Description of the units and scale of energy

Description:

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Unit of Energy

The SI unit of energy is the Joule (J), named after the English physicist James Prescott Joule.

1 Joule is defined as the work done when a force of one Newton is applied to an object and the object is displaced by 1 metre in the direction of the applied force:

$1 J = 1 N·m = 1 kg·m^{2}·s^{-2}$

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Other Common Units of Energy

Unit	Symbol	Equivalent in Joules	Used In
Electronvolt	eV	$1.6 × 10^{-19} J$	Atomic & nuclear physics
Calorie	cal	$4.184 J$	Thermodynamics, food
Kilocalorie	kcal	$4184 J$	Nutrition
Kilowatt-hour	kWh	$3.6 × 10^{6} J$	Electrical energy
Erg	erg	$10^{-7} J$	CGS system
British Thermal Unit	BTU	$1055 J$	Engineering (UK/US)

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Scale of Energy — From Smallest to Largest

Scale	Energy (Joules)	Example
$10^{-34} J$	Quantum scale	Energy of a photon of a radio wave
$10^{-19} J$	Atomic scale	1 electronvolt (ionisation energy)
$10^{-18} J$	Molecular scale	Energy of a chemical bond
$10^{-3} J$	Millijoule	Energy in SHM of a spring (small oscillation)
$1 J$	Joule	KE of a 1 kg mass moving at √2 m/s
$10^{3} J$	Kilojoule	Energy in a food biscuit
$10^{6} J$	Megajoule	Energy of a 1-tonne car at 160 km/h
$10^{9} J$	Gigajoule	Daily energy use of a household
$10^{15} J$	Petajoule	Energy released by a small nuclear bomb
$10^{22} J$	Astronomical scale	Kinetic energy of Earth's rotation
$10^{41} J$	Stellar scale	Energy released by a supernova explosion

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Renewable Energy Sources

Renewable Energy Sources:

Various renewable energy sources are as follows:

Solar Energy:

The solar energy is a non conventional energy source. It is very cost effective clean and non polluted renewable energy source and reduces the greenhouse gas effect.

The Solar Energy is derived from the Sun radiation and can be utilised by photosynthesis, photo voltaic cell, photo thermoelectric system.

The sun release the enormous amount of energy and it's rate of radiation is $3.7 \times 10^{20}$ megawatt while the earth receive the radiation at rate by $1.85 \times 10^{11}$ megawatt. So energy radiation by the sun is several times more than the consumption of radiation in the earth.

Advantages:

1.) It is very clean energy.

2.) It is non polluted energy source.

3.) It is zero cost energy source and low maintenance cost.

4.) It has zero noise in operation.

Disadvantages :

1.) Energy source cannot utilise properly at night, cloudy atmosphere and rainy day.

2.) It has required large surface area to collect the energy source from Sun.

Hydro energy:

The hydro energy is derived from moving and falling water which convert into mechanical energy and utilise for production of electrical energy through turbine.

The water is stored in reservoir or dam has high potential energy and when water flow or fall under the gravity then it rotate the turbine and produces the electricity.

Advantages:

1.) It is very clean energy source.

2.) It produce zero pollution.

3.) It has zero fuel cost.

4.) It requires low maintenance cost.

5.) It is reliable energy source.

Disadvantages:

1.) It can cause climate change due to high amount of storage of water in mountains.

2.) It can cause flood and disrupt ecosystem.

Wind energy:

Wind energy is also non polluting energy source and it has tremendous potential to fulfill the demand of energy of the country.

It is estimated that only $2 \%$ of solar energy fall on the earth and converted into kinetic energy of the atmospheric molecules or atoms. The highest kinetic energy of atmosphere is found in the lower to mid troposphere layer which is lowest layer of atmosphere because of that this kinetic energy can be easily converted to the mechanical energy which can futher utilise for the production of electrical energy and other energy production.

Advantage:

1.) It is useful for remote places for the production of electricity.

2.) The availability of the source is zero cost.

Disadvantages:

1.) This energy source cannot be properly utilised where wind is available at very higher location.

2.) It is unreliable because flow of wind cannot be continuous all the time.

Wave Energy:

The wave energy is available on the surface of sea. The floating propeller is placed on the surface of the shallow water near to shores and due to motion of wave propeller get start to rotate and this rotational energy is used to derive the turbines.

Advantages:

1.) This is clean or cheap energy source.

2.) The size of the machine for the collection of wave is comparatively smaller than solar device.

Disadvantages:

Corrrosion of material used in plant.

Geothermal energy:

This is the energy is produced due to hot rocks present inside the earth. The temperature of the earth increases with increase in depth below the surface of the earth. The hot molted rock is present at center or core of the earth this causes volcano action. The hot rock is pull out from volcano and used to produce the steam by heating water. This steam is further utilised for the operation of turbine to produce the electricity.

Advantages:

It is cheap source which requires small area for the operation or production of the electricity.

Disadvantages:

1.) It causes the air pollution due to production of gases like $H_{2}S$ and $NH_{3}$in steam waste.

2.) It is also causes noise pollution due to drilling operation.

