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Chapter 5 - Towards Green Energy

Chapter 5 : Towards Green Energy

Textbook Exercise Solutions

Q1) Remake the table taking into account relation between entries in three columns:
Answer :

The correctly matched three columns showing fuel/source, form of energy, and corresponding power plant are:

Column I (Energy Source / Fuel) Column II (Energy Form) Column III (Power Plant)
1. Coal Thermal energy Thermal power plant
2. Uranium Nuclear energy Nuclear power plant
3. Water reservoir Potential energy Hydroelectric power plant
4. Wind Kinetic energy Wind electricity plant
Q2) Which fuel is used in thermal power plant? What are the problems associated with this type of power generation?
Answer :

1. Fuel Used: Coal is used as fuel in thermal power plants. Chemical energy stored in coal is converted into heat energy by combustion.

2. Associated Environmental and Health Problems:

  1. Air Pollution: Burning coal releases harmful greenhouse and toxic gases like carbon dioxide (CO2), carbon monoxide (CO), sulfur dioxide (SO2), and nitrogen oxides (NOx).
  2. Global Warming: Excessive CO2 emission directly fuels the greenhouse effect, raising global temperatures and melting polar ice caps.
  3. Acid Rain: Oxides of sulfur and nitrogen combine with rainwater to form acid rain, which damages crops, soil fertility, and aquatic life.
  4. Health Hazards: Fine soot and fly ash particles suspended in the air enter human lungs, triggering chronic respiratory illnesses like asthma, bronchitis, and lung disorders.
  5. Depletion of Reserves: Coal is a non-renewable fossil fuel; over-mining is exhausting domestic coal reserves rapidly.
Q3) Other than thermal power plant, which power plants use thermal energy for power generation? In what different ways is the thermal energy obtained?
Answer :

Power plants other than coal-based plants that utilize thermal energy to generate electricity are:

  1. Nuclear Power Plants: Thermal energy is released through the nuclear fission of radioactive heavy nuclei such as Uranium-235 or Plutonium-239. The massive heat turns water into high-pressure steam to rotate turbines.
  2. Natural Gas Power Plants: Natural gas is burned in a combustion chamber under high pressure, producing superheated expanding gases that directly spin the gas turbine.
  3. Solar Thermal Power Plants: Parabolic solar concentrators and mirrors reflect and concentrate solar radiation onto heat absorbers to heat water or synthetic oil, generating steam to rotate steam turbines.
  4. Geothermal Power Plants: Underground geothermal steam and superheated water trapped inside volcanic geological strata are tapped directly to rotate turbines.
Q4) Which type/types of power generation involve maximum number of steps of energy conversion? In which power generation is the number minimum?
Answer :
  1. Maximum Steps of Energy Conversion: Thermal Power Generation involves the maximum number of steps (5 steps):
    Chemical energy in coal → Thermal energy → Kinetic energy in steam → Kinetic energy in turbine → Electrical energy.
  2. Minimum Steps of Energy Conversion:
    • Solar Photovoltaic (PV) Generation has the minimum number of steps (just 1 single direct step): Solar radiant light energy → Electrical energy directly via photovoltaic effect.
    • Among turbine-based systems, Wind Power Generation involves the fewest steps (3 steps): Kinetic energy in wind → Kinetic energy in turbine → Electrical energy.
Q5) Fill in the blanks:
1. Maximum energy generation in India is done using ............... energy.
Answer :

Maximum energy generation in India is done using thermal energy (coal-based).

2. .......... energy is a renewable source of energy.
Answer :

Wind (or Solar / Hydroelectric) energy is a renewable source of energy.

3. Solar energy can be called ....... energy.
Answer :

Solar energy can be called green (or clean / eco-friendly) energy.

4. ....... energy of wind is used in wind mills.
Answer :

Kinetic energy of wind is used in wind mills.

5. .......... energy of water in dams is used for generation of electricity.
Answer :

Potential energy of water in dams is used for generation of electricity.

