🌍 The Energy Crisis: Why Does It Exist?

We know energy is conserved, yet we face an energy crisis. Why? While energy changes form, much of it gets dissipated in less usable ways. For example, burning a candle converts chemical energy into heat and light, but we can’t recover the wax. Similarly, once hot water cools, its lost heat can’t be reused.

The problem isn’t losing energy—it’s losing usable energy. Non-renewable sources deplete quickly, making sustainability crucial. Let’s explore how we can use energy efficiently and rely more on renewable sources. ⚡🌱

14.1 WHAT IS A GOOD SOURCE OF ENERGY?

Introduction

Energy is essential for performing daily activities, from cooking food to running machines. The choice of an energy source depends on various factors like availability, efficiency, and cost-effectiveness. A good source of energy should provide maximum work while being easily accessible and economical.

Forms of Energy in Daily Life

We use different forms of energy from morning till we reach school. Some examples include:

Muscular Energy – Used for walking, cycling, or lifting objects.
Electrical Energy – Used in household appliances, lighting, and gadgets.
Chemical Energy – Present in food for body metabolism and in fuels like petrol and LPG.
Solar Energy – Used for heating water, drying clothes, and generating electricity in solar panels.

Each form of energy comes from a specific source, such as food, fuel, the sun, or power plants.

Characteristics of a Good Source of Energy

A good source of energy should have the following properties:

High Energy Output – It should produce a large amount of energy per unit mass or volume.
Easy Availability – The source should be easily accessible to people.
Minimal Pollution – It should produce little or no harmful by-products like smoke or greenhouse gases.
Ease of Storage and Transport – It should be easy to store and transport without significant loss or risk.
Cost-Effective – The energy source should be affordable and economical for widespread use.

Factors Affecting Choice of Energy Source

The choice of energy depends on location, availability, and purpose. For example:

Forest areas – Wood or biomass might be the primary fuel.
Remote mountain villages or islands – Limited access to fuels like LPG, reliance on local sources like firewood.
Urban areas (e.g., New Delhi) – Dependence on electricity, LPG, and natural gas due to infrastructure availability.
Five centuries ago – Only natural sources like wood, animal energy, and wind power were available.

Different fuels are used for different purposes: LPG for cooking, coal for industries, and electricity for lighting.

Questions to Consider When Choosing a Fuel

Apart from the three given criteria (heat output, smoke production, and availability), other important factors include:

Renewability – Is the energy source renewable or non-renewable?
Safety – Does the fuel pose risks like explosion, leakage, or toxicity?
Efficiency – How much energy is lost as waste during use?

Conclusion

A good energy source must be efficient, available, environmentally friendly, and affordable. As energy demand increases, we must focus on sustainable energy sources like solar, wind, and hydroelectric power to ensure a stable future. 🚀♻️

Q U E S T I O N S & A N S W E R S

1. What is a good source of energy?

✅ Answer:
A good source of energy is one that:

Produces a large amount of energy per unit mass or volume.
Is easily available and accessible.
Does not cause pollution or harm the environment.
Is easy to store and transport.
Is economical and cost-effective.

2. What is a good fuel?

✅ Answer:
A good fuel should have the following properties:

High calorific value (provides a lot of energy per unit mass).
Burns efficiently with minimal wastage.
Produces little or no pollution (low emissions of smoke and harmful gases).
Easily available and affordable.
Safe to store and transport without risk of explosion or leakage.

3. If you could use any source of energy for heating your food, which one would you use and why?

✅ Answer:
I would use LPG (Liquefied Petroleum Gas) for heating food because:

It has a high calorific value, providing efficient heat.
It burns cleanly, producing minimal smoke or pollutants.
It is easily available and convenient to use.
It allows precise temperature control for cooking.

Alternatively, in an eco-friendly setting, I could use solar energy (solar cookers) as it is renewable, free, and environmentally friendly. However, it depends on weather conditions and may not be available at night or on cloudy days. 🌞🔥

14.2 CONVENTIONAL SOURCES OF ENERGY

Introduction

Conventional sources of energy are those that have been traditionally used for centuries. These include fossil fuels, hydro power, bio-mass, and wind energy. While they have powered industrialization and economic growth, their excessive use has led to environmental issues such as pollution and depletion of resources.

14.2.1 Fossil Fuels

Fossil fuels like coal, petroleum, and natural gas are non-renewable sources of energy that were formed over millions of years from the remains of plants and animals.

