- Definition of Electrical Energy Unit: The unit of electrical energy is the joule, which is defined as the energy needed to move one-ampere current through one volt in one second.
- Commercial Unit: The commercial unit of electrical energy is the watt-hour, and larger measurements use kilowatt-hours (kWh), which equals 1000 watt-hours.
- Mechanical Energy Relation: Mechanical energy is measured in joules, the same as electrical energy, linking both through their definition and usage.
- Heat Energy Relation: Heat energy is measured in calories, BTUs, and CHUs, with one calorie equivalent to 4.18 joules.
- Electrical Energy Equivalents: Electrical energy equivalents are used to compare and convert electrical energy to common heat energy units like calories and BTUs.
The unit of electric power is the watt, so the unit of electrical energy is the watt-second, the product of power and time. The watt-second is the joule. One joule is the work needed to drive one-ampere current for one second between two points with a potential difference of one volt. So one joule of electrical energy equals one volt times one ampere times one second.
A joule, equal to one watt-second, is a small unit, so bills and plant meters do not use it for everyday consumption.
Commercial Unit of Electrical Energy
Meters and bills therefore use a larger commercial unit of electrical energy called the watt-hour.
A still larger unit is the kilowatt-hour, or kWh, equal to 1000 watt-hours.
Relation between Unit of Electrical Energy and Unit of Mechanical Energy
A unit of mechanical energy is the work needed to move an object one meter with a force of one newton. That quantity is also a joule. One joule of electrical energy equals one watt-second, so the electrical and mechanical joules are the same SI unit.
Relation between Unit of Electrical Energy and Unit of Heat Energy
Heat is another form of energy used in engineering. Heat units include the calorie, British thermal unit (BTU) and centigrade heat unit (CHU). One calorie is the heat needed to raise the temperature of one gram of water by one degree Celsius. The thermochemical calorie is 4.184 joules; textbooks often round that to 4.18 joules.
The calorie is small, so engineering work often uses the kilocalorie. One kilocalorie is the heat required to raise the temperature of 1 kg of water by 1oC.
The British thermal unit is the heat required to raise the temperature of 1 pound of water by 1oF.
The Centigrade heat unit is an older unit: the heat required to raise the temperature of 1 pound of water by 1oC. Modern work uses the joule or BTU instead.
The mechanical work needed to raise the temperature of one gram of water by one degree Celsius is about 4.18 joules. So one calorie is about 4.18 joules. The conversion GIFs below keep that textbook rounding.
Electrical Energy Equivalent of Centigrade Heat Unit
Electrical Energy Equivalent of British Thermal Unit
