Class 10 Science Notes Chapter 14 (Sources of energy) – Science Book

Detailed Notes with MCQs of Chapter 14, 'Sources of Energy'. This is a crucial chapter, not just for your board exams but also frequently touched upon in various government exams. We need to understand where our energy comes from, the pros and cons of each source, and why we're looking for alternatives.

Energy: The Basics

• Energy: The capacity to do work. It exists in various forms (heat, light, mechanical, electrical, chemical, nuclear).
• Law of Conservation of Energy: Energy can neither be created nor destroyed; it can only be transformed from one form to another.
• Source of Energy: Any system or material from which usable energy can be extracted.

Characteristics of a Good Source of Energy:

A good source of energy should ideally:

1. Have a high calorific value (release a large amount of energy per unit mass or volume).
2. Be easily accessible and available in sufficient quantity.
3. Be easy to store and transport.
4. Be economical (cost-effective).
5. Be safe to handle and use.
6. Cause minimal environmental pollution.
   (Note: No single source perfectly meets all these criteria)

Classification of Energy Sources:

Detailed Notes on Energy Sources:

1. Conventional Sources of Energy

• A. Fossil Fuels:

  • Formation: Formed over millions of years from the buried remains of dead plants and animals under high pressure and temperature.
  • Types: Coal, Petroleum (Crude Oil), Natural Gas.
  • Advantages:
    • High energy density (high calorific value).
    • Relatively easy to extract, transport, and use (established technology).
    • Foundation of modern industrialization.
  • Disadvantages:
    • Non-renewable: Finite reserves, being depleted rapidly.
    • Pollution:
      • Burning releases oxides of carbon (CO, CO2 - greenhouse gas), nitrogen (NOx), and sulfur (SOx - acid rain).
      • Particulate matter (soot) causes respiratory problems.
    • Extraction impacts: Habitat destruction, land subsidence.
  • Improving Efficiency: Technologies like fluidized bed combustion in thermal power plants aim to reduce pollution. Controlling emissions through scrubbers and electrostatic precipitators.
  • Thermal Power Plants: Burn fossil fuels (mainly coal) to heat water, produce steam, which turns turbines connected to generators to produce electricity. Major source of air pollution.

• B. Hydro Power:

  • Principle: Converts the potential energy of stored water (in dams) into kinetic energy (falling water), which turns turbines to generate electricity.
  • Advantages:
    • Renewable (depends on the water cycle).
    • Pollution-free during operation (no emissions).
    • Can control floods and provide water for irrigation.
    • Long operational life.
  • Disadvantages:
    • High initial cost and long construction time.
    • Requires specific geographical locations (hilly terrain, river).
    • Ecological Impact: Submerges large areas of land (forests, agricultural land), destroys habitats.
    • Social Impact: Displaces large populations.
    • Affects aquatic life downstream.
    • Decomposition of submerged vegetation releases methane (a greenhouse gas).

• C. Biomass:

  • Definition: Organic matter derived from plants and animals (e.g., wood, agricultural waste, animal dung, sewage).
  • Traditional Use (Wood, Cow Dung Cakes):
    • Disadvantages: Low calorific value, produce a lot of smoke (air pollution), low efficiency, deforestation (wood).
  • Improved Methods:
    • Charcoal: Produced by heating wood in a limited supply of air. Burns without flames, is relatively smokeless, and has a higher calorific value than wood.
    • Biogas (Gobar Gas):
      • Process: Anaerobic decomposition (breakdown by bacteria in the absence of oxygen) of cow dung, sewage, crop residues, etc., in a biogas plant.
      • Composition: Mainly Methane (CH4, up to 75%), Carbon Dioxide (CO2), Hydrogen (H2), Hydrogen Sulphide (H2S).
      • Biogas Plant Structure: Inlet (for slurry), Digester (airtight tank where decomposition occurs), Outlet (for spent slurry), Gas Tank/Dome (collects biogas), Gas Outlet pipe.
      • Advantages: Excellent fuel (high calorific value, burns without smoke), produces valuable manure (spent slurry rich in nitrogen and phosphorus), safe waste disposal method, reduces spread of diseases.

• D. Wind Energy:

  • Principle: Kinetic energy of moving air (wind) is used to rotate large blades of a windmill/wind turbine, which drives a generator to produce electricity.
  • Advantages:
    • Renewable.
    • Environmentally friendly (no emissions during operation).
    • Low running cost once installed.
  • Disadvantages:
    • Requires consistent high wind speeds (typically > 15 km/h).
    • Large land area needed for wind farms.
    • High setup cost.
    • Variable energy output (depends on wind).
    • Noise pollution from turbines.
    • Visual impact on landscape.
    • Potential hazard to birds.
  • Wind Farms: Large number of windmills erected over a large area. Output from multiple turbines is coupled together.
  • Note: Denmark is often called the 'country of winds' due to its significant wind energy utilization. India has large wind farms, especially in Tamil Nadu, Gujarat, Maharashtra.

