There are three basic units in electricity which are

  • Voltage (V),

  • Current (I or A)

  • Resistance (r).

Voltage is measured in volts, current is measured in amps and resistance is measured in ohms.

To help understand these terms plumbing pipes can be used as an example. Voltage is equivalent to the water pressure, the current is equivalent to the flow rate, and the resistance is like the pipe size.
 

Watts (W) used extensively in electric flight, determines electrical power, i.e. The equivalent of the horse power developed by an engine.

For example 1 horsepower = 748 watts.

(Note: The metric equivalent of horsepower is the Pferdestarke (PS).   1 horsepower = 1.0139 PS = 750 watts.)

Based on information available the diagram on the right enables calculations to be determined using various formula.

For example Current can be determined by Watts divided by Volts.

300watts / 11.1volts = 27Amps