The energy consumed by a (or furnished to) device is equal to the product or the power by the time interval the device is on. The next formulas are use to calculate the Electric Energy sourced or consumed.
Formula 1
W = P x I
Where:
W is the amount of consumed (or furnished) in watts/second (Ws) or joules (J)
P is the device Power in watts (W) or joules/second (J/S)
t is the time the device is on in seconds (s)
Derivated Formulas:
Formula 2
P= W/T
Formula 3
t=W/P
Application Example:
How much energy is consomed by a 100 W lamp in 10 minutes?
Data:
P = 100 W
t = 20 minutes = 1 200 seconds
W = ?
Using Formula 1:
W = 100 x 1 200 = 120 000 joules
Note: The consumed (or furnished) energy can also be calculated in kilowatts-hour (kWh). For the application example the calculation is made as follows:
Data:
100 W = 0,1 kW
t = 20 minutes = 1/3 hour = 0,333 hours
W= ?
W = 0,1 x 0,333 = 0,0333 kWh