Q6) Explain the difference:
1. Conventional and Non-conventional Sources of Energy:
Answer :
Point of Distinction Conventional Energy Sources Non-Conventional Energy Sources
Availability & Nature Exhaustible and non-renewable; reserves are limited. Inexhaustible and renewable; available in abundance.
Environmental Impact Highly polluting; emits greenhouse gases and soot. Clean and eco-friendly; zero toxic emissions.
Examples Coal, petroleum, natural gas, uranium. Solar energy, wind energy, tidal energy, biomass.
2. Thermal Electricity Generation and Solar Thermal Electricity Generation:
Answer :
Point of Distinction Thermal Electricity Generation Solar Thermal Electricity Generation
Primary Heat Source Burning coal in boilers releases thermal energy. Concentrated solar radiation reflected by mirrors heats water.
Pollution Emits smoke, CO2, SO2, and ash. Completely clean; produces no smoke or pollutants.
Fuel Availability Depends on exhaustible fossil coal reserves. Depends on inexhaustible, free sunlight.
Q7) What is meant by green energy? Which energy sources can be called green energy sources and why? Give examples:
Answer :

1. Meaning of Green Energy:

Energy generated from natural, renewable, and inexhaustible resources that does not produce toxic fumes, greenhouse gases, or radioactive waste and causes no harm to the environment is called Green Energy.

2. Why They Are Called Green Energy Sources:

  1. They produce electricity without burning polluting fossil fuels.
  2. They do not release harmful carbon emissions, soot, or toxic residues.
  3. They are perpetually replenished by natural planetary cycles and will never get exhausted.

3. Examples of Green Energy:

  • Solar Energy: Generated using photovoltaic cells or solar thermal concentrators.
  • Wind Energy: Harnessing kinetic energy of atmospheric winds via wind turbines.
  • Hydroelectric Energy: Generated by potential energy of falling stored water.
  • Biomass & Biofuels: Energy derived from organic agricultural waste and biogas.
  • Ocean & Tidal Energy: Generated by gravitational tidal surges of seawater.
Q8) Explain the following sentences:
1. Energy obtained from fossil fuels is not green energy:
Answer :
  1. Fossil fuels (coal, crude oil, natural gas) consist of hydrocarbons formed over millions of years inside the Earth's crust.
  2. Combustion of fossil fuels releases tons of greenhouse gases like carbon dioxide and toxic gases like carbon monoxide, sulfur dioxide, and nitrogen oxides into the air.
  3. This causes global warming, acid rain, smog, and severe respiratory diseases.
  4. Additionally, fossil fuels are non-renewable and rapidly getting depleted.
  5. Because they degrade the environment and cause severe pollution, energy from fossil fuels can never be considered green energy.
2. Saving energy is the need of the hour:
Answer :
  1. Modern lifestyle, industrial machinery, and digital technology rely continuously on electric power.
  2. Over 60% of India's electricity is still produced by burning limited reserves of coal in thermal plants.
  3. Excessive consumption accelerates fossil fuel depletion and multiplies atmospheric carbon emissions, worsening global climate disasters.
  4. Renewable green energy infrastructure takes substantial time, capital, and technology to fully replace fossil power plants.
  5. Every unit of electricity saved directly avoids burning coal and cutting trees. Hence, "Electricity saved is electricity generated", making energy conservation the urgent need of the hour.
Q9) Answer the following questions:
1. How can we get the required amount of energy by connecting solar panels?
Answer :
  1. A single silicon solar cell generates a small potential difference of about 0.5 V and current of 30 mA/cm2.
  2. Series Combination: When solar cells are connected in series, their voltages add up, while current remains constant (V = V1 + V2, I = constant).
  3. Parallel Combination: When solar cells are connected in parallel, their currents add up, while potential difference remains constant (I = I1 + I2, V = constant).
  4. By connecting many solar cells in series and parallel, a solar panel is manufactured.
  5. Several solar panels connected in series form a solar string, and many strings connected in parallel form a solar array.
  6. In this way, any desired voltage and current output—from milliwatts (mW) for pocket calculators to megawatts (MW) for power stations—can be generated.
2. What are the advantages and limitations of solar energy?
Answer :

A. Advantages:

  • No fuel is combusted; hence, zero air, water, or soil pollution.
  • Sunlight is free, abundant, inexhaustible, and available everywhere.
  • Rooftop solar panels enable decentralized home electricity generation with low maintenance.