2. Non-Conventional (Alternative) Sources of Energy

• A. Solar Energy:

  • Source: Energy radiated by the Sun.
  • Solar Constant: Approx. 1.4 kJ per second per square meter (or 1.4 kW/m²) just outside the Earth's atmosphere. Varies slightly and is reduced by the atmosphere.
  • Devices:
    • Solar Cooker (Box Type): Insulated box, painted black inside, covered with a glass sheet. A plane mirror reflector increases incident radiation. Works on the greenhouse effect (glass traps heat) and black surface absorption. Limitations: Slow cooking, cannot be used at night or on cloudy days, cannot be used for frying/baking.
    • Solar Concentrators: Use curved reflectors (parabolic) or lenses to focus sunlight onto a small area, achieving higher temperatures (used in solar furnaces, some power generation).
    • Solar Cells (Photovoltaic Cells - PV Cells): Convert sunlight directly into electricity (photovoltaic effect). Made primarily of silicon (special grade). A single cell produces low voltage/power; hence, cells are combined into solar panels.
      • Advantages: No moving parts, low maintenance, suitable for remote/inaccessible areas, environmentally friendly operation.
      • Disadvantages: High manufacturing cost (special grade silicon is expensive, silver used for interconnection), lower efficiency compared to other methods, requires storage (batteries) for continuous supply, requires large area for significant power generation.
      • Uses: Calculators, watches, street lighting, traffic signals, water pumps, artificial satellites, space probes, radio/TV relay stations.
    • Solar Water Heater: Insulated box with black-painted pipes/surface through which water flows. Uses solar heat to warm water.

• B. Energy from the Sea:

  • Tidal Energy:
    • Principle: Uses the energy associated with the rise and fall of ocean water levels (tides) due to gravitational pull of the moon and sun.
    • Harnessing: A dam (barrage) is built across a narrow opening to the sea. During high tide, water flows into the reservoir and turns turbines. During low tide, stored water flows out, again turning turbines.
    • Limitations: Very few suitable sites globally where the tidal range is high enough; variable output.
  • Wave Energy:
    • Principle: Uses the kinetic energy of powerful ocean waves.
    • Harnessing: Various devices designed to capture wave motion (e.g., oscillating water columns, floating devices) to drive turbines.
    • Limitations: Variable energy output (depends on wave strength), difficult to build robust devices to withstand storms, currently expensive.
  • Ocean Thermal Energy Conversion (OTEC):
    • Principle: Exploits the temperature difference (ΔT) between warm surface water and cold deep ocean water (needs ΔT ≥ 20°C over a depth of ~1000 m).
    • Harnessing: Warm surface water is used to boil a volatile liquid (like ammonia or CFCs). The vapour drives a turbine. Cold deep water is pumped up to condense the vapour back into liquid.
    • Limitations: Low efficiency, high capital and maintenance costs (corrosion), limited suitable locations.

• C. Geothermal Energy:

  • Source: Heat energy from the molten rocks (magma) in the Earth's interior.
  • Geothermal Hotspots: Regions where magma is closer to the Earth's surface. Underground water comes in contact with these hotspots, gets heated, and turns into steam.
  • Harnessing: Steam is trapped in rocks. Wells are drilled, and the steam is piped out at high pressure to turn turbines and generate electricity. Sometimes hot water is directly used for heating.
  • Advantages: Relatively clean (low emissions compared to fossil fuels), reliable (continuous source).
  • Disadvantages: Limited suitable locations (hotspots), high cost of drilling, potential release of dissolved gases (like H2S).
  • Examples: Power plants operational in New Zealand, USA. Some potential sites in India (e.g., Puga Valley in Ladakh, Manikaran in Himachal Pradesh).

• D. Nuclear Energy:

