D - Energy Transfer Flashcards
A lift motor uses 6000 J of energy every second. Of this only 3100 J is converted into gravitational potential energy. Draw a Sankey diagram to represent this.
Construct an energy transfer diagram to show the energy transfer that takes place in a loudspeaker.
Construct an energy transfer diagram to show the energy transfer that takes place in a kettle.
Construct an energy transfer diagram to show the energy transfer that takes place in a gas fire.
State the equation for efficiency
efficiency = useful energy output / total energy input
A fluorescent bulb uses 11 joules per second of energy. It is reckoned that it only uses 2.5 joules for light.
efficiency = useful energy output / total energy input
efficiency = 2.5 / 11 x 100
= 0.227 x 100
= 22.7% efficient
A gas boiler uses 4000 joules of energy. Around 3700 joules of this ends up as heat energy in the water that is being heated.
efficiency = useful energy output / total energy input
efficiency = 3700 / 4000 x 100
= 0.925 x 100
= 92.5% efficient
What is the purpose of a Sankey Diagram?
To show the input and ouput energy in a system and show the efficiency of energy transfer.
Why is electricity described as a secondary energy source?
It is generated from another energy source such as fossil fuels or nuclear power.
What are the three ways heat can be transfered?
- Conduction
- Convection
- Radiation
A device produces 268J of useful energy for an input of 654J of energy.
Calculate the efficiency of the device.
Give the answer as percentage to the nearest whole number.
41%
A 1200W hairdryer is used for 15 minutes. How many joules of energy are transferred?
Power = work done/ time taken
Work done = Power x time taken
1200 x 15 x 60 = 1080000J
Calculate the height of a ball if it has 30J of gravitational potential energy. (Use g = 10m/s2 )
PE = mgh
30=0.16x 10 x h
h = 30/0.16 x 10
18.75m
What is meant by the phrase conservation of energy?
Energy cannot be created or destroyed.
