Energy

Energy: 



Energy is defined as the capacity to do work. Energy is a scalar quantity. The SI unit of energy is joule (J) and erg in CGS system. The amount of energy produced by a body is equal to the amount of work it can do when the energy is released. In nature there exists different forms of energy like mechanical energy, heat energy, light energy, geothermal energy, nuclear energy, tidal energy, wind energy, chemical energy, electrical energy etc.
One joule of energy is the amount of energy which can move an object of weight 1N through 1 meter.
The sun radiates about 27 × 10²³ Kw (or 4×10^26 J/s) of energy per second and earth receives 1.4 Kw of energy per square meter from the sun. Sun is the major source of energy for us  because other form of energy are transformed from the solar energy either directly or indirectly. Energy is produced in the form of heat and light in sun by thermonuclear fusion reaction of hydrogen atoms. Solar energy is the renewable source of energy and it can be used for longer duration.

Law of conservation of energy: 
Law of conservation of energy states that "Energy can neither be created nor be destroyed by it can only be transformed from one form to another.

Sources of energy: 

i. Primary sources: The sources of energy from which we can obtain energy in natural form are called primary sources. Example: wind energy, solar energy, hydro energy, etc.

ii. Secondary sources: The sources of energy which are obtained after modification from the natural form is called secondary sources of energy. Examples: mineral oil, tidal energy etc.

Types of energy: 

i. Renewal source of energy: The sources of energy which can never be used fully are called can be renewed by the natural process are called renewal source of energy. They do not exhaust even after the regular use in a long period of time. E.g: Electricity, wind, geothermal energy, solar energy etc.

a. Solar energy: The energy that is obtained from sun is called solar energy. Solar energy is the best source of energy for all living beings on earth.

ii. Non-renewable source of energy: The sources of energy which can exhaust if once used up fully are called non-renewal source of energy. It takes long period of time to form again. Eg. petroleum oil, coal, natural gas etc.

Difference between renewable and non-renewable source of energy: 

Renewable source of energy	Non-renewable source of energy
1. The source of energy which can never be used up fully and renewed by natural process.	1. The source of energy which exhaust once it is used up fully.
2. They do not get exhausted even if used regularly.	2. They may exhausted due the regular use.
3. Wind energy, solar energy, tidal energy are renewable sources.	3. Petrol, coal and natural gas are the non-renewable source of energy.

Forms of energy and their uses: 
i. Mechanical energy: Mechanical energy is defined as the energy possessed by a moving body or the body resting at a certain place. There are two types of mechanical energy. They are:
   a. Kinetic energy: The energy possessed of a body by virtue of its motion is called kinetic energy. It is written as KE in short. Examples: energy of flowing water, energy of blowing air, energy of a rolling stone, energy of moving vehicles, etc. Let us consider a body with mass 'm' initially at rest is moving with an acceleration 'a', the final velocity of the body moving after certain distance 's' be 'v'. According to the equation of motion:

${{v}^{2}}-{{u}^{2}}=2as$
${{v}^{2}}=0+2as$  [since u=0]
$s=\frac{{{v}^{2}}}{2a}$

Again, KE = work done
                 = $F\times s$
                 = $ma\times \frac{{{v}^{2}}}{2a}$  [Since F = ma and $s=\frac{{{v}^{2}}}{2a}$]
Therefore, KE = $\frac{1}{2}m{{v}^{2}}$
From above equation it is found that KE of an object is directly proportional to the mass and the square of the velocity.

   b. Potential energy: The energy of a body by virtue of its position or configuration is called potential energy. Example: stretched rubber, water stored in a dam, compressed spring etc. In other words when work is done on a body, potential energy is gained i.e the potential energy gained is equal to work done on the body.
If  a body of mass 'm' when it is raised above the ground at certain height 'h' against the gravity, it tendency to fall back to the ground.  The potential energy of the body is equal to the work done in taking the object to height 'h'. Then,
Work done = F × h
                  = mg × h  [f = ma]
Potential energy (PE) = work done in moving the object to the height h.
                                   = mgh.

ii. Nuclear energy: The large amount of energy obtained after fusion or fission of nucleus of an atom or atoms is called nuclear energy.
       a. Nuclear fusion reaction: The reaction in which lighter nuclei fuse together to form a heavy nucleus with release of large amount of energy. The reaction that occur in sun is thermonuclear fusion reaction. Thermonuclear fusion reaction is a process in which two or more nuclei of smaller atoms fuse together to form a heavier atom under high pressure and temperature with the release of huge amount of energy. The reaction that occurs in sun is shown below:

${}_{1}{{H}^{1}}+{}_{1}{{H}^{1}}\xrightarrow{\text{High pressure and themprature}}{}_{1}{{H}^{2}}+{}_{1}{{e}^{0}}+\gamma (energy)$

${}_{1}{{H}^{2}}+{}_{1}{{H}^{1}}\xrightarrow{\text{High pressure and themprature}}{}_{2}H{{e}^{3}}+\gamma (energy)$

${}_{1}{{H}^{2}}+{}_{1}{{H}^{2}}\xrightarrow{\text{High pressure and themprature}}{}_{2}H{{e}^{4}}+\gamma (energy)$