Importance of Fossil Fuels

They played a crucial role in the industrial revolution.
They are widely used for electricity generation, transportation, and heating.
Technologies are developed for their efficient utilization.

Disadvantages of Fossil Fuels

Non-renewable – Once used, they cannot be replenished quickly.
Causes Pollution – Burning fossil fuels releases carbon dioxide, nitrogen oxides, and sulfur oxides, leading to:
- Acid rain, which harms soil and water.
- Greenhouse effect, which contributes to global warming.
Health Hazards – Air pollution causes respiratory diseases.
Limited Reserves – The rapid consumption of fossil fuels could lead to an energy crisis in the future.

How to Reduce Fossil Fuel Pollution?

Improve efficiency of combustion processes.
Use pollution control technologies to filter harmful gases.
Shift to alternative energy sources to reduce dependence.

14.2.2 Thermal Power Plants

Definition: A power plant where fossil fuels (coal, petroleum, or natural gas) are burned to heat water, producing steam that drives a turbine to generate electricity.
Efficiency: More efficient than transporting fossil fuels over long distances.
Location: Usually built near coal or oil fields to reduce transportation costs.

Disadvantages:

Requires large amounts of fossil fuels.
Causes pollution (smoke, ash, and greenhouse gases).
High water consumption for cooling.

14.2.3 Hydro Power Plants

Definition: Converts the potential energy of stored water in dams into kinetic energy, which then turns a turbine to generate electricity.
Renewable Source: Water from rainfall refills reservoirs, making it sustainable.

Advantages of Hydro Power Plants

✔️ Renewable – Water cycle naturally replenishes resources.
✔️ No pollution – No harmful emissions.
✔️ High efficiency – Direct conversion of water’s potential energy into electricity.

Disadvantages of Hydro Power Plants

❌ Limited Locations – Dams can only be built in suitable terrains (hilly regions).
❌ Displacement of people – Large areas of human settlements and agricultural land get submerged.
❌ Environmental Impact – Destroys ecosystems and leads to methane emissions from decaying vegetation underwater.
❌ High Initial Cost – Requires huge investment and long construction time.

Examples of Hydro Power Projects in India

Tehri Dam (Ganga River) – Uttarakhand
Sardar Sarovar Dam (Narmada River) – Gujarat
Bhakra Nangal Dam (Sutlej River) – Himachal Pradesh

14.2.4 Improvements in Technology for Conventional Sources of Energy

Bio-Mass

Bio-mass includes wood, cow-dung cakes, crop residue, and organic waste. It is a renewable source of energy but requires improvement in efficiency.

Bio-Mass Fuel Types

Charcoal
- Produced by burning wood in limited oxygen.
- Burns with no smoke and has high heat efficiency.
Bio-Gas (Gobar Gas)
- Produced by anaerobic decomposition of organic matter.
- Contains methane (75%), making it a clean and efficient fuel.
- Used for cooking, lighting, and electricity generation.
- Eco-friendly – Provides waste management and produces organic manure.

Advantages of Bio-Gas

✔️ Smokeless burning – No indoor pollution.
✔️ High heating capacity – Better than wood and dung cakes.
✔️ Manure production – Provides organic fertilizer.
✔️ Safe waste disposal – Converts waste into useful energy.

14.2.5 Wind Energy

Wind energy is harnessed from the kinetic energy of moving air to generate electricity using windmills.

Working of Windmills

Wind rotates large blades attached to a turbine.
The turbine spins and drives a generator to produce electricity.
Wind farms (groups of windmills) are set up for large-scale production.

Advantages of Wind Energy

✔️ Renewable and eco-friendly – No air pollution or greenhouse gas emissions.
✔️ No fuel cost – Uses natural wind power.
✔️ Low operating cost – After installation, maintenance is minimal.

Limitations of Wind Energy

❌ Dependent on Wind Speed – Needs consistent wind flow above 15 km/h.
❌ Large Land Requirement – A 1 MW wind turbine needs about 2 hectares of land.
❌ High Initial Cost – Expensive to set up and maintain.
❌ Unreliable Supply – Needs backup storage for windless days.

Wind Energy in India

India ranks 5th in wind energy production.
The largest wind farm is located in Kanyakumari, Tamil Nadu, generating 380 MW.
Potential wind energy in India: 45,000 MW if fully harnessed.

