Chapter 1: WORK AND ENERGY
WORK
In ordinary language the word "work" means almost any physical or mental activity but in physics it has only one meaning:Work is done when a force produces motion.For example, when an engine moves a train along a railway line,it is said to be doing work;a horse pulling the cart is also doing work;and and man we
The work done by on a body depends on two factors:
1.Magnitude of the force, and
2.Distance through which the body moves
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 posses energy.
The amount of energy possessed by a body is equal to the amount of work it can do when its energy is released.
Energy is a scalar quantity.It has only magnitude but no direction.
There are different forms of energy:
1.Kinetic Energy
2.Potential energy
3.Chemical energy
4.Heat energy
5.Sound energy
6.Sound energy
7.Electrical energy
8.Nuclear energy
POWER
Power is the rate at which work is done or energy is consumed.
Power is a scalar quantity which has only magnitude but no direction.
COMMERCIAL UNIT OF ENERGY
The commercial unit of energy is kilowatt-hour which is written in the short form kWh. Kilowatt-hour is usually used as a commercial unit of electrical energy.
The SI unit of electrical energy is joule and we know that"A joule is the amount of electrical energy consumed when an appliance of 1 watt power is used for one second.
LAW OF CONSERVATION OF ENERGY
1.Energy can neither be created not destroyed.
2.During the conservation of energy from one form to another some energy may be wasted.
TRANSFORMATION OF ENERGY
Energy exists in many different forms.One form of energy can be changed into another form.The change of one form of energy into another form of energy.When a body is released from a height then the potential energy of the body is gradually transformed into kinetic energy.When a body is thrown upwards, the kinetic energy of body is gradually transformed into potential energy.
USING ENERGY CONVERTERS
1.Electric motor
2.Electric iron
3.Electric bulb
4.Radio
5.Steam engine
6.Car engine
7.Cell
8.Gas stove
9.Solar water heater
10.Solar cell
LAW OF CONSERVATION OF ENERGY
Energy can be transformed from one form of another.According to the law of conservation of energy: Whenever energy from one form to another, the total amount of energy remains constant.Another definition of the law of conservation of energy is that: Energy can neither be created nor destroyed.
During the conversion of energy from to another,some energy may be wasted.Although some energy may be wasted during conversion,but the total energy of the system remains the same.
For example, when electrical energy is converted into light energy in an electric bulb,then some electrical energy is wasted in the form of heat.
1 kilowatt-hour is equal to 3.6×10^6 joule of electrical energy.It should be noted that watt or kilowatt is the unit of electrical power but kilowatt-hour is unit of electrical energy.
The electrical energy used in homes,shops and industries is measured in kilowatt-hour (kWh).The electricity meter installed in our home records the electrical energy consumed by us in kilowatt-hours.
1 kilowatt-hour of electrical energy is commonly known as '1 unit' of electricity.One unit of electricity may cost anything from Rs3 to Rs5.
TRANSFORMATION OF ENERGY
Energy exists in many different forms.One form of energy can be changed into another form.The change of one form of energy into another form of energy is known as transformation of energy.We will now take some examples to show how the transformation of energy takes place.Suppose a stone is lying on the roof of a house.In this position,all the energy of the stone is in the form of potential energy.As the stone continues falling downwards towards the ground and the potential energy of stone starts changing into kinetic energy.
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