Class 10 Notes

Class 10 Science Notes Chapter 14 (Chapter 14) – Examplar Problems (English) Book

Philoid

Philoid

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Examplar Problems (English)
Detailed Notes with MCQs of Chapter 14, 'Sources of Energy', from your NCERT Exemplar book. This chapter is crucial not just for your board exams but also forms a basis for many questions in government exams where general science is a component. Pay close attention.

Chapter 14: Sources of Energy - Detailed Notes for Exam Preparation

1. What is Energy?

  • Energy is the capacity to do work.
  • We need energy for all life processes and activities (running machines, cooking, lighting, transport, industry, etc.).
  • The Law of Conservation of Energy states that energy can neither be created nor destroyed; it can only be transformed from one form to another. However, during transformation, some energy is often lost to the surroundings in less usable forms (like heat).

2. What Makes a Good Source of Energy?
A good source of energy should ideally be:

  • High Calorific Value: Provides a large amount of energy per unit mass or volume.
  • Easily Accessible: Readily available.
  • Easy to Store and Transport: Convenient to handle.
  • Economical: Affordable.
  • Controllable: Release of energy can be started or stopped as needed.
  • Safe to Handle: Minimal risk involved in usage.
  • Low Environmental Pollution: Causes minimal damage to the environment.
    (Note: No single source possesses all these qualities perfectly.)

3. Classification of Energy Sources:

  • Based on Usage/Tradition:
    • Conventional Sources: Commonly used for a long time, well-established technology. Examples: Fossil fuels (coal, petroleum, natural gas), Hydro energy, Biomass (firewood, dung cakes), Wind energy (in some contexts).
    • Non-Conventional (Alternative) Sources: Developed more recently to reduce dependence on conventional sources and mitigate environmental impact. Examples: Solar energy, Geothermal energy, Nuclear energy, Energy from the sea (Tidal, Wave, OTEC).
  • Based on Regeneration:
    • Renewable Sources: Can be replenished naturally within a human lifespan or are practically inexhaustible. Examples: Solar energy, Wind energy, Hydro energy, Geothermal energy, Biomass (if managed sustainably), Ocean energy.
    • Non-Renewable Sources: Exist in finite quantities and are consumed much faster than they are formed (millions of years). Examples: Fossil fuels (coal, petroleum, natural gas), Nuclear fuels (like Uranium).

4. Conventional Sources of Energy - In Detail

  • Fossil Fuels:

    • Formation: Formed over millions of years from the buried remains of ancient plants and animals under high pressure and temperature.
    • Types: Coal, Petroleum (Crude Oil), Natural Gas.
    • Advantages: High calorific value, extensive infrastructure exists for extraction and use.
    • Disadvantages:
      • Non-renewable: Finite reserves, will eventually run out.
      • Pollution: Burning releases oxides of carbon (CO2 - greenhouse gas), nitrogen, and sulfur (SO2, NOX - cause acid rain), particulate matter (ash, smoke).
      • Greenhouse Effect: CO2 traps heat, leading to global warming and climate change.
      • Acid Rain: Oxides of sulfur and nitrogen dissolve in rainwater, harming ecosystems, buildings, and soil.
    • Improving Efficiency: Technologies like fluidized bed combustion can reduce emissions from coal power plants. Using CNG (Compressed Natural Gas) in vehicles reduces pollution compared to petrol/diesel.

  • Thermal Power Plants:

    • Working: Burn fossil fuels (mainly coal) to heat water, producing high-pressure steam. This steam rotates a turbine, which drives a generator to produce electricity.
    • Efficiency: Typically low (around 30-40%), significant energy lost as heat.
    • Location: Often located near coal fields or water sources to minimize transportation costs and ensure cooling water availability.
    • Pollution: Major source of air pollution (ash, SO2, NOX, CO2) and thermal pollution of water bodies.

  • Hydro Power Plants:

    • Working: Use the potential energy of water stored behind a dam. Water flows down through pipes (penstock), rotating turbines connected to generators.
    • Advantages: Renewable source (depends on water cycle), no pollution during operation, long lifespan, useful for flood control and irrigation.
    • Disadvantages:
      • High Initial Cost & Time: Building dams is expensive and time-consuming.
      • Ecological Impact: Submerges large areas of land (forests, agricultural land), destroys habitats, affects aquatic life migration.
      • Social Impact: Displaces large populations (rehabilitation issues).
      • Site Specific: Requires suitable terrain (hilly areas) and water availability.
      • Methane Emission: Decomposition of submerged vegetation can release methane (a potent greenhouse gas).