B. Limitations:

  • Sunlight is available only during clear daytime; power generation drops on cloudy, foggy, or rainy days.
  • Solar cells generate Direct Current (DC), requiring costly inverters to convert DC into Alternating Current (AC) for household appliances.
  • Large battery storage systems are required to store electricity for nighttime use.
Q10) Explain with diagram step-by-step energy conversion in:
1. Thermal Power Plant:
Answer :
Chemical energy in coal → Thermal energy → Kinetic energy in steam → Kinetic energy in turbine → Electrical energy
2. Nuclear Power Plant:
Answer :
Nuclear energy → Thermal energy → Kinetic energy in steam → Kinetic energy in turbine → Electrical energy
3. Solar Thermal Power Plant:
Answer :
Thermal energy from solar radiation → Kinetic energy in steam → Kinetic energy in turbine → Electrical energy
4. Hydroelectric Power Plant:
Answer :
Potential energy in dam reservoir → Kinetic energy in flowing water → Kinetic energy in turbine → Electrical energy
Q11) Give scientific reasons:
1. The construction of turbine is different for different types of power plants:
Answer :
  1. In any electric generator, mechanical rotation of the armature inside a magnetic field generates electricity via electromagnetic induction.
  2. The driving fluid that strikes the turbine blades differs across power plants: steam at extreme temperature and pressure is used in thermal/nuclear plants; high-density flowing water under gravity is used in hydroelectric plants; and ambient atmospheric air is used in wind turbines.
  3. Because the density, velocity, and thermodynamic state of each driving fluid are completely different, the blade curvature, material, size, and mechanical construction of each turbine must be specifically engineered to maximize conversion efficiency.
2. It is absolutely necessary to control the fission reaction in nuclear power plants:
Answer :
  1. Nuclear fission of Uranium-235 is a self-sustaining chain reaction. One slow neutron striking a U-235 nucleus splits it into Barium and Krypton, releasing an immense amount of energy and 3 new fast neutrons.
  2. Each of these 3 neutrons can split 3 more uranium atoms, releasing 9 neutrons, then 27, and so on in geometric progression.
  3. If not carefully controlled using neutron-absorbing control rods (such as cadmium or boron rods) and moderators, this uncontrolled exponential chain reaction can cause catastrophic core meltdown and massive nuclear explosions.
3. Hydroelectric energy, solar energy and wind energy are called renewable energies:
Answer :
  1. Unlike coal and crude oil, which take millions of years to form and will eventually be exhausted, sunlight, wind, and the water cycle are natural, continuous planetary processes.
  2. Sunlight shines every day, winds blow due to solar heating, and dam reservoirs are replenished every monsoon by the hydrological cycle.
  3. Since these sources are inexhaustible and naturally restored, they are called renewable energies.
4. It is possible to produce energy from mW to MW using solar photovoltaic cells:
Answer :
  1. A tiny individual solar cell produces a small voltage of ~0.5 V, which can power small devices in the milliwatt (mW) range (e.g., wristwatches, pocket calculators).
  2. By connecting multiple cells in series, the output voltage is scaled up; by connecting them in parallel, current capacity is magnified.
  3. Grouping panels into strings and assembling thousands of strings into large commercial solar arrays allows solar power parks to feed hundreds of megawatts (MW) into national electric grids.
Q12) Draw a Schematic diagram of Solar thermal electric energy generation:
Answer :
Concentrators (Solar Reflectors) Heat Absorber (Steam generation) Steam Turbine (Rotates by steam) Generator (EM Induction) Electrical Energy Condenser & Cooling Tower
Q13) Give your opinion about whether hydroelectric plants are environment-friendly or not?
Answer :

Hydroelectric energy has notable advantages as a renewable power source, but it also carries significant ecological and human costs:

1. Environment-friendly Aspects:

  • No fuel combustion is needed; it generates no smoke, CO2, or air pollutants.
  • Water is continuously replenished by the annual monsoon cycle.
  • Reservoirs provide water for agricultural irrigation and control downstream river flooding.

