L4 Efficiency

L4 Efficiency

Multiple Choice

If we took a light bulb, what type of energy would be useful?

• kinetic energy

• gravitational potential energy

• light energy

• thermal energy

Multiple Choice

From our light bulb, what would be the wasted energy?

• chemical energy

• thermal energy

• light energy

• kinetic energy

Poll

What about a speaker connected to your computer? The useful energy would be

• light energy

• electrical energy

• sound energy

Multiple Select

In our speaker, the wasted energy would be

• electrical energy

• sound energy

• thermal energy

Open Ended

If my son left the TV on (again!) and 500J of energy were input (from the power supply). How much energy would be wasted if 300J of useful light energy was output (given out)?

500J total input = 300J useful output (light) + ? J wasted output (thermal)

Open Ended

If my dog left the light on (again!) and 200J of energy were input (from the power supply). How much energy would be wasted if 125J of useful light energy was output (given out)?

200J total input = 125J useful output (light) + ? J wasted output (thermal)

Open Ended

Write the equation that links efficiency, useful energy transfer and total energy transfer

Multiple Choice

If a kettle transfers 170,000J of energy when it is switched on to boil some water and 162,000J is used to actually heat the water, the efficiency of the kettle can be calculated as:

• 
  

  $\frac{162,000J}{170,000J}\ \ =\ 0.63$

• $\frac{170,000J}{8,000J}\ \ =\ \ 21.25$

Open Ended

Calculate the % efficiency of a light that uses 2000J to light up of which 500J of energy is used as useful light energy.

(To convert your efficiency calculation to a %, you need to multiply your answer by 100) :)

You Do - Calculating Efficiency

• Answer the next 4 questions into your book - you don't need to write our the questions

• Then self assess your answers with a green pen