  • Biomass Energy:

    • Definition: Energy derived from organic matter (plants and animal waste).
    • Traditional Fuels: Firewood, Cow-dung cakes, Crop residues.
    • Disadvantages (Traditional):
      • Low calorific value.
      • Produce a lot of smoke (air pollution, respiratory diseases).
      • Low efficiency.
      • Deforestation (if firewood use is unsustainable).
      • Loss of valuable manure (when dung cakes are burnt).
    • Improvements:
      • Charcoal: Burning wood in limited oxygen supply produces charcoal, which burns cleaner and has a higher calorific value than wood.
      • Biogas: See below.

  • Biogas (Gobar Gas):

    • Production: Anaerobic decomposition (breakdown in the absence of oxygen) of organic matter (cow dung, sewage, crop residues, vegetable waste) by microorganisms in a biogas plant (digester).
    • Composition: Mainly Methane (CH4, up to 75%), Carbon Dioxide (CO2), Hydrogen (H2), Hydrogen Sulphide (H2S).
    • Working of Plant: Slurry (dung + water) fed into digester; anaerobic bacteria decompose it, producing biogas collected in a gas tank/dome; spent slurry removed and used as excellent manure (rich in nitrogen and phosphorus).
    • Advantages:
      • Excellent fuel (high calorific value, burns without smoke).
      • Clean energy source.
      • Waste disposal method.
      • Produces high-quality manure.
      • Relatively simple technology.

  • Wind Energy:

    • Source: Uneven heating of the Earth's surface by the sun creates wind (kinetic energy of moving air).
    • Working: Windmills convert the kinetic energy of wind into rotational energy. This rotation can be used directly (e.g., grinding grain, pumping water) or to turn a turbine connected to a generator (producing electricity in wind farms).
    • Wind Farm: A large number of windmills installed over a large area.
    • Advantages: Renewable, environmentally clean (no emissions during operation), low running cost.
    • Disadvantages:
      • Wind Speed Requirement: Requires average wind speeds > 15 km/h.
      • Land Requirement: Wind farms need large areas of land.
      • Site Specific: Only feasible in windy locations (coastal areas, open plains, mountain passes).
      • High Setup Cost: Initial investment is high.
      • Noise Pollution: Can be noisy.
      • Intermittent: Wind speed varies, leading to fluctuating power output (needs backup).
      • Hazard to Birds.
    • Potential in India: India has significant potential, especially in states like Tamil Nadu, Gujarat, Maharashtra, Rajasthan. Denmark is often called the 'country of winds'.

5. Non-Conventional Sources of Energy - In Detail

  • Solar Energy:

    • Source: Energy radiated by the Sun. India receives abundant solar energy.
    • Solar Constant: Approx. 1.4 kW/m² (energy received per unit area just outside Earth's atmosphere). Varies slightly. Amount reaching surface is less due to atmospheric absorption/scattering.
    • Devices:
      • Solar Cooker (Box-type): Insulated box, black interior surface (absorbs heat), glass sheet cover (traps heat via greenhouse effect), often a reflector mirror (increases incident radiation). Reaches 100-140 °C.
        • Advantages: Saves fuel, no pollution, retains nutrients in food.
        • Disadvantages: Slow cooking, cannot be used at night or on cloudy days, requires frequent adjustment towards the sun.
      • Solar Concentrators: Use curved reflectors (parabolic/spherical) to focus sunlight onto a small area, achieving much higher temperatures (used for community cooking, steam generation for electricity).
      • Solar Water Heater: Black painted pipes/surface absorb solar heat, transferring it to water flowing through them. Used for domestic/industrial hot water supply.
      • Solar Cells (Photovoltaic Cells - PV Cells): Convert sunlight directly into electricity (photovoltaic effect). Made of semiconductors (mainly Silicon). A single cell produces low voltage/power; cells are combined into solar panels for practical use.
        • Advantages: Direct conversion to electricity, no moving parts, low maintenance, suitable for remote/inaccessible areas, environmentally clean during operation.
        • Disadvantages: High manufacturing cost (though decreasing), lower efficiency (typically 15-25%), requires large area for significant power generation, electricity produced is DC (needs inverter for AC appliances), energy storage (batteries) needed for night/cloudy days, manufacturing process can involve hazardous materials.
        • Uses: Calculators, watches, street lighting, traffic signals, water pumps, artificial satellites, space probes.

