Physics Notes: Atoms and Heat Concepts

Introduction to Atoms and Heat

  • Fundamental Particles:

    • Protons: Positively charged
    • Neutrons: Neutral charge
    • Electrons: Negatively charged

  • Atoms:

    • Fundamental building blocks of matter.

Structure of Matter

  • Leptons and Baryons:
    • Leptons: Indivisible particles, including electrons.
    • Baryons: Composed of quarks.
    • Proton: 3 quarks
    • Neutron: 3 quarks
    • Mesons: 2 quarks

Heat and Temperature

  • Definition of Heat:
    • Experienced due to molecular and atomistic movement and vibrations.
  • Measurement of Heat:
    • Measured in:
    • Kelvin (K)
    • Degrees Celsius (°C)
    • Degrees Fahrenheit (°F)
    • 0K: Absolute zero where molecular motion stops.
  • Elements and Atoms:
    • Composed of protons, neutrons, and electrons that form specific materials.
    • Atomic Number: Number of protons.
    • Atomic Symbol: Represents the element.
    • Atomic Mass: Number of protons + neutrons.

Phases of Matter

  • States of Matter:
    • Solid
    • Liquid
    • Gas
    • Plasma
  • Energy and Phase Changes:
    • Adding heat causes molecular vibrations leading to phase changes (e.g. water from solid to liquid to gas).

Temperature Measured

  • Temperature Scale:

    • Kelvin (K): Absolute scale.
    • Degrees Celsius (°C): Water freezing/boiling point reference.
    • Degrees Fahrenheit (°F): Generally used in the US.

  • Temperature Conversion Formulas:

    • TC = T{K} - 273.15
    • TF = rac{9}{5}TC + 32

  • Example: Room temperature is 68°F = 20°C = 298K

Heat Transfer Methods

  • Conduction:
    • Transfer of energy through direct contact (e.g., heating air directly from a heater.)
  • Convection:
    • Energy carried by moving material (e.g., warm air rising and circulating.)
  • Radiation:
    • Energy transmitted through space by electromagnetic waves (e.g., warmth from sunlight.).

Thermal Expansion and Contraction

  • Thermal Expansion:
    • As temperature increases, materials expand, becoming less dense.
  • Thermal Contraction:
    • As temperature decreases, materials contract, becoming more dense.
  • Example: Concrete sidewalks expand in summer and contract in winter, leading to cracks over time.

Thermometers

  • How Thermometers Work:
    • Use thermal expansion; liquid expands as temperature rises, indicating temperature on a scale.

Speed of Sound

  • Factors Influencing Speed:
    • Dependent on temperature and medium density.
    • Speed of sound in air: ~700 mph or ~340 m/s or ~1000 ft/s.
  • Comparison with Speed of Light:
    • Speed of light: 3 imes 10^8 m/s or 186,000 miles/s.
    • Lightning is seen before thunder due to the difference in speed.

Ideal Gas Law

  • Basic Equation:
    • P1V1 = P2V2
    • rac{V1}{T1} = rac{V2}{T2}
    • rac{P1}{T1} = rac{P2}{T2}
  • Gas Behavior:
    • As temperature increases, volume/pressure can increase; pressure decreases, temperature decreases; pressure increases, volume decreases.

Heat Engines

  • Types of Heat Engines:
    • Combustion Engine: Burns gasoline/air to produce energy.
    • Steam Engine: Uses steam to power turbines.
  • Efficiency:
    • Efficiency = 1 - rac{T{cold}}{T{hot}}
    • For example, with T{hot} = 1000 K and T{cold} = 700 K, efficiency is 1 - (700/1000) = 0.3 or 30%.

Refrigerators and Heat Pumps

  • Functionality:
    • Operate based on temperature changes when a gas expands/condenses.
    • In refrigerators, the evaporator cools the interior; in heat pumps, it heats.

Laws of Thermodynamics

  • Zeroth Law:
    • Objects in contact reach the same temperature.
  • First Law:
    • Energy is conserved (including heat).
  • Second Law:
    • Heat energy cannot be extracted without a temperature difference.
  • Third Law:
    • Nothing can reach absolute zero (0 K).

Entropy

  • Definition:
    • Quantifies disorder; higher disorder equals higher entropy.
  • Entropy Change Equation:
    • ext{Total change in } S = rac{Q}{Tc} - rac{Q}{TH}
  • Observations About Entropy:
    • The entropy of the universe tends to increase.
    • Cooling of an object decreases entropy, but surrounding heating can increase total entropy.

Takeaways on Atoms and Heat

  • The movement of atoms creates both heat and temperature.
  • Key processes include conduction, convection, and radiation.
  • Familiarization with Ideal Gas Laws and the laws of thermodynamics is crucial.
  • Understanding the concept of entropy is essential in thermodynamics.