Conclusion

Conventional sources of energy have been essential for development but come with drawbacks like pollution, resource depletion, and high costs. While fossil fuels are non-renewable, hydro power, biomass, and wind energy offer renewable alternatives. Moving towards sustainable energy solutions is crucial for a cleaner and more energy-efficient future. 🌱⚡

Q U E S T I O N S & A N S W E R S

1. What are the disadvantages of fossil fuels?

✅ Answer:
Fossil fuels (coal, petroleum, and natural gas) have several disadvantages:

Non-Renewable – They take millions of years to form and are depleting rapidly.
Air Pollution – Burning fossil fuels releases carbon dioxide, nitrogen oxides, and sulfur oxides, leading to:
- Acid rain that damages soil and water.
- Greenhouse effect causing global warming.
Health Hazards – Causes respiratory problems and other diseases.
Limited Reserves – Rapid consumption could lead to an energy crisis.
Environmental Damage – Mining and oil drilling harm ecosystems.

2. Why are we looking at alternate sources of energy?

✅ Answer:
We need alternative sources of energy because:

Fossil fuels are depleting – They are non-renewable and won’t last forever.
Pollution control – Renewable sources like solar and wind energy are cleaner and do not contribute to global warming.
Energy security – Reducing dependence on imported fuels ensures a stable energy supply.
Sustainable development – Renewable energy sources help in long-term environmental conservation.
Cost-effectiveness – Once set up, renewable energy sources require low operational costs.

3. How has the traditional use of wind and water energy been modified for our convenience?

✅ Answer:
Traditional use of wind and water energy has been improved using modern technology:

Wind Energy:
- Earlier: Used in windmills for grinding grains and pumping water.
- Now: Used in wind turbines to generate electricity on a large scale.
- Example: Wind energy farms in Tamil Nadu generate 380 MW of power.
Water Energy (Hydro Power):
- Earlier: Used directly in water wheels for mechanical work.
- Now: Hydro power plants store water in dams and use its potential energy to generate electricity efficiently.
- Example: Tehri Dam (Uttarakhand) and Sardar Sarovar Dam (Gujarat) generate hydroelectric power.

Modern technology has increased efficiency, reliability, and large-scale utilization of these natural energy sources. 🚀⚡

14.3 ALTERNATIVE OR NON-CONVENTIONAL SOURCES OF ENERGY

Introduction

As technology advances and energy demands rise, reliance on non-renewable sources like fossil fuels is becoming unsustainable. Alternative or non-conventional energy sources are being explored to meet energy needs while reducing pollution and resource depletion. These sources include solar energy, tidal energy, ocean thermal energy, geothermal energy, and nuclear energy.

14.3.1 Solar Energy ☀️

The Sun is an inexhaustible source of energy, radiating vast amounts of heat and light. India receives abundant solar energy (≈5,000 trillion kWh/year), making it a potential energy source for the future.

Ways to Harness Solar Energy

Solar Cookers & Water Heaters – Use black surfaces to absorb heat efficiently.
Solar Cells (Photovoltaic Cells) – Convert sunlight into electricity.
- Each cell generates 0.5-1V and 0.7W of power.
- Solar panels are used in remote areas, satellites, traffic signals, and calculators.
- Advantages: No moving parts, minimal maintenance, and works in isolated locations.
- Limitations: High cost, low efficiency, and dependence on sunlight.

14.3.2 Energy from the Sea 🌊

Tidal Energy

Generated due to the gravitational pull of the moon causing high and low tides.
A dam is built across a sea inlet to trap tidal water and release it to run turbines.
Limitations: Few suitable locations for dam construction.

Wave Energy

Uses kinetic energy of sea waves to drive turbines.
Works best where waves are strong (e.g., coastal regions with frequent storms).
Limitations: Technology still under development, and energy generation is inconsistent.

Ocean Thermal Energy (OTE)

Exploits temperature difference between warm surface water and cold deep-sea water.
Process:
1. Warm water boils a volatile liquid (e.g., ammonia).
2. Vapors run a turbine to generate electricity.
3. Cold deep water condenses the vapor to restart the cycle.
Limitation: Requires a minimum 20°C temperature difference, limiting practical locations.

