Energy transfers

Question 1

What are the different types of energy stores?

Answer 1

• Chemical energy – Stored in fuels, food, and batteries due to chemical bonds.
• Kinetic energy – Energy of a moving object, depends on mass and speed.
• Gravitational potential energy (GPE) – Energy stored in an object due to its height above the ground.
• Elastic potential energy – Energy stored in stretched or compressed objects like springs or rubber bands.
• Thermal (internal) energy – The total energy of the particles in an object, linked to temperature.
• Magnetic energy – Energy stored due to magnetic fields acting on objects.
• Electrostatic energy – Energy stored due to the interaction of electric charges.
• Nuclear energy – Stored in the nucleus of atoms, released in nuclear reactions.

Question 2

How can energy be transferred?

Answer 2

• Mechanically – When a force is applied to an object, causing it to move (e.g., pushing a car).
• Electrically – When electric charges move through a circuit (e.g., powering a lamp).
• By heating – When thermal energy moves from a hotter object to a cooler one (e.g., boiling water).
• By radiation – Through electromagnetic waves such as light and sound (e.g., sunlight warming the Earth).

Question 3

State the principle of conservation of energy.

Answer 3

• Energy cannot be created or destroyed.
• It can only be transferred from one form to another.
• The total energy in a closed system remains constant.

Question 4

What is the efficiency equation?

Answer 4

Efficiency = (useful energy output / total energy input) × 100%
- Efficiency is always less than 100% due to wasted energy (e.g., heat loss due to friction).
- The more efficient a device, the less energy is wasted.
- Efficiency can be improved by reducing friction, insulation, or using better conductors.

Question 5

Describe examples of energy transfer in everyday devices.

Answer 5

• Electric heater: Electrical energy → Thermal energy.
• Car engine: Chemical energy (fuel) → Kinetic + Thermal energy.
• TV: Electrical energy → Light + Sound + Thermal energy.
• Sankey diagrams visually represent the efficiency of energy transfers by showing useful and wasted energy flows.

Question 6

How does thermal energy transfer occur?

Answer 6

• Conduction: Transfer of heat through solids via vibrating particles.
• Convection: Heat transfer in fluids (liquids/gases) through the movement of warm, less dense regions.
• Radiation: Transfer of heat as infrared waves, which can travel through a vacuum.
• Different materials transfer heat at different rates depending on their conductivity.

Question 7

Explain conduction in detail.

Answer 7

• Conduction occurs mainly in solids due to particle vibrations.
• When a solid is heated, its particles gain kinetic energy and vibrate more.
• These vibrations pass energy to neighboring particles, transferring heat.
• Metals are good conductors because they have free electrons, which move and transfer energy quickly.
• Insulators (e.g., wood, plastic) are poor conductors as they lack free-moving electrons.
• The rate of conduction depends on the thermal conductivity of the material.

Question 8

Explain convection in detail.

Answer 8

• Convection occurs in fluids (liquids and gases) where heated regions become less dense and rise.
• Cooler, denser fluid moves in to replace it, creating a convection current.
• Examples:
  
  • Boiling water: Water at the bottom heats up, rises, and cooler water moves in to replace it.
  • Radiators: Warm air near the radiator rises, and cooler air moves in to replace it.
  • Sea breezes: Land heats up faster than the sea, causing warm air to rise over land and cooler air from the sea to move in.
• The larger the temperature difference, the stronger the convection current.

Question 9

Explain radiation in detail.

Answer 9

• Radiation is the transfer of heat in the form of infrared waves.
• Unlike conduction and convection, radiation does not require a medium and can travel through a vacuum.
• The rate of radiation depends on:
  
  • Surface color and texture:
    
    • Dark, matte surfaces absorb and emit radiation efficiently.
    • Light, shiny surfaces reflect radiation, reducing heat transfer.
  • Temperature:
    
    • Hotter objects emit more infrared radiation than cooler ones.
• Examples:
  
  • The Sun heating the Earth through space.
  • Thermal imaging cameras detecting heat emitted by objects.
  • Vacuum flasks using reflective surfaces to reduce heat loss by radiation.

Question 10

How can thermal energy transfer be investigated?

Answer 10

Equipment:
- Metal rods of different materials.
- Heat source (Bunsen burner, hot plate).
- Wax, thermometer, Leslie cube (for radiation experiments).

Method:
- Conduction: Attach wax to the end of different metal rods, heat one end, and measure the time taken for the wax to melt.
- Convection: Heat water in a beaker, place potassium permanganate crystals, observe convection currents forming as the water moves.
- Radiation: Use a Leslie cube with different surfaces (matte black, shiny, white) and measure infrared radiation emitted with a thermal detector.

Results:
- Metals with higher conductivity transfer heat faster.
- Convection currents form as warm fluid rises and cooler fluid replaces it.
- Matte black surfaces emit the most radiation, shiny surfaces the least.

Question 11

How can energy loss be reduced?

Answer 11

• Insulation: Reduces conduction (e.g., foam, wool, double glazing).
• Trapped air layers: Prevent convection (e.g., cavity wall insulation, vacuum flasks).
• Shiny surfaces: Reduce heat loss by radiation (e.g., thermal blankets, reflective surfaces).
• Lubrication: Reduces friction and unwanted thermal energy loss in machines.
• Draft excluders: Reduce heat loss in buildings by stopping air movement.