Force

Force is a physical quantity that measures the interaction between bodies. Forces cause deformations or changes in the motion of bodies. Force is measured in Newtons (N).

Temperature

Temperature is a fundamental physical quantity that measures the average kinetic energy of the particles in a body. It is not defined for individual particles but for the entire material system. It measures the degree of vibration of the particles. Units: Celsius, Fahrenheit, Kelvin (0°C = 273K = 32°F). Measurement: Mercury or digital thermometer.

Internal Energy (U)

Internal energy is a microscopic physical quantity that measures the total mechanical energy of the particles due to their translational and vibrational movements. It is the sum of the mechanical energy of all particles: U = Σ(Ec + Ep).

Heat (Q)

Heat is the amount of energy transferred from one body to another due to a temperature difference. Units: Joules (J), calories (cal). 1 cal = 4.18 J (energy required to raise the temperature of 1g of water by 1°C).

Thermal Equilibrium

When two objects at different temperatures come into contact, there is a transfer of energy from the hotter object to the colder object until they reach the same temperature.

Specific Heat (Ce)

Specific heat is the amount of energy required to raise the temperature of 1 gram of a substance by 1 degree Celsius. It is a characteristic property of each substance. For example, the specific heat of water is 1 cal/g°C.

Mechanical Equivalent of Heat

The mechanical work done on a system can be totally or partially converted into heat, demonstrating the equivalence between work and heat units.

Effects of Heat

  • Physical Changes:
    • Expansion of bodies
    • Increased temperature
    • Change of state:
      • Latent heat of fusion: Energy required for 1 gram of a solid substance to change to a liquid at the same temperature.
      • Latent heat of vaporization: Energy required for 1 gram of a liquid substance to change to a gas at the same temperature.
  • Chemical Changes: Increase in kinetic and potential energy.

Heat Propagation

  • Conduction: Transfer of heat through direct contact between particles.
  • Convection: Transfer of heat through the movement of fluids (liquids and gases).
  • Radiation: Transfer of heat through electromagnetic waves.

Heat Engines

A heat engine is a device that operates cyclically, absorbing heat from a hot source, transforming a portion of that heat into work, and releasing the rest to a cold source.

Types of Heat Engines

  • External Combustion Engine: Uses steam generated outside the engine (e.g., steam engine).
  • Internal Combustion Engine: Uses a combustion reaction within the engine (e.g., spark ignition engine).

Refrigerator

A refrigerator is a heat engine that operates in reverse, transferring heat from a cold source to a hot source.

Thermal Wave

A thermal wave is a disturbance that carries energy from one place to another without transferring mass.

Kilowatt-hour (kWh)

A unit of electrical energy. Power = Joules/second = Watts.

pH

pH indicates the acidity or basicity of a solution. 0-7: acidic, 7: neutral, 7-14: basic.

Indicator

A substance that changes color to indicate whether a solution is acidic or basic (e.g., litmus paper, red cabbage juice, phenolphthalein).