14.3.3 Geothermal Energy 🌋

Generated from Earth's interior heat due to molten rocks trapped in certain regions (hot spots).
How it works?
- Underground water comes in contact with hot spots and turns into steam.
- Steam is used to rotate turbines and generate electricity.
- Natural hot water outlets are called hot springs.
Advantages:
✔️ Renewable and eco-friendly.
✔️ No fuel cost.
Limitations:
❌ Limited viable locations.
❌ High setup costs.
Examples: Used in New Zealand and the USA for power generation.

14.3.4 Nuclear Energy ☢️

Generated through nuclear fission – the splitting of a heavy atom (uranium/plutonium/thorium) by neutron bombardment, releasing enormous energy.

Nuclear Fission Process

Controlled chain reactions in a nuclear reactor release energy slowly to generate electricity.
Example reaction:
$E = Δm \cdot c^2$ (Einstein’s equation: mass-energy equivalence)
- 1 atomic mass unit (u) = 931 MeV of energy.

Advantages of Nuclear Energy

✔️ High energy yield – 1 uranium atom releases 10 million times more energy than 1 carbon atom.
✔️ Low air pollution – No greenhouse gases like fossil fuels.

Disadvantages of Nuclear Energy

❌ Nuclear waste disposal – Radioactive waste remains hazardous for centuries.
❌ Risk of radiation leaks – Can cause severe environmental and health damage.
❌ Expensive setup – High construction and maintenance costs.

Nuclear Power Plants in India

Tarapur (Maharashtra)
Kalpakkam (Tamil Nadu)
Rana Pratap Sagar (Rajasthan)
Narora (Uttar Pradesh)
Kakrapar (Gujarat)
Kaiga (Karnataka)

Despite high costs, some countries generate over 30% of their electricity from nuclear power.

14.3.5 Nuclear Fusion (Future Energy Source) ⚛️

Nuclear fusion: The joining of light atomic nuclei (e.g., hydrogen isotopes) into a heavier nucleus (e.g., helium), releasing energy.
Example Reaction:
$2H + 2H → 3He + n + Energy$
Fusion powers the Sun and stars but requires extremely high temperature (~10 million K) and pressure.
Fusion Bombs (Hydrogen Bombs) use fission explosions to create the extreme conditions needed for fusion.
Advantages over fission:
✔️ More energy than fission.
✔️ No radioactive waste.
❌ Current challenge: Achieving the conditions required for controlled fusion reactions.

Comparison of Alternative Energy Sources

Energy Source	Advantages	Limitations
Solar Energy ☀️	Renewable, no pollution, low maintenance	High setup cost, low efficiency
Tidal Energy 🌊	Predictable, no pollution	Few suitable locations
Wave Energy 🌊	Huge energy potential	Requires strong waves, expensive setup
Ocean Thermal Energy 🌊	Unlimited resource	Needs 20°C temperature difference, expensive
Geothermal Energy 🌋	Continuous power supply	Limited locations, expensive
Nuclear Energy ☢️	High energy output, no carbon emissions	Radioactive waste, risk of accidents
Nuclear Fusion ⚛️	Clean, abundant energy	Extremely high temperature and pressure required (not yet practical)

Conclusion

Alternative energy sources are essential for a sustainable future, reducing dependence on fossil fuels and minimizing environmental impact. However, many of these technologies require advancements to become commercially viable. Investing in research and innovation will help improve efficiency and reduce costs, making renewable energy the primary source for future generations. 🌍⚡♻️

Q U E S T I O N S & A N S W E R S

1. What kind of mirror – concave, convex or plane – would be best suited for use in a solar cooker? Why?

✅ Answer:
A concave mirror is best suited for a solar cooker because:

It converges sunlight to a single focal point, increasing heat concentration.
This focused heat raises the temperature effectively for cooking food.
Plane mirrors only reflect light without focusing it, and convex mirrors spread light, making them inefficient for heating.

2. What are the limitations of the energy that can be obtained from the oceans?

✅ Answer:
Energy from the oceans has the following limitations:

Limited Suitable Locations – Tidal and wave energy require specific coastal areas.
High Initial Cost – Setting up power plants is expensive.
Intermittent Availability – Tides, waves, and ocean temperature differences vary, leading to unreliable energy production.
Environmental Impact – Dams for tidal energy affect marine ecosystems and fisheries.
Low Efficiency – The energy harnessed is often less than expected due to practical limitations.

3. What is geothermal energy?

✅ Answer:
Geothermal energy is the heat energy stored deep inside the Earth, generated due to radioactive decay and magma movement.

