Q3 EC #1 Due Monday 2/11/13
Energy Transfer
1. Explain/define the following energy listed and indicate an example of
each
Energy
Thermal
Explanation & Example
Light
Sound
Elastic
Gravitational
Kinetic
Electrical
Chemical
Nuclear
Energy can be changed from one form to another.
Examples:
1. Chemical energy in food is converted to thermal energy and kinetic energy by
our bodies.
2. Gravitational energy in a ball is converted to kinetic energy when it falls to the
ground.
2. What are the energy transfers for the following objects?

A match burning is chemical energy to thermal energy

A portable torch

A microphone
Q3 EC #1 Due Monday 2/11/13

A radio

A TV

A catapult

A car
Remember that in all transfers energy is conserved. Energy cannot be created or
destroyed. Energy is measured in Joules (J).
Energy transfer diagram like the one below are also known as Sankey diagrams.
Efficiency
(efficiency = useful energy output/ total energy input)
What is the efficiency of the following appliances?
1. A 3 kW kettle that transfers 3000 J of electrical energy into 2900 J of heat
energy in the water, and 100 J of wasted heat and sound energy.
2. A 2 kW heater that transfers 2000 J of electrical energy into 1980 J of heat
energy, and 20 J of sound energy.
3. A 400 W computer that transfers 400 J of electrical energy into 350 J of
kinetic, light, and sound energy, and 50 J of wasted heat and sound energy.
What is the useful output energy of the following?
4. A 95% efficient fridge supplied with 800 J of electrical energy.
5. A 98% efficient microwave, supplied with 750 J of electrical energy.
6. A 35% efficient car engine, supplied with 5000 J of chemical potential
energy.
How much energy must be supplied to give a useful output of 1 kW when the
efficiency is...
7. 50 %
8. 75%
9. 84%
Q3 EC #1 Due Monday 2/11/13