A student does 100 J of work on the handle of a bicycle pump. The pump does 40 J of work pushing the air into the tire. What is the efficiency of the pump?
I calculate 40% efficiency.
The efficiency of a device can be calculated using these steps:
1) Measure the amount of work put in (input);
2) Measure the work that the device puts out (output);
3) Divide the output by the input;
4) Multiply by 100 to get a percentage.
As an equation, this becomes:
The input is the
Efficiency values are always expressed as percentages. This pump is not particularly efficient - less than half the work put in by the student is actually used to pump air! The rest is converted to heat and sound, then lost to the surroundings.