Hot spots in the Earth’s crust heat underground water, producing steam.
This steam is used to rotate turbines and generate electricity.
Natural hot water outlets are called hot springs.

Examples:

Geothermal power plants in USA and New Zealand.
Puga Valley (Ladakh, India) has geothermal potential.

4. What are the advantages of nuclear energy?

✅ Answer:
Nuclear energy has several advantages:

High Energy Output – 1 uranium atom releases 10 million times more energy than a carbon atom.
No Greenhouse Gas Emissions – Unlike fossil fuels, it does not release CO₂.
Efficient Power Generation – Small amounts of fuel produce large amounts of electricity.
Reliable Energy Supply – Not dependent on weather conditions like solar or wind energy.
Reduces Dependence on Fossil Fuels – Helps in energy security.

However, radioactive waste disposal and nuclear accidents are major concerns. 🚀⚛️

14.4 ENVIRONMENTAL CONSEQUENCES

Introduction

Every source of energy, whether conventional or non-conventional, impacts the environment in some way. The choice of an energy source depends on:

Ease of extraction – How easily can we obtain it?
Economic feasibility – Is it affordable for large-scale use?
Technology efficiency – Can available technology harness it effectively?
Environmental impact – How much damage does it cause?

While clean energy sources like solar and wind are considered environmentally friendly, even their production and installation can affect the ecosystem.

Environmental Impact of Different Energy Sources

Energy Source	Environmental Impact
Fossil Fuels (Coal, Oil, Gas)	Causes air pollution, acid rain, and greenhouse gas emissions, leading to global warming. Mining and drilling destroy ecosystems.
Thermal Power Plants	Uses large amounts of coal or oil, releasing carbon dioxide (CO₂), sulfur oxides (SOx), and nitrogen oxides (NOx), causing acid rain.
Hydro Power (Dams)	Submerges forests, villages, and ecosystems. Produces methane from decaying vegetation. Displaces people.
Nuclear Energy	Produces radioactive waste that remains dangerous for centuries. Risk of nuclear accidents (e.g., Chernobyl, Fukushima).
Solar Energy	No pollution in operation, but manufacturing solar panels requires mining silicon and metals, causing waste.
Wind Energy	No emissions, but wind turbines require large land areas and affect bird migration.
Geothermal Energy	Releases toxic gases like hydrogen sulfide (H₂S) and can disturb underground ecosystems.
Tidal & Wave Energy	Affects marine life and changes coastal ecosystems.
Bio-Mass & Bio-Gas	Burning emits CO₂ and particulate matter, though cleaner than fossil fuels.

Key Environmental Concerns

1️⃣ Air Pollution

Fossil fuels release CO₂, SOx, and NOx, leading to smog, acid rain, and respiratory diseases.
Burning biomass also contributes to air pollution.

2️⃣ Climate Change & Global Warming

Greenhouse gases (CO₂, CH₄) from fossil fuels trap heat, raising Earth’s temperature.
Melting glaciers, rising sea levels, and extreme weather are consequences.

3️⃣ Land Degradation & Deforestation

Coal mining and oil drilling damage land and forests.
Dams submerge large land areas, affecting biodiversity.

4️⃣ Water Pollution & Scarcity

Oil spills damage marine life.
Thermal power plants require large amounts of water, reducing availability for agriculture.

5️⃣ Radioactive Waste

Nuclear plants produce dangerous waste that must be stored securely for thousands of years.

Finding the Best Energy Source 🔎

No source is completely pollution-free, but we should aim for sustainable energy with minimal impact.

✔️ Best Choices: Solar, Wind, Hydro, and Bio-Gas – Renewable and cleaner than fossil fuels.
✔️ Worst Choices: Coal, Oil, and Nuclear (due to waste management issues).
✔️ Improvement Needed: Better technology to reduce environmental harm from all energy sources.

Conclusion

To reduce environmental damage, we must:

Shift to renewable energy sources.
Improve efficiency in energy use.
Develop cleaner technologies for energy production.

🌍 Sustainable energy = A cleaner and healthier future! ♻️💡

Q U E S T I O N S & A N S W E R S

1. Can any source of energy be pollution-free? Why or why not?

✅ Answer:
No, no energy source is completely pollution-free. Even the cleanest energy sources have some environmental impact:

Solar Energy – Manufacturing solar panels requires mining silicon and metals, leading to waste.
Wind Energy – Wind turbines affect bird migration and require large land areas.
Hydro Power – Dams submerge forests and villages, affecting ecosystems.
Fossil Fuels & Nuclear – Cause air pollution, greenhouse gas emissions, and radioactive waste.