  • Energy from the Sea:

    • Tidal Energy:
      • Source: Gravitational pull of the moon (mainly) and sun causes rise and fall of sea levels (tides).
      • Working: Dams (barrages) built across narrow openings to the sea. During high tide, water flows into the reservoir, turning turbines. During low tide, stored water flows out, again turning turbines.
      • Limitations: Few suitable sites worldwide where the tidal range is high enough; affects marine ecosystems.
    • Wave Energy:
      • Source: Kinetic energy of strong sea waves (generated by wind blowing over the sea).
      • Working: Various devices designed to trap the energy of oscillating waves to move air or hydraulic fluid, which then drives a turbine.
      • Limitations: Viable only where waves are consistently strong; devices must withstand harsh marine environments; variable power output.
    • Ocean Thermal Energy Conversion (OTEC):
      • Source: Temperature difference (ΔT) between warm surface water (heated by the sun) and cold deep ocean water.
      • Working: Requires ΔT ≥ 20 °C between surface and depths (up to 1000m). Warm surface water used to boil a volatile liquid (like ammonia or CFCs). The vapour drives a turbine. Cold deep water used to condense the vapour back to liquid.
      • Limitations: Low efficiency, high capital costs, corrosion issues, environmental concerns about pumping large volumes of water. Potential exists in tropical oceans.

  • Geothermal Energy:

    • Source: Heat from the Earth's interior (due to geological changes, radioactive decay). Molten rock (magma) heats underground water.
    • Geothermal Hotspots: Areas where this heat is close to the surface. Underground water comes in contact with hot rock, forming steam. This steam gets trapped between rocks at high pressure.
    • Working: Wells drilled into hotspots. Trapped steam released and used to rotate turbines connected to generators. Sometimes hot water is brought up and used directly for heating or flashed into steam.
    • Advantages: Clean energy (low emissions), reliable (continuous source), relatively low running costs.
    • Disadvantages: Few viable sites (specific geological conditions needed), drilling can be expensive and difficult, potential release of dissolved gases (like H2S), risk of triggering minor earthquakes in some areas.
    • Examples: New Zealand, USA have operational plants. In India, potential sites exist in Puga Valley (Ladakh) and Manikaran (Himachal Pradesh).

  • Nuclear Energy:

    • Source: Energy released during nuclear reactions (fission or fusion). Based on Einstein's mass-energy equivalence, E=mc².
    • Nuclear Fission:
      • Process: Splitting of a heavy nucleus (like Uranium-235, Plutonium-239) into smaller nuclei when bombarded with a low-energy neutron. Releases a tremendous amount of energy and more neutrons.
      • Chain Reaction: The released neutrons cause further fissions, leading to a self-sustaining chain reaction. This must be controlled in a reactor.
      • Nuclear Reactor: Device where controlled fission occurs. Fuel rods (Uranium), Moderator (slows down neutrons - e.g., heavy water, graphite), Control rods (absorb excess neutrons to control reaction rate - e.g., cadmium, boron), Coolant (transfers heat - e.g., water, liquid sodium), Shielding (prevents radiation leakage). Heat generated boils water -> steam -> turbine -> generator.
    • Advantages: Very high energy density (small amount of fuel produces huge energy), reliable power source (less dependent on weather), lower greenhouse gas emissions compared to fossil fuels (during operation).
    • Disadvantages:
      • Radioactive Waste: Spent fuel and byproducts are highly radioactive and hazardous for thousands of years; safe disposal is a major challenge.
      • Risk of Accidents: Accidents (like Chernobyl, Fukushima) can release large amounts of radiation with catastrophic environmental and health consequences.
      • High Costs: Building and decommissioning nuclear plants are extremely expensive.
      • Non-renewable Fuel: Uranium reserves are finite.
      • Security Concerns: Risk of nuclear materials proliferation.
    • Nuclear Fusion:
      • Process: Fusing of two light nuclei (like isotopes of hydrogen - deuterium and tritium) to form a heavier nucleus (like helium) at extremely high temperatures (~10^7 K) and pressures. Releases even more energy than fission per unit mass.
      • Source of Stellar Energy: This is how the Sun and stars produce energy.
      • Challenges: Achieving and containing the required high temperatures and pressures for sustained fusion on Earth is extremely difficult (requires magnetic confinement or inertial confinement).
      • Potential Advantages (if achieved): Abundant fuel (deuterium from water, lithium for tritium), inherently safer than fission (no long-lived radioactive waste, no meltdown risk), higher energy yield. Currently in the experimental stage (e.g., ITER project).

