Electrical Energy Calculations
Electrical energy is the amount of power that we use over a period of time. We use it a lot in things like power systems and electrical engineering. We also use it to figure out how energy we are using.
1. The Formula For Electrical Energy
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To calculate energy we use a simple formula:
E = P times t
Where
E is the electrical energy in Joules or kilowatt hours
P is the power in watts
and t is the time in seconds or hours
2. Calculating Energy Using Voltage and Current
We can also calculate power using voltage and current:
P = V times I
So electrical energy is
E = V times I times t
Where
V's the voltage in volts
I is the current in amperes
and t is the time
3. Units of Electrical Energy
We use units to measure electrical energy:
Unit Symbol Description
Joule J this is the basic unit of energy
Watt-hour Wh this is the power used for one hour
Kilowatt-hour kWh this is one thousand watt hours and it is used on our electricity bills
For example
one kilowatt hour is equal to one thousand watts times one hour
4. Some Examples
Lets say we have a lamp that uses one hundred watts and it runs for ten hours.
To calculate the energy we use the formula:
E = one hundred times ten
E = one thousand watt hours
E = one kilowatt hour
So the lamp uses one kilowatt hour of electrical energy.
Another example is a motor that runs at
Voltage = two hundred twenty volts
Current = five amperes
Time = three hours
First we calculate the power:
P = V times I
P = two hundred twenty times five = one thousand one hundred watts
Then we calculate the energy:
E = P times t
E = one thousand one hundred times three = three thousand three hundred watt hours
E = three point three kilowatt hours
5. Calculating The Cost of Electrical Energy
To calculate the cost of electricity we use the formula:
Cost = Energy in kilowatt hours times Price per kilowatt hour
For example
if one kilowatt hour costs fifteen cents and we use fifty kilowatt hours
Cost = fifty times zero point one five
Cost = seven point five
So the total cost is seven dollars and fifty cents.
6. Formulas For Different Types of Circuits
For a current circuit
E = V times I times t
For a resistive circuit we can use Ohms Law:
E = I squared times R times t
or
E = V squared over R times t
Where R is the resistance in ohms.
The Main Points
We have a few formulas that we can use:
E = P times t to calculate basic energy
E = V times I times t to use voltage and current
E = I squared times R times t to use current and resistance
E = V squared over R times t to use voltage and resistance
An infographic that explains the electrical energy formulas, in a visual way.
