Calculating energy: E = Pt

• How would you calculate energy if power is 50W and time is 4s?

  $E =$$200 \text{ joules (J)}$
• What does the formula $E =$$Pt$ represent?


  Energy transferred equals power times time
• What does the variable $E$ represent in the formula?


  Energy in joules (J)
• Why is a transformer used in the power plant system?

  To step up the voltage for efficient transmission of the electrical energy over long distances
• What is the purpose of the turbine in the power plant system?

  To convert the kinetic energy of the steam into mechanical energy to spin the generator
• What does $E$ represent in the formula $E =$$Pt$?


  Energy transferred in joules (J)
• What unit is used for power in electrical appliances?

  Watts (W)
• How could the efficiency of the energy transfers in an electric motor be improved?

  • Reduce losses to thermal energy (e.g. improve insulation, reduce friction)
  • Optimize the conversion of electrical energy to kinetic energy
  • Minimize the generation of unwanted sound energy
• If an appliance has a power rating of 200 W and is used for 300 seconds, what is the energy used?

  $60,000 J$
• How does a hairdryer demonstrate energy transfer?

  It converts electrical energy into thermal energy
• How does the efficiency of the power plant system compare to the energy input from the fuel?

  • Energy in fuel: 100 J
  • Electrical energy output: 35 J
  • Efficiency = Electrical energy output / Energy in fuel = 35%
• What are the main components of a power plant system shown in the image?

  • Boiler
  • Turbine
  • Generator
  • Transformer
• How does the energy transfer process shown in the image compare to the energy transfers in other types of electrical devices?

  The energy transfer process may differ depending on the specific device, as the inputs, intermediate steps, and outputs can vary
• What does the variable $P$ represent in the formula?


  Power in watts (W)
• What are the different types of energy shown in the image?

  Electrical energy, kinetic energy, sound energy, and thermal energy
• How much energy does a 60W light bulb transfer when it runs for 30 minutes?

  108,000 joules
• How much energy is transferred if the power output is 500 million watts for 1 minute?

  30 billion joules
• How does the energy used by a light bulb compare to that of a fan?

  Light bulb uses 360,000 J, fan 30,000 J
• What does the variable $t$ represent in the formula?


  Time in seconds (s)
• How do you calculate electrical energy used by appliances?

  Multiply power rating by time used
• What is the formula for calculating energy?

  $E =$$Pt$
• What is the total energy used by the electric motor?

  9,000 J
• If a light bulb has 100W power and runs for 2 seconds, how much energy is transferred?

  $200 \text{ joules (J)}$
• How do you calculate energy transfer using the formula?

  • Identify power output (P) in watts
  • Convert time (t) to seconds
  • Use the formula: $E =$$Pt$
• What is the definition of energy transfer?

  Energy moves from one form or place to another
• How does the kinetic energy of the steam molecules relate to the movement of the turbine blades?

  As the high-speed steam molecules hit the turbine blades, they transfer their kinetic energy, causing the turbine to spin
• How does the power plant system convert the energy in the fuel into electrical energy?

  • Fuel (coal, gas, nuclear) provides chemical energy
  • Boiler converts chemical energy into heat energy
  • Heat energy turns water into steam
  • Steam turns the turbine, which spins the generator
  • Generator converts the kinetic energy into electrical energy
  • Transformer steps up the voltage for transmission
• What unit is used for energy in electrical appliances?

  Joules (J)
• How is energy defined in the context of the formula?

  Energy is the total amount used in joules
• What are the energy calculations for the listed appliances?

  • Light bulb:
  • Power: 100 W
  • Time: 3600 s
  • Energy: 360,000 J
  • Fan:
  • Power: 50 W
  • Time: 600 s
  • Energy: 30,000 J
  • Electric motor:
  • Power: 10 W
  • Time: 900 s
  • Energy: 9,000 J
• How is time defined in the context of the formula?

  Time determines how long the appliance runs
• How does the image show the relationship between the different energy types?

  • Electrical energy is shown as the input
  • Kinetic energy is shown as an intermediate step
  • Sound energy and thermal energy are shown as the outputs
• What is the energy transferred by a 60W appliance running for 1800 seconds?

  $E =$$60 \times 1800 =$$108,000$ joules
• How many seconds are in 1 minute?

  60 seconds
• What does $t$ represent in the formula $E =$$Pt$?


  Time the appliance runs in seconds (s)
• What is the title of the image?

  Energy Transfers in Electric Motors
• What is the time unit used in the energy calculation?

  Seconds (s)
• How is power defined in the context of the formula?

  Power is how quickly energy is used
• What happens to energy transferred if power increases while time remains constant?

  Energy transferred increases
• Why is it important to convert time to seconds in energy calculations?

  To ensure consistency in units used