Energy Notes

Energy Transformations and Conservation

  • Energy is neither created nor destroyed; it transforms from one form to another.
  • Examples of energy transformations:
    • Chemical (battery) → Sound (mobile phone)
    • Chemical (food) → Kinetic (movement)
    • Nuclear → Electrical → Sound, Heat, or Kinetic
  • The principle of conservation of energy states that energy is always conserved during transformations.

Sankey Diagrams

  • Sankey diagrams illustrate energy flow to and from a device.
  • Arrow width represents the proportion of energy.
  • Example: Comparing light energy output from different lamps relative to electrical energy input.
    • Filament lamp: 2% light energy
    • LED light: 20% light energy
    • CFL: 8.9% light energy

Wasted Energy and Energy Dissipation

  • Energy dissipation: Transformation from a useful form to a less useful form (e.g., heat).
  • Energy conservation involves reducing wasted energy.
  • Example: Body heat produced while walking dissipates into the air.

Examples of Energy Changes

  • Solar water heater: Solar energy → Heat energy (some energy is dissipated, but design improvements increase efficiency).

Sound Energy

  • Sound travels through vibrating air molecules.
  • Kinetic energy transforms: vocal cords → air in mouth → air in the room → ear drum.
  • Human ear: Detects sounds of extremely small energy; very sensitive to energy.
  • Speed of sound: Approximately 340 ms−1340 \text{ ms}^{-1} in air.

Bicycle Dynamo

  • Dynamo: Converts mechanical energy into electrical energy.
  • Energy transformations in cycling:
    • Chemical (food) → Kinetic (cycling) → Electrical (dynamo) → Light (bulb)
    • Energy is dissipated as heat from the body, resistance from the breeze, and heat from the bulb.

Sound Energy Demonstration

  • Tuning fork and ping-pong ball experiment demonstrates sound energy.