Overview
This lecture covers the forms of energy, energy transfer methods, work and power calculations, and various renewable and non-renewable energy resources used in electricity generation.
Forms of Energy and Their Equations
- Energy is the ability to do work; its unit is Joule (J), a scalar quantity.
- Kinetic energy: ( KE = \frac{1}{2}mv^2 ), where m = mass (kg), v = speed (m/s).
- Gravitational potential energy: ( PE = mgh ), g = 10 m/s², h = height (m).
- Mechanical energy = kinetic + potential energy.
- Elastic, chemical, electrical, and nuclear energies are other forms of stored energy.
- Thermal/heat energy relates to internal energy responsible for temperature.
- Light is radiant electromagnetic energy; sound is energy from particle vibrations.
Conservation of Energy and Efficiency
- Energy cannot be created or destroyed, only transferred between forms.
- Efficiency ( = \frac{\text{useful output energy}}{\text{input energy}} \times 100% ).
- Example efficiencies: light bulb (41.7%), TV (85.5%), electric motor (60%), running person (62.5%).
- Sankey diagrams visually represent proportions of energy transfers and losses.
Methods of Thermal Energy Transfer
- Heat transfers from hot to cold objects until thermal equilibrium.
- Conduction: transfer via particle collisions, fastest in metals due to free electrons; insulators lack free electrons.
- Convection: transfer by movement of fluids (liquids/gases); warm fluid rises, cools, and sinks, creating convection currents.
- Radiation: transfer by electromagnetic waves (infrared); needs no medium.
Experiments Demonstrating Energy Transfer
- Good thermal conductors (e.g., copper) transfer heat quickly; poor conductors (e.g., water, air) do not.
- Matte black surfaces absorb and emit thermal radiation better than shiny white/silver surfaces.
Work, Power, and Energy Calculations
- Work done: ( W = F \times d ), where F = force (N), d = distance (m).
- Work is zero if force is perpendicular to motion.
- The increase in kinetic or potential energy equals the work done on an object.
- Power: ( P = \frac{W}{t} ) or ( \frac{E}{t} ), where t = time (s).
Practical Examples and Energy Transfers
- Energy is lost as heat due to friction or air resistance.
- In systems like pendulums or rolling balls, the sum of kinetic and potential energy (mechanical energy) remains constant if no energy is lost.
Energy Resources and Power Generation
- Non-renewable resources: fossil fuels, nuclear (uranium/plutonium); eventually run out, produce emissions or waste.
- Renewable resources: biomass, geothermal, wind, hydroelectric, tidal, wave, solar; do not run out.
- Each power plant type converts one form of stored energy into electricity, with specific advantages and disadvantages.
Key Terms & Definitions
- Energy — ability to do work (Joule).
- Kinetic Energy — energy from motion ( (\frac{1}{2}mv^2) ).
- Potential Energy — energy from position ( (mgh) ).
- Efficiency — ratio of useful energy output to total input.
- Thermal Equilibrium — state when objects reach the same temperature.
- Conduction — heat transfer through solids by particle vibration.
- Convection — heat transfer in fluids due to density changes.
- Radiation — heat transfer by electromagnetic waves.
- Work — force times distance moved in direction of force.
- Power — rate of work or energy transfer per time (Watt).
Action Items / Next Steps
- Review example calculations for work, energy, and efficiency.
- Study diagrams of power plants and Sankey diagrams.
- Complete assigned problems on energy transfer and resource types.