Theme B and Theme E Physics (2)
B.1 Thermal Energy Transfers
Thermal Concepts
Temperature and Heat Flow: Heat transfers from hot to cold objects when they are in thermal contact, determined by their temperature difference.
Equilibrium: Objects reach thermal equilibrium when they have the same temperature.
Heat Definition: Heat is not a substance, but the transfer of thermal energy, often measured in calories or joules.
Temperature Scales: Common scales include Celsius (°C) and Kelvin (K). The relationship is T(K) = t(°C) + 273.
Specific Concepts in Gases
Pressure (P): Force exerted per unit area. SI units: Nm⁻² or Pascals (Pa).
Volume (V): Measured in m³ or cm³.
Temperature (t): Measured in °C or K.
Density (p): Calculated as p = m/V, where m is mass in kg and V is volume in m³.
B.2 Heat and Internal Energy
Microscopic vs. Macroscopic Views
Macroscopic: Looks at the system as a whole and how it interacts with its surroundings.
Microscopic: Examines interactions at the atomic and molecular levels.
Internal Energy
An object gains or loses energy as its temperature changes, which can be in kinetic or potential forms.
Total internal energy (U) is the sum of kinetic and potential energy at the molecular level.
Kinetic Theory
States of Matter:
Solids: Fixed volume and shape with particles vibrating in place.
Liquids: Fixed volume but changing shape, particles can move around each other.
Gases: No fixed volume or shape, particles move independently and collide.
B.3 Specific Heat Capacity
Definitions and Measurements
Thermal Capacity (C): Energy required to raise temperature by 1 K; Specific Heat Capacity (c) is energy required to raise 1 kg of a substance by 1 K.
Methods for measuring include:
Electrical method (involving heat input & temperature changes).
Method of mixtures (using known heat capacities and temperature changes).
B.4 Phases of Matter and Latent Heat
Phase Changes
When a substance changes phase (e.g., melting, boiling), temperature remains constant, but thermal energy is absorbed or released.
Specific Latent Heat (L): Energy absorbed/released per unit mass during phase changes.
Measuring Latent Heats
Methods involve calorimetry and calculations using energy balances during phase transitions.
B.5 Thermal Energy Transfer Processes
Conduction
Definition: Heat transfer through matter without any bulk movement.
Mechanism: Kinetic energy transfer through particle collisions.
Materials: Good conductors (metals) vs. insulators (wood, air).
Convection
Definition: Transfer of heat through liquid or gas movement due to density differences.
Example: Warm air rising and cool air sinking creates currents.
Radiation
Definition: Transfer of energy through electromagnetic waves, doesn't require a medium.
Examples: Sun warming Earth, heat from a fire.
B.6 Additional Notes on Thermal Energy
Key Takeaways
Most substances can be modeled with thermal concepts including specific heat, latent heat, and phase changes affecting interactions at the atomic level.
Understanding Radiation Laws
Inverse Square Law: Intensity of radiation drops with the square of the distance from the source, applies to all waves.
Gravitational Fields (D.1)
Key Concepts
Newton’s Law of Gravitation: Describes how every mass attracts every other mass, F = G(m₁m₂)/r².
Gravitational Field Strength (g)
Defined as the force per unit mass (N/kg), varies by distance from mass.
Orbit Dynamics
Kepler’s Laws: Governs orbital motion, including relationships between the orbital period and radius.
Stability and Nuclear Forces
Strong nuclear forces work at very short ranges to keep nucleons together. Weak forces engage with beta decay processes.
Nuclear Stability and Decay
Isotopes stabilize differently; binding energy plays a crucial role in decay processes.
Electric Fields (D.2)
Electric Charge and Forces
Charges produce electric fields; Coulomb's law defines their interactions.
Electric Field Strength (E)
Defined as force on a unit charge (N/C or V/m), represented with field lines indicating direction and intensity.
Electric Potential Energy
Defines energy per charge related to the electric field and is integral in determining work done in moving charges between points in the field.
Quantum Concepts (E.2)
Phenomena of Wave-Particle Duality
Light and matter exhibit both particle-like and wave-like properties captured in phenomena such as the photoelectric effect and Compton scattering.
Matter Waves
De Broglie's hypothesis equates the motion of particles with wave characteristics, influencing calculations for momentum and wavelength.
Radioactivity (E.3)
Types of Radiation
Radioactive decay emits alpha, beta, or gamma radiation, each possessing unique ionizing properties affecting biological structures.
Decay Processes and Chain Reactions
Chain reactions are crucial in nuclear fission processes, often regulated to prevent uncontrolled reactions.
Uses of Radioactivity
Applications in medical diagnostics, treatments, sterilization processes, and illumination of processes such as carbon dating.
Key Calculations
Half-life calculations allow the determination of remaining quantities of radioactive materials, critical in understanding the longevity of isotopes.