Power is the rate at which energy is transferred. The amount of energy usefully transferred in a system determines how efficient that system is.
What are the correct units for energy transferred (work done)?
Energy transferred (work done) is measured in joules, J
Energy transferred (work done) is measured in amps, A
Energy transferred (work done) is measured in newtons, N
What is the correct unit for power?
Which of the following is a definition of power?
The work done by a force
Energy transferred × time taken
Energy transferred ÷ time taken
A hairdryer transfers 10,000 J of energy in 4 s. What is its power?
Which of these cannot happen to energy?
Energy cannot be stored
Energy cannot be dissipated
Energy cannot be created
A 60 W lamp is left on for 20 s. How much energy is transferred in this time?
In an electric kettle, what energy is not wasted?
The energy that heats the water
The energy that dissipates out of the kettle into the surroundings
The sound heard as the kettle boils
How can the thermal store of a house be prevented from dissipating for as long as possible?
Increase the thermal conductivity of the walls
Insulate the walls of the house
Keep the heating on its highest setting
What is the efficiency of Christmas lights that give out 10 J of light radiation for an electrical input of 200 J?
How might a toy car be made more efficient?
Push it with a greater force
Press down on it harder
Add a little oil to the moving parts