  • Source: Energy released when the nucleus of an atom is altered (split or fused). E = mc² (Einstein's mass-energy equivalence).
  • Nuclear Fission:
    • Process: The nucleus of a heavy atom (like Uranium-235, Plutonium-239) is bombarded with a low-energy (slow) neutron. It splits into smaller nuclei, releasing a tremendous amount of energy and 2-3 more neutrons. These neutrons cause further fissions, leading to a chain reaction.
    • Nuclear Reactor: A device where a controlled nuclear fission chain reaction takes place to produce heat. This heat is used to produce steam and generate electricity (Nuclear Power Plant). Requires moderators (like heavy water, graphite) to slow down neutrons and control rods (like cadmium, boron) to absorb excess neutrons and control the reaction rate.
    • Fuel: Commonly Uranium (U-235).
    • Advantages: Huge amount of energy released from a small amount of fuel, no greenhouse gas emissions during operation.
    • Disadvantages:
      • Nuclear Waste: Produces highly radioactive byproducts that remain hazardous for thousands of years. Safe storage and disposal is a major challenge.
      • Risk of Accidents: Accidental leakage of radiation can have devastating long-term environmental and health consequences (e.g., Chernobyl, Fukushima).
      • High Costs: Very high cost of building, maintaining, and decommissioning nuclear power plants due to safety requirements.
      • Limited Fuel: Natural Uranium contains only about 0.7% fissionable U-235.
      • Risk of misuse for weapons.
  • Nuclear Fusion:
    • Process: Two or more light nuclei (like isotopes of hydrogen - Deuterium (²H) and Tritium (³H)) fuse together at extremely high temperatures and pressures to form a heavier nucleus (like Helium), releasing even more energy than fission. This is the process powering the Sun and stars.
    • Advantages (Potential): Abundant fuel source (Deuterium from seawater), produces less radioactive waste compared to fission, inherently safer (reaction stops if conditions aren't met).
    • Disadvantages: Requires extremely high temperatures (millions of °C) and pressures, making it very difficult to initiate and sustain a controlled reaction. Currently not commercially viable for power generation (research ongoing, e.g., ITER project).

3. Environmental Consequences

• Burning fossil fuels causes air pollution, acid rain, and contributes significantly to global warming (greenhouse effect).
• Hydroelectric projects cause large-scale ecological and social disruption.
• Nuclear energy poses risks of radiation leakage and the challenge of waste disposal.
• Even 'clean' sources like wind and solar have impacts (land use, manufacturing processes, visual impact).
• No energy source is completely impact-free. The choice involves balancing energy needs with environmental protection.

4. How Long Will Energy Sources Last? (Energy Crisis)

• Fossil fuels are finite and being consumed much faster than they are formed. Estimates suggest current reserves might last only a few decades (oil, gas) to a couple of centuries (coal) at present consumption rates.
• This necessitates:
  • Energy Conservation: Reducing energy consumption through efficient practices and technologies (e.g., using energy-efficient appliances, public transport, turning off lights/fans).
  • Shift to Renewable/Sustainable Sources: Increasing reliance on solar, wind, geothermal, etc., which are practically inexhaustible and generally less polluting.

Multiple Choice Questions (MCQs):

1. Which of the following is a non-renewable source of energy?
   (a) Wind Energy
   (b) Solar Energy
   (c) Coal Energy
   (d) Tidal Energy

2. The main component of Biogas is:
   (a) Methane
   (b) Carbon Dioxide
   (c) Hydrogen Sulphide
   (d) Nitrogen

3. In a hydroelectric power plant:
   (a) Kinetic energy is converted into potential energy.
   (b) Potential energy of stored water is converted into electricity.
   (c) Heat energy is converted into electricity.
   (d) Chemical energy is converted into electricity.

4. Which phenomenon is utilized in a box-type solar cooker?
   (a) Photovoltaic effect
   (b) Nuclear fission
   (c) Greenhouse effect
   (d) Electromagnetic induction

5. Nuclear energy is generated through:
   (a) Chemical reactions
   (b) Nuclear fission and fusion
   (c) Burning of uranium
   (d) Anaerobic decomposition

6. Which of the following is a major disadvantage of building large dams for hydroelectric power?
   (a) Production of acid rain
   (b) High air pollution during operation
   (c) Submergence of large land areas and displacement of people
   (d) Depletion of fossil fuels

7. Solar cells are primarily made of:
   (a) Copper
   (b) Silicon
   (c) Aluminium
   (d) Carbon

8. OTEC power plants require a temperature difference between surface water and deep ocean water of at least:
   (a) 5°C
   (b) 10°C
   (c) 15°C
   (d) 20°C

9. Which of the following is NOT an environmental consequence of using fossil fuels?
   (a) Acid rain
   (b) Greenhouse effect
   (c) Radioactive waste generation
   (d) Air pollution (SOx, NOx, particulates)

10. A good source of energy should have:
    (a) Low calorific value and high pollution
    (b) High calorific value and easy accessibility
    (c) Difficult storage and transportation
    (d) High cost and limited availability

Answer Key for MCQs:

1. (c)
2. (a)
3. (b)
4. (c)
5. (b)
6. (c)
7. (b)
8. (d)
9. (c) (Radioactive waste is associated with Nuclear Energy)
10. (b)

Make sure you revise these points thoroughly. Understanding the principles, advantages, and disadvantages of each source is key for your exams. Good luck!