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### Efficiency of a motor

The following video demonstrates a simple experiment to determine the efficiency of a small dc electric motor. The video allows various quanitities to be measured: The energy supplied to the motor can be found by measuring the potential difference, current and time taken; The energy given to the lifted masses may be determined from the masss, gravitational field strength and the lift height. These quantities are given in the video.

Because of the number of measured quantities involved in the experiement, if you intend to take measurements from the video it is a good idea to draw up a good results table before hand, such as the one given below:

 Mass (kg) Gravity (N/kg) Height (m) Useful Energy out (J) Potential difference (V) Current (A) Time (s) Total Energy In (J) Efficiency

Note: the various sequences in the video have been shortened.

It should be noted that the efficiencies obtained from this experiment are very low: typically about 2%. This is far lower than the efficiency of a typical electric motor, which can often exceed 90%. The reason for the disparity is because the motor is being run well below its optimum speed. It is also connected to a series of gears, which decrease the efficiency further. The above experiment is intended to demonstrate the concept of efficiency rather than to give a realistic measurement of it in a realistic situation.