6. Environmental Consequences of Energy Use

  • Burning fossil fuels is the primary cause of air pollution, acid rain, and global warming.
  • Hydroelectric projects cause ecological imbalance and displacement.
  • Nuclear energy poses risks of radiation leakage and waste disposal problems.
  • Even 'clean' sources like wind and solar have environmental footprints (land use, manufacturing impacts, visual/noise pollution).
  • The choice of energy source involves trade-offs between cost, availability, efficiency, and environmental impact.
  • No source is entirely risk-free or impact-free.

7. How Long Will Energy Resources Last?

  • Non-renewable resources (fossil fuels, uranium) are finite and depleting rapidly. Estimates vary, but coal might last a couple of centuries, while oil and natural gas reserves are projected to last for several decades at current consumption rates.
  • Renewable resources are sustainable in the long term if managed properly.
  • Transitioning to renewable energy sources and improving energy efficiency are crucial for energy security and environmental protection.

8. Energy Conservation

  • "Energy saved is energy generated."
  • Reducing energy consumption through conscious choices (switching off lights/fans, using public transport, choosing energy-efficient appliances - BEE star ratings) is essential.
  • Improving efficiency in energy generation, transmission, and usage minimizes waste.

Conclusion:
Our energy demands are increasing. While conventional sources have powered our development, their environmental impact and finite nature necessitate a shift towards cleaner, sustainable, non-conventional, and renewable energy sources. Energy conservation and efficiency are equally vital components of a sustainable energy future.

Multiple Choice Questions (MCQs)

  1. Which of the following is a non-renewable source of energy?
    (a) Wood
    (b) Sun
    (c) Fossil fuels
    (d) Wind

  2. Acid rain happens because:
    (a) Sun leads to heating of the upper layer of the atmosphere.

    • (b) Burning of fossil fuels releases oxides of carbon, nitrogen, and sulphur in the atmosphere.
      (c) Nuclear power plants release radiation into the atmosphere.
      (d) Earth’s atmosphere contains acids.

  3. Fuel used in thermal power plants is primarily:
    (a) Water
    (b) Uranium
    (c) Biomass
    (d) Fossil Fuels (like Coal)

  4. In a hydro power plant:
    (a) Potential energy possessed by stored water is converted into electricity.
    (b) Kinetic energy possessed by stored water is converted into potential energy.
    (c) Electricity is extracted from water.
    (d) Water is converted into steam to produce electricity.

  5. Which of the following is NOT a disadvantage of establishing a hydro power plant?
    (a) Displacement of people and submergence of land.
    (b) It does not cause air pollution during operation.
    (c) High setup cost and time.
    (d) Adverse effects on aquatic ecosystems.

  6. Biogas is mainly composed of:
    (a) Methane
    (b) Carbon dioxide
    (c) Hydrogen sulphide
    (d) Butane

  7. Solar cells convert solar energy directly into:
    (a) Heat energy
    (b) Mechanical energy
    (c) Electrical energy
    (d) Chemical energy

  8. The energy source that utilizes the temperature difference at different levels in the ocean is:
    (a) Tidal energy
    (b) Wave energy
    (c) Ocean Thermal Energy Conversion (OTEC)
    (d) Geothermal energy

  9. In a nuclear reactor, control rods (like cadmium rods) are used to:
    (a) Speed up the neutrons.
    (b) Slow down the neutrons.
    (c) Absorb excess neutrons and control the fission rate.
    (d) Transfer heat generated to the coolant.

  10. Which phenomenon is utilized by a box-type solar cooker to trap heat?
    (a) Reflection
    (b) Refraction
    (c) Greenhouse effect
    (d) Conduction

Answer Key:

  1. (c)
  2. (b)
  3. (d)
  4. (a)
  5. (b) (This is an advantage, not a disadvantage)
  6. (a)
  7. (c)
  8. (c)
  9. (c)
  10. (c)

Study these notes thoroughly. Understand the working principles, advantages, and limitations of each energy source. Also, keep the environmental impact in mind. This will prepare you well for questions from this chapter. Good luck!

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