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Basics of Third Generation Solar Cells and Their Types

Third Generation Solar Cells :

They are proposed to be very different from the previous semiconductor devices as they do not rely on a traditional p-n junction to separate photogenerated charge carriers.

For space applications quantum well devices (quantum dots, quantum ropes etc.) and devices incorporating carbon nanotubes are being studied with a potential for up to $45 %$ production efficiency.

For terrestrial applications, these new devices include photoelectrochemical cells, polymer solar cells, nanocrystal solar cells,dye sensitized solar cells and are still in the research phase.

Types of Third Generation Solar Cells :

A.) Organic Photovoltaic Cell :

1. The solar cells based on organic semiconductor can provide a low cost alternative for photovoltaic solar.

2. The thickness of the active layer of organic solar cells is only $100 nm$ thin, which is about $1000$ times thinner than the crystalline silicon solar cells, and it is about 10 times thinner than the current inorganic thin film solar cells.

3. In the low material consumption per solar cell and the relatively simpler cell processing of organic semiconductors, there is a large potential for low cost large area solar cells.

4. Due to this reason, there is a considerable interest in organic photovoltaic devices.

5. Their principal advantage is that they are flexible and can bend without breaking, unlike $Si$, which is brittle.

6. They are also very light and cheap.

7. They may folded or cut into required size and can still be used.

B.) Dye Sensitized Solar Cell (DSSC):

1. Dye Sensitized Solar Cell converts any visible light into electrical energy.

2. The dye sensitized solar cells can be considered as a thin film solar cell device. This technology is not yet commercialized but is on the verge of commercialization.

3. The dye sensitized solar cells can be made flexible. It has a very good potential for being a low cost effect solar cell technology.

4. This is mainly possible because of the large availability and low cost of the ingredient material as well as due to the low processing temperatures.

5. The dye sensitized solar cells is a photo-electro-chemical device. In its operation it involves a photon, an electron and a chemical reaction.

6. The operation of dye sensitized solar cell is considered similar to that of a photosynthesis process.

7. The DSSC has a number of attractive features; it is simple to make using conventional roll-printing techniques, is semi-flexible and semi- transparent which offers different type of uses not applicable to glass-based systems, and cost of most of the materials used in DSSC are very low.

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Safety measures for nuclear power plants

Safety measures for nuclear power plants are as follows:

1.) A nuclear power plant should bė constructed away from human habitation. The 106 km radius around the plant should be excluded zone where no public habitation is permitted.

2.) The materials to be used for the construction of a nuclear power plant should be of required standards.

3.) The nuclear power plant produces the waste water that should be purified.

4.)The nuclear power plant must be provided with such a safety system which should safely shut down the plant as and when necessity arises.

5.) There must be periodic checks tó ensure that radioactivity does not exceed the permissible value in the environment.

6.) While disposing off the wastes from the nuclear plants it shoud be where these ensured that there is no pollution of water of river or sea wastes are disposed. Nuclear power plants follow a multi-layered safety approach called defense in depth. This ensures that even if one system fails, multiple backup systems continue to protect people and the environment.

🔒 1. Physical Barriers

Radioactive materials are confined within several protective layers:

Fuel pellets: Solid ceramic form of uranium

Fuel rod cladding: Prevents leakage of radioactive gases

Reactor pressure vessel: Thick steel container

Containment building: Reinforced concrete dome

👉 These layers act as successive shields, preventing radiation release.

⚙️ 2. Reactor Control Systems

Control rods absorb neutrons to regulate the chain reaction

In emergencies, a SCRAM (rapid shutdown) inserts rods fully

Sensors continuously monitor:

Temperature

Pressure

Power levels

Radiation

👉 Ensures the reactor remains stable under all conditions.

❄️ 3. Cooling Systems

Removes heat from the reactor core

Includes:

Primary loop (direct cooling of core)

Secondary loop (steam generation for turbines)

Emergency Core Cooling System (ECCS)

👉 Prevents overheating and core meltdown.

🔋 4. Backup Power Supply

Multiple diesel generators and battery systems

Automatically activate during power failure

👉 Critical for maintaining cooling and monitoring systems.

🧱 5. Containment and Shielding

Thick steel + concrete structures

Designed to withstand:

Earthquakes

Aircraft impact

Internal pressure

👉 Protects both workers and the environment.

🧠 6. Safety Culture & Human Factors

Highly trained operators

Strict operating procedures

Team-based verification

👉 Human reliability is as important as technology.

📡 7. Monitoring & Emergency Systems

Continuous radiation monitoring (inside & outside plant)

Automatic alarms and shutdown systems

Emergency preparedness:

Evacuation zones

Public communication plans

👉 Ensures rapid response in abnormal situations. 🏛️ 8. Regulatory Oversight Governed by national authorities and international bodies like the International Atomic Energy Agency Includes: Regular inspections Safety audits Stress testing 👉 Guarantees compliance with strict safety standards. 🔄 9. Passive Safety Features (Modern Reactors) Operate without electricity or human intervention Examples: Gravity-fed cooling Natural convection systems 👉 Adds an extra layer of reliability, especially during emergencies. ☢️ 10. Waste Management Safety

Spent fuel stored in: Cooling pools Dry cask storage Long-term disposal in deep geological repositories 👉 Prevents environmental contamination.

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