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.