Energy

• What is a system in the context of energy changes?

  A system is an object or group of objects.
• What happens to energy when a system changes?

  Energy is transferred between different energy stores.
• Name one type of energy store.

  Thermal
• What are the different types of energy stores?

  • Thermal
  • Chemical
  • Kinetic
  • Magnetic
  • Gravitational potential
  • Electrostatic
  • Elastic potential
  • Nuclear
• How is energy transferred mechanically?

  By a force doing work.
• What is one way energy is transferred electrically?

  By moving charges doing work.
• What is a closed system?

  A closed system is one where neither matter nor energy can enter or leave.
• What is the net change in total energy of a closed system?

  The net change is always zero.
• In the example of boiling water, what is the system?

  The water is the system.
• How does energy transfer occur when boiling water?

  Energy is transferred to the water by heating from the heating element.
• What is work done in the context of energy transfer?

  Work done is another way of saying energy transferred.
• When is work done in a circuit?

  When current flows and does work against resistance.
• What are the changes in energy storage when a system changes?

  1. An object projected upwards: Chemical to kinetic energy.
  2. A moving object hitting an obstacle: Kinetic to elastic potential and sound energy.
  3. An object accelerated by a constant force: Gravitational potential to kinetic energy.
  4. A vehicle slowing down: Kinetic to thermal energy.
• What is the formula for kinetic energy?

  E_k = \frac{1}{2}mv^2
• What does lifting an object in a gravitational field require?

  It requires work, causing energy transfer to the gravitational potential energy store.
• What is the formula for gravitational potential energy?

  E_p = mgh
• What is specific heat capacity?

  It is the amount of energy needed to raise the temperature of 1g of a substance by 1℃.
• How can the change in thermal energy be calculated?

  ΔE = mcΔθ
• What is the procedure to investigate a solid material's specific heat capacity?

  1. Measure the mass of the block.
  2. Wrap it in an insulating layer.
  3. Insert thermometer and heater.
  4. Measure initial temperature.
  5. Turn on power supply and start stopwatch.
  6. Record temperature and current every minute.
  7. Calculate power and energy transferred.
  8. Plot energy transferred against temperature.
  9. Find gradient to determine specific heat capacity.

  10. Repeat with different materials.
• What is power in the context of energy transfer?

  Power is the rate of energy transfer or the rate of doing work.
• What is the formula for power?

  Power = \frac{\text{Energy transferred}}{\text{time (s)}}
• How is one watt defined?

  One watt is equal to 1 joule of energy transferred per second.
• What does it mean for a machine to be powerful?

  A powerful machine transfers a lot of energy in a short time.
• What happens to energy when it is transferred between objects?

  Not all energy is transferred usefully; some is dissipated as waste energy.
• What is conduction?

  Conduction is the process where vibrating particles transfer energy to neighboring particles.
• What is thermal conductivity?

  Thermal conductivity measures how quickly energy is transferred through a material using conduction.
• What is convection?

  Convection is where energetic particles move away from hotter to cooler regions.
• How can friction be reduced between moving objects?

  By using lubricants, which are usually liquids.
• What are methods to reduce energy transfer by heating?

  • Cavity wall insulation reduces conduction.
  • Double glazed windows prevent conduction.
  • Draught excluders reduce convection.
  • Thicker walls with low thermal conductivity slow energy transfer.
• What is the procedure to investigate the effectiveness of materials as thermal insulators?

  1. Boil water and pour into a container.
  2. Measure initial temperature.
  3. Seal and leave for five minutes.
  4. Measure final temperature.
  5. Repeat with different insulating materials.
  6. Lower temperature difference indicates better insulation.
• What does higher efficiency in a device mean?

  The less energy wasted, the more efficient the device is.
• What is the first step in the experiment involving water in a flame?

  Pour some of the water into a sealable container to a safe level.
• What should be done after pouring water into the container?

  Secure the mass of water in the container.
• How is the initial temperature of the water measured?

  Using a thermometer.
• What should be done after sealing the container?

  Leave it for five minutes.
• What tool is used to measure the time during the experiment?

  A stopwatch.
• What is the next step after measuring the time?

  Remove the lid and measure the final temperature of the water.
• What should be done with the water after measuring the final temperature?

  Pour away the water and allow the container to cool to room temperature.
• What should be done in the repeated experiment regarding the container?

  Wrap the container in a different material once secured.
• Why is it important to use the same mass of water at the same initial temperature each time?

  To ensure consistent results in the experiment.