Energy
ENERGY-SOURCES-FORMS OF ENERGY
¶¶ Introduction to Energy
It is often said that a person A is more energetic than a person B. The meaning of this statement is that a person A can do more work than the person B. Similarly, a person after doing a lot of work gets tired and after that he is not able to do much work. It is clear that a person doing work expends something. This ‘something’ is known as the energy of the person. The energy spent by a person is equal to the work done by him. Human beings and animals get energy by eating food.
It may be noted that anything which is capable of doing work has energy. For example, the steam pushes up the lid placed on the boiling water container. It means, the steam has the ability or capacity to do work. The work done by the steam on the lid is equal to the energy of the steam.
ENERGY
If a person can do a lot of work we say that he has a lot of energy or he is very energetic. In physics also, anything which is able to do work is said to possess energy.
Thus, energy is the ability to do work or the capacity to do work.
¶¶ Units of energy
Unit of energy is same as that of the unit of work as work is a form of energy.
So, S.I. unit of energy is Joule (J).
When we say that energy of a body is 1 joule, it means, this body has the capacity to do 1 J work.
¶¶ Commercial unit of Energy
The commercial unit (or trade unit) of energy is kilowatt-hour which is written in short form as kWh. Kilowatt-hour is usually used as a commercial unit of electrical energy.
One kilowatt-hour is the amount of electrical energy consumed when an electrical appliance having a power rating of 1 kilowatt is used for 1 hour. Since a kilowatt means 1000 watts, so we can also say that one kilowatt-hour is the amount of electrical energy consumed when an electrical appliance of 1000 watts is used for 1 hour.
1 kilowatt-hour is the amount of energy consumed at the rate of 1 kilowatt for 1 hour. That is, 1 kilowatt-hour = 1 kilowatt for 1 hour
or 1 kilowatt-hour =1000 watts for 1 hour
Note: Watt or kilowatt is the unit of electrical power but kilowatt-hour is the unit of electrical energy. Energy is a scalar quantity.
Dimensional formula of energy = ML2T-2