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The Joules is the unit of measurement of work. The rate at which the work is done is measured in Joules per second, or Watts, and is called power:
`P = (DeltaW)/(Deltat)` .
For an electric device, the power can be calculated by using a current going through this device (I) and applied voltage (U), and/or resistance of the device (R).
`P = IU = I^2R = U^2/R` (The last two relationships are obtained by using Ohm's Law, which relates current and voltage: U = I*R.)
In this question, we are given that the heater is meant to use is the voltage of 220 Volts, and the power it will use is 1200 Watts.
Since a Watt is a Joule per second, then if the heater is indicated to use 1200 Watts, this means it uses 1200 Joules of electricity per second.
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