Efficiency

• What is the main topic discussed in the material?

  Efficiency in energy transfers
• Why are only useful devices mentioned in energy transfers?

  Because they can transfer energy effectively
• What happens to some of the input energy in devices?

  It is usually wasted during transfers
• How does the efficiency of a device relate to wasted energy?

  The less energy wasted, the more efficient it is
• How can you improve the efficiency of energy transfers?

  By insulating objects and lubricating them
• What equation is used to calculate efficiency in energy transfers?

  Efficiency = Useful output energy / Total input energy
• What can you calculate if you know the power input and output of a device?

  You can calculate its efficiency
• If an appliance has a total input power of $600 \text{ W}$ and is 70% efficient, what is the useful output power?


  $420 \text{ W}$
• How do you convert efficiency from a percentage to a decimal?

  Divide the percentage by 100
• How do you rearrange the equation for useful power output?

  Useful power output = Efficiency × Total power input
• If a device is 70% efficient with a total power input of $600 \text{ W}$, what is the useful power output?


  $420 \text{ W}$
• What is the efficiency of a device that wastes no energy?

  100% efficiency
• What is usually true about wasted energy in devices?

  It is often transferred to useless energy stores
• What is the efficiency of a perfect device?

  100% efficient
• What is the relationship between input and output energy in a device?

  Input energy is greater than output energy
• How does wasted energy affect the overall efficiency of a device?

  More wasted energy means lower efficiency
• If a device has an efficiency of 70%, what decimal form is used in calculations?

  0.7
• What is the significance of knowing the types of energy in input and output?

  It helps in understanding energy efficiency
• What is usually true about the wasted energy in devices?

  It is often transferred to useless energy stores
• What is the efficiency of a device that wastes energy?

  Less than 100% efficiency
• How does the efficiency of a device relate to its design?

  A well-designed device has higher efficiency
• What are the key factors affecting energy transfer efficiency?

  • Usefulness of devices
  • Amount of wasted energy
  • Insulation and lubrication
  • Types of energy involved
• How do you calculate the useful output power of a device?

  1. Determine total input power
  2. Find efficiency as a decimal
  3. Use the formula:

  • Useful output power = Efficiency × Total input power
• What is the relationship between efficiency and wasted energy?

  • Less wasted energy leads to higher efficiency
  • More wasted energy results in lower efficiency
  • Efficiency is a measure of energy conservation
• What is the significance of energy efficiency in devices?

  • Reduces energy waste
  • Lowers operational costs
  • Enhances performance and sustainability
• What is usually not equal to total energy input?

  Useful energy output
• What can you discuss regarding energy types in input and output?

  They can vary in efficiency and usage
• What is the efficiency of any device?

  No device is 100% efficient
• How is wasted energy usually transferred?

  To less useful thermal energy stores
• What are electric heaters considered in terms of efficiency?

  They are the exception to efficiency rules
• Why are electric heaters usually 100% efficient?

  All energy is transferred to thermal energy stores
• What ultimately happens to all energy ends up being transferred to?

  Thermal energy stores
• If you use an electric drill, what happens to its energy?

  It transfers energy to various energy stores
• What should you avoid to save energy while revising?

  Leaving the TV on
• What should you ensure regarding equations for efficiency?

  They can be used and rearranged correctly
• How much energy does a motor transfer into the car's energy stores?

  300 J
• How much energy is transferred to the car's kinetic energy stores?

  225 J
• How do you calculate the efficiency of the motor?

  Use energy output over energy input
• What is the useful power output of a machine?

  900 W
• What is the total power input of the machine?

  1200 W