2. Adverse Environmental & Social Impacts:

  • Building huge dams submerges vast expanses of fertile agricultural land and ancient forest biodiversity.
  • Submerged vegetation decays anaerobically under water, releasing methane (a potent greenhouse gas).
  • Thousands of indigenous villagers and farmers are displaced from their ancestral homes, facing severe socio-economic hardships.
  • Natural migration and breeding of aquatic river fauna (fishes) are obstructed.

Conclusion: While hydroelectricity is clean in operational terms, its construction causes major ecological disruptions. Hence, small micro-hydel projects are far more eco-friendly than mega dams.

Q14) Draw neat labelled diagrams:
1. Energy transformation in solar thermal electric energy generation:
Answer :

Solar Radiant Energy → Thermal Energy in Absorber → Kinetic Energy in Steam → Mechanical Energy in Turbine → Electrical Energy

2. Numerical on Solar Array Design:
One solar panel produces a potential difference of 18 V and current of 3 A. Describe how you can obtain a potential difference of 72 Volts and current of 9 A with a solar array using solar panels.
Answer :

Given:

  • Potential difference of 1 panel (V1) = 18 V
  • Current of 1 panel (I1) = 3 A
  • Target voltage = 72 V
  • Target current = 9 A

Design Calculation:

  1. To increase voltage, panels must be connected in series:
    Number of panels in series = 72 V ÷ 18 V = 4 panels in each series string.
    This string produces 72 V and 3 A.
  2. To increase current from 3 A to 9 A, strings must be connected in parallel:
    Number of parallel strings = 9 A ÷ 3 A = 3 strings in parallel.
  3. Total number of solar panels required:
    4 (panels per string) × 3 (parallel strings) = 12 solar panels.

Arrangement: Connect 4 solar panels in series to form a string (72 V, 3 A). Connect 3 such identical strings in parallel to obtain the required 72 V and 9 A solar array output.

Q15) Write a short note on Electrical energy generation and environment:
Answer :
  1. Electricity generation is vital for global economic, industrial, and social development, but conventional generation methods inflict severe damage on the biosphere.
  2. Thermal Power Generation: Burning coal produces toxic emissions (CO, SO2, NOx) and millions of tons of fly ash, causing greenhouse warming and respiratory illnesses.
  3. Nuclear Power: Though it produces zero carbon emissions, managing spent radioactive nuclear waste and the risk of nuclear accidents (like Chernobyl and Fukushima) pose grave ecological threats.
  4. Fossil Fuel Depletion: Coal and crude oil deposits are rapidly depleting and will be exhausted within a few decades.
  5. The Green Alternative: Humanity must rapidly transition toward non-polluting green energy sources such as solar photovoltaic, wind energy, small hydro power, and biofuels to ensure environmental sustainability and protect the future of Earth.
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Chapter Overview: Towards Green Energy

Class 10 Science 2 Chapter 5 explores electricity generation based on electromagnetic induction, thermal power plants, nuclear fission, natural gas plants, hydroelectric power, wind mills, solar thermal electric generation, photovoltaic solar cells, series and parallel array combinations, environmental impacts, and green energy alternatives.

Frequently Asked Questions (FAQs)

Q1. Why are solar energy and wind energy called green energies?

Because they do not burn fossil fuels, emit zero carbon dioxide or toxic gases, produce no ash, and rely on infinite renewable natural cycles.

Q2. How is nuclear energy controlled in a reactor?

Boron or cadmium control rods absorb excess neutrons to maintain a steady, controlled fission chain reaction, preventing runaway core meltdowns.

Q3. What is the difference between connecting solar cells in series vs parallel?

Connecting solar cells in series adds voltages together (increasing total voltage), while connecting them in parallel adds currents together (increasing total current).

Related Study Topics

Class 10 Science 2 Chapter 5 Thermal Power Plant Conversion Nuclear Power Chain Reaction Hydroelectric Power Advantages Solar Photovoltaic Cell Array Green Energy Examples Solar Panel Numericals
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