${}_{1}{{H}^{2}}+{}_{1}{{H}^{3}}\xrightarrow{\text{High pressure and themprature}}{}_{2}H{{e}^{4}}+{}_{0}{{n}^{1}}+\gamma (energy)$
${}_{2}H{{e}^{3}}+{}_{2}H{{e}^{3}}\xrightarrow{\text{High pressure and themprature}}{}_{2}H{{e}^{4}}+{}_{1}{{H}^{1}}+{}_{1}{{H}^{1}}+\gamma (energy)$
In short,
$_{1}{{H}^{2}}{{+}_{1}}{{H}^{3}}{{\xrightarrow{\text{High pressure and themprature}}}_{2}}H{{e}^{4}}{{+}_{0}}{{n}^{1}}+\gamma (energy)$
Where,
\[_{1}{{H}^{1}}=\text{Protium,}{{\text{ }}_{1}}{{H}^{2}}=\text{Deuterium, }{}_{1}{{H}^{3}}=\text{Tritium,}{{\text{ }}_{1}}{{e}^{0}}=\text{Positorn,}{{\text{ }}_{0}}{{n}^{1}}\text{= neutron }\]
      b. Nuclear fission reaction: Nuclear fission reaction is the type of reaction in which heavier nucleon disintegrates into lighter fragments with the release of large amount of reaction. With the help of this reaction atomic bomb are made. The nuclear fission reaction of uranium atom is shown below:
$_{92}{{U}^{235}}{{+}_{0}}{{n}^{1}}{{\xrightarrow{{}}}_{56}}B{{a}^{141}}+{}_{36}K{{r}^{92}}+{{3}_{0}}{{n}^{1}}+\gamma (energy)$

iii. Geothermal energy:The heat energy present inside the earth's interior is called geothermal energy. The temperature inside the earth is about 5000°C to 6000°C. When the underground water comes in contact with this huge temperature it changes into steam or hot water. The steam and the hot water is pumped to the earth surface and used to rotate turbine to produce electricity. It is also used to keep house warm.

iv. Hydro-power: The energy that is obtained from the potential and kinetic energy of water is called hydro-power. Hydroelectric energy is the energy generated with the help of water. The water collected in dam or reservoir is made to fall from a certain height through a tunnel or pipe so that the force of falling water turns the turbine which drives the electric generator. With the help of coil and magnetic field electricity is produced. It is the best eco-friendly source of energy. There is wide used of electrical energy because it can be transformed into different other form of energy and apply for different purposes.
Nepal has high potentiality of hydro-power because most of the rivers in Nepal flow from high altitudes with high speed. Nepal has the potentiality of generating About 83000 MW of hydroelectric power. Only few thousands Mega watts of electricity has been produced until now. This clean energy source is boon to our country which boost up the economy if we able to harvest all of the hydroelectric energy.

v. Fossil fuel: Fossil fuel are the energy rich organic materials like oil, coal, natural gas, petroleum etc. which are formed from the dead remaining of plants and animals buried under earth's crust millions years ago. After decomposition the dead remaining turns into fossil fuel which are being used by human nowadays. 

vi. Coal : Coal is defined as an organic sedimentary rock that forms from the accumulation and preservation of dead remaining of plants and animals under the earth crust in a marsh environment. It contains more than 50% of  carbon along with other constituents like hydrogen, oxygen, sulpher etc. 

There are four types of coal on the basis of amount of carbon present in it. They are peat( containing about 50 to 60 percent of carbon), Lignite or Brown coal ( containing 60 - 70 percent of carbon), Sub-Bituminous (containing 70 - 77 percent of carbon), Bituminous ( containing 77 - 89 percent of carbon) and Anthracite or hard coal ( containing 90 - 95 percent of carbon). 
Alternative source of energy:
The cheap and durable source of energy that can be used instead of non-renewable source of energy is called alternative source of energy. Eg: Solar energy, wind energy, tidal energy, biomass etc.

Sun as the ultimate source of energy:

Sun is the main source  of heat and light energy on earth. It radiates about 27×1023 KW energy each second. The average solar energy received by earth every second per 1 sq. meter  is called solar constant and it is estimated to be nearly 1. 4 KWm^-2.  Different types of energy sources in our daily life are the changed forms of solar energy directly or indirectly. Green plants uses sun light to produce food by photosynthesis process. The food produced by plants is consumed by different types of animals to produce energy for their growth and development. Wind blows in the earth's atmosphere due to change in temperature caused by solar energy that helps to run the wind mills and wind turbines. Water cycle maintained by solar energy recharges the under ground water and irrigates the land, runs the electric turbines in hydropower stations. Most of the energy sources that we use today like fossil fuels, bio-fuel, hydroelectricity, tidal energy etc. are dependent upon solar energy directly or indirectly, so, sun is the main source of energy.  

Energy crisis: 
The rate of consumption of the fuel energy is so rapid that they can not last for longer time due to population growth. If the rate of consumption of fuel energy is continuously increases and no other alternative souses of energy are searched, the fuel like petrol, coal diesel, coal, will be finished. This results the world to be in serous problem of energy scarcity. This shortage of energy sources is called energy crisis.

The main causes of energy crisis are:
i. Huge demand of energy sources because of over population.
ii. lack of proper management of non-renewable source of energy.
iii. Over use of non-renewable source of energy.

Ways to solve energy crisis:
i. By using alternative source of energy.
ii. By controlling population growth.
iii. By conserving the existing source of energy.
iv. By proper management of non-renewable source of energy.

Conservation of energy: 
The saving of energy by proper management and utilization to stop the energy crisis is called conservation of energy. Energy can be conserved in the following ways:
i. by using alternative sources of energy.
ii. by promoting the devices which utilize the solar energy, hydro-power, wind energy, tidal energy etc.
iii. by avoiding non-renewable sources of energy as much as possible.

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