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General Science: Sources of Energy (Physics)
📅 Date: 14 February 2026 (Saturday)
This chapter is critical for the cbse . students must understand Sustainable Development, Energy Security, and Pollution Control. Exams often ask questions related to renewable energy targets, the specific composition of fuels (like Biogas or CNG), and the science behind nuclear power. Let us dissect this chapter with the depth and precision required for a top-tier score.
1. The Fundamental Energy Paradox
Concept: We learned in the Law of Conservation of Energy that energy cannot be created or destroyed. So, why do we have an "Energy Crisis"?
The Dissipation of Energy: While total energy remains constant, usable energy is constantly converted into unusable energy.
- Example: When a candle burns, chemical energy turns into heat and light. You cannot collect that heat and light to recreate the wax. The energy has "dissipated" into the environment.
Conclusion: Because energy degrades from a concentrated form (useful) to a dispersed form (useless heat), we constantly need new sources to replenish our supply.
2. What Defines a "Good" Source of Energy?
In a preliminary exam, you might get a question asking which of the following is not a characteristic of a good fuel. You must know the criteria:
- High Calorific Value: It should produce a large amount of heat per unit mass.
- Accessibility: It should be easily available.
- Transport & Storage: Safe and easy to move.
- Economical: Cost-effective.
- Burn Rate: Moderate rate (not explosive, not too slow).
- Cleanliness: Minimal smoke and low residue (ash).
3. Conventional Sources of Energy (The Old Guard)
These are sources we have been using for a long time. They are generally non-renewable.
A. Fossil Fuels (Coal, Petroleum, Natural Gas)
Formed from the decomposition of biomass buried under the earth millions of years ago.
- Non-Renewable: They are exhaustible.
- Air Pollution: Releases oxides of Carbon, Nitrogen, and Sulphur (COx, NOx, SOx).
- Acid Rain: Oxides of Sulphur and Nitrogen dissolve in rain to form acids.
- Greenhouse Effect: CO2 traps heat, leading to Global Warming.
B. Thermal Power Plants
The Mechanism: Fossil fuels burn → Boil water → High-pressure Steam → Turns Turbine → Turns Generator → Electricity.
Location Strategy: Usually built near coal/oil fields because transmitting electricity is cheaper than transporting tons of coal.
Conversion: Chemical → Heat → Mechanical → Electrical Energy.
C. Hydro Power Plants (Dams)
India meets approx. 25% of its energy needs through Hydroelectricity.
Mechanism: Dams block rivers → Water level rises (Potential Energy increases) → Water released → Turns Turbine (Kinetic Energy) → Electricity.
- Methane Emission: Submerged vegetation rots anaerobically (without oxygen), releasing massive amounts of Methane (CH4), a potent greenhouse gas.
- Ecosystem Destruction: Forest/agricultural land submerged.
- Displacement: Human settlements forced to relocate (e.g., Tehri, Sardar Sarovar).
4. Improvements in Conventional Technology
A. Biomass and Charcoal
The Solution - Charcoal: When wood is burnt in a limited supply of oxygen, water and volatile materials are removed.
Benefit: Burns without flame, is smokeless, and has higher heat generation efficiency than wood.
B. Bio-gas (Gobar Gas) – Star Topic
The most efficient way to use cow dung via Anaerobic Decomposition in a "Digester" tank.
- Methane (CH4): Up to 75% (Main fuel component).
- Other Gases: CO2, Hydrogen, Hydrogen Sulphide.
- Benefits: Clean fuel, high heat, and the leftover slurry is nitrogen-rich manure.
C. Wind Energy
Kinetic energy of wind rotates blades → Turbine → Generator.
Constraints:
- Minimum Speed: Wind speed must be greater than 15 km/h.
- Land Use: Requires vast land (2 hectares per 1 MW).
5. Alternative / Non-Conventional Sources
A. Solar Energy
- Solar Cooker: Uses Black Surface (absorbs heat), Glass Sheet (Greenhouse effect), and Concave Mirrors (focus sunlight).
- Solar Cells (Photovoltaics): Convert Solar Energy directly to Electricity.
- Material: Silicon (Semiconductor).
- Connectivity: Cells connected using Silver wire (best conductor).
B. Energy from the Sea
- Tidal Energy: Caused by the gravitational pull of the Moon.
- Wave Energy: Traps kinetic energy of waves.
Principle: Temperature difference between warm surface and cold deep water.
Critical Condition: Temperature difference must be 20°C (293 K) or more between surface and 2 km depth.
Working: Warm water boils a volatile liquid like Ammonia (NH3) to turn the turbine.
C. Geothermal Energy
Molten rocks (Magma) push up into "Hot Spots". Underground water touches these spots → Steam → Turbines.
Locations in India: Manikaran (Himachal) and Puga Valley (Ladakh).
6. Nuclear Energy (The Power of the Atom)
The Einstein Equation: E = Δmc2 (Energy = Mass Defect × Speed of Light squared).
A tiny amount of mass is destroyed to create massive energy.
1. Nuclear Fission ("Splitting")
- Action: Heavy nucleus (Uranium-235, Plutonium) bombarded with low-energy neutrons splits into lighter nuclei.
- Examples: Nuclear Power Plants, Atom Bomb.
- Risk: Radioactive leakage and waste storage.
- Action: Two light nuclei (Hydrogen isotopes) fuse to form a heavier nucleus (Helium).
- Condition: Requires extreme temperature and pressure.
- Examples: The Sun/Stars, Hydrogen Bomb.
7. Environmental Consequences & Sustainability
- CNG (Compressed Natural Gas): Cleaner than petrol but still produces CO2.
- Hydrogen: The cleanest fuel. Burning it produces only Water (H2O). Used in rockets.
- Renewable: Solar, Wind, Tide, Geothermal, Hydro.
- Non-Renewable: Fossil fuels, Nuclear fuels (Uranium is finite).
8. Mentor’s Final Drill (Exam-Ready Questions)
A: The Sun. (Exception: Geothermal and Nuclear energy do not originate from the Sun).
Q: Why is the glass plate important in a solar cooker?
A: It traps the heat radiation (Infrared) inside the box, creating a Greenhouse Effect.
Q: Which gas is evolved when vegetation rots under water in dams?
A: Methane (a greenhouse gas).
Q: What is the primary cause of acid rain?
A: Oxides of Sulphur and Nitrogen released by burning fossil fuels.
Q: In an OTEC plant, what is used as the working fluid?
A: A volatile liquid like Ammonia (NH3).
Q: Why is charcoal considered a better fuel than wood?
A: It has a higher calorific value, burns without smoke, and leaves no residue.
Action Plan: Memorize the numerical limits: Wind (>15 km/h) and OTEC (>20°C). Be clear on Biogas composition (Methane) and the difference between Fission (Reactor) and Fusion (Sun). You have now completed the entire Physics and Energy module!