Energy – Whenever we do any work, we feel tired as we expend some energy. Energy spent appears in the form of work done. Energy is defined as the ability of a body to do work. Energy has the same units as that of work.

S.I. unit of energy is “joule’, same as that of work. Since work is a scalar, energy is also a scalar quantity.


Types of Energy

  1. Mechanical energy
  2. Heat energy
  3. Light energy
  4. Sound energy
  5. Electrical energy
  6. Nuclear energy

Mechanical energy is classified further into potential energy and kinetic energy. Energy can neither be created nor be destroyed but it can be transformed from one form to another. This is known as the law of conservation of energy.


Kinetic energy

Object in motion possess energy. We call this energy kinetic energy.

A falling coconut, a speeding car, a rolling stone, a flying aircraft, flowing water, blowing wind, a running athlete etc. Possess kinetic energy. In short, kinetic energy is the energy possessed by an object due to its motion. The kinetic energy of an object increases with its speed.


Potential energy

The energy gets stored due to the work done on the object. The energy transferred to an object is stored as potential energy if it is not used to cause a change in the velocity or speed of the object.

You transfer energy when you stretch a rubber band. The energy transferred to the band is its potential energy. You do work while winding the key of a toy car. The energy transferred to the spring inside is stored as potential energy. The potential energy possessed by the object is the energy present in it by virtue of its position or configuration.


Heat energy

Heat is an invisible form of energy that can produce the sensation of heat or cold. The property that tells us how hot or cold a particular body is called its temperature, i.e., the degree of hotness or coldness of a body is denoted by its temperature . When heat is supplied to a body its temperature increases and when heat is taken away from a body , its temperature decreases. The heat energy can be transformed into other forms of energy like electrical, mechanical, light, etc., by suitable methods . Heat energy can bring about changes in the physical dimensions , state and the chemical properties of a substance.

Heat energy can also be defined as the sum total of potential and kinetic energy of molecules. Temperature can also be defined as the average kinetic energy of all molecules.


Light energy

When rays of light coming from an illuminated object strike the eye, an object is seen . Thus, light is necessary to see an object . During the day time, we see objects due to light from the sun. Sun is the main and a natural source of light . At night we receive light from stars, moon, bulbs, candles, etc.


Sound energy

Sound is a form of energy which produces a sensation of heating in our ears. There are also ather forms of energy like mechanical energy, light energy, etc.


Nuclear energy

Nuclear Energy Many years ago, atom was believed to be the most fundamental and indivisible entity of matter. Later on, it was discovered that atom too is divisible and it consists of elementary particles like protons, neutrons and electrons. Protons, that are considered to be positively charged and neutrons that do not possess any charge are contained in the central part of an atom called nucleus, where the mass of the atom is concentrated. Electrons that are considered to be charged negatively revolve around the nucleus in their specified paths called orbits.

In the formation of atom from its constituents, energy is released and thus, energy transactions are related to the reactions that are linked with the nuclei. These reactions are called nuclear reactions. There are broadly two types of nuclear reactions: nuclear fission and nuclear fusion.

Nuclear fission is a process in which a heavy nucleus of an atom is split into two atoms of lighter nuclei by bombarding it with slow moving particles like neutrons resulting in the release of a huge amount of energy. The energy released in the fission process is in the form of heat and can be conveniently utilized to produce electricity using turbines.

Nuclear fusion is a process in which two lighter nuclei, like hydrogen, are combined at high temperatures to form a single atom having heavier nucleus like helium. In nuclear fusion. an enormous amount of energy which is greater than that produced in a fission reaction is released. The energy from the sun and other stars is based on the nuclear fusion phenomenon whereas energy released in the explosion of atom bombs is based on nuclear fission.

Nuclear fusion is a process in which two lighter nuclei combine to form heavy nucleus with release of energy. For example, four hydrogen atoms combine to form helium nucleus with the release of energy. For fusion to take place a very high temperature of the order of 10 K is required. Energy released per unit mass in fusion is greater than the energy released per unit mass in fission.

Nuclear reactor is a device in which a controlled nuclear fission reaction takes place. The nuclear fuel, either uranium 235 or plutonium, is bombarded with slow moving neutron and this releases energy in the form of heat and radiation. The fission reaction producing neutrons is controlled in the reactor, and hence, the energy is released at a constant rate. The heat energy received during fission reaction is absorbed by the coolant (water) and the water is converted into steam. The steam is used to rotate the turbine placed between two strong magnetic poles. This in turn generates electricity. Nuclear waste obtained from fission reaction is radioactive and it gives out radiations which cause hazards to the living beings. diseases such as cancer, leukaemia, etc. Some of the nuclear power plants in India are at Tarapur. Kota, Kalpakkam, Narora, etc. The working of a nuclear reactor is based on the phenomenon of nuclear fission. In a nuclear reactor, the fission reactions that take place can be controlled and the energy derived from it is harnessed into productive applications. But in the case of fusion reactions, the energy released cannot be harnessed into productive applications as the fusion reactions cannot be controlled. A hydrogen bomb is based on a nuclear fusion reaction. The reason for the controlled fusion reactions that take place in the sun and stars is yet to be established.


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