Conclusion: While some sources are cleaner than others, every energy source has some impact during manufacturing, installation, or disposal.

2. Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not?

✅ Answer:
Yes, hydrogen is a cleaner fuel than CNG (Compressed Natural Gas) because:
✔️ Hydrogen burns completely to produce only water vapor (H₂O), while CNG releases CO₂ (a greenhouse gas).
✔️ No harmful emissions – Unlike CNG, hydrogen does not emit carbon monoxide (CO) or nitrogen oxides (NOx).
✔️ High energy efficiency – Hydrogen has a higher energy content per unit mass than CNG.

However, hydrogen has challenges:
❌ Storage & transportation issues – Requires high-pressure tanks and cryogenic storage.
❌ Production energy-intensive – Most hydrogen today is produced from fossil fuels, which cause pollution.

Conclusion: Hydrogen is a cleaner fuel than CNG but needs better technology for safe and cost-effective use. 🚀♻️

14.5 HOW LONG WILL AN ENERGY SOURCE LAST US?

Introduction

Energy sources are classified based on their availability and sustainability. Some sources are limited and depleting, while others can be replenished naturally over time. Understanding these classifications helps in efficient energy management for future generations.

Types of Energy Sources

1️⃣ Exhaustible (Non-Renewable) Sources

These cannot be replaced once used and will eventually run out.

Examples:

Fossil Fuels (Coal, Petroleum, Natural Gas) – Formed over millions of years, but depleting due to excessive use.
Nuclear Fuels (Uranium, Thorium) – Limited reserves and require mining.

✅ Why should we worry?

Coal may last 200 years, but consumption is increasing rapidly, leading to faster depletion.
Fossil fuel burning causes pollution and global warming.
Nuclear waste management is a challenge.

2️⃣ Inexhaustible Sources

These will never run out and are available in abundant supply.

Examples:

Solar Energy – The Sun will last for 5 billion years, making it an unlimited energy source.
Wind Energy – Generated by atmospheric movements, never depletes.
Geothermal Energy – Heat from Earth’s core is continuously replenished.

✅ Why don’t we worry?

Sunlight, wind, and Earth's heat are naturally replenished and not affected by human use.

3️⃣ Renewable Sources

These can be replenished naturally over time if used wisely.

Examples:

Bio-Mass (Wood, Gobar Gas, Agricultural Waste) – Can be regenerated if trees are replanted and organic waste is managed properly.
Hydro Power – Water cycle replenishes rivers and reservoirs, ensuring continuous energy production.

✅ Why are they sustainable?

Proper management ensures continuous supply.
Dependence on natural cycles makes them eco-friendly.

4️⃣ Non-Renewable Sources

These cannot be replenished quickly and will eventually run out.

Examples:

Coal, Oil, and Natural Gas – Take millions of years to form but are being used up rapidly.
Nuclear Energy (Uranium & Thorium) – Limited availability and complex waste disposal.

✅ Why are they unsustainable?

Once exhausted, they cannot be replaced.
Mining and extraction damage the environment.

Conclusion

To ensure a sustainable energy future, we must:

Reduce dependence on non-renewable sources.
Invest in renewable and inexhaustible energy like solar, wind, and bio-mass.
Develop cleaner technologies to improve energy efficiency.

🌍 A shift towards renewable energy is essential for long-term energy security! ♻️⚡

Q U E S T I O N S & A N S W E R S

1. Name two energy sources that you would consider to be renewable. Give reasons for your choices.

✅ Answer:
Two renewable energy sources are:

1️⃣ Solar Energy ☀️

The Sun provides energy continuously and is expected to last for 5 billion years.
It does not deplete with use and is freely available.

2️⃣ Wind Energy 💨

Wind is generated due to uneven heating of the Earth’s surface by the Sun.
It can be harnessed repeatedly without running out.

✔️ Both sources are naturally replenished and do not cause pollution.

2. Give the names of two energy sources that you would consider to be exhaustible. Give reasons for your choices.

✅ Answer:
Two exhaustible energy sources are:

1️⃣ Coal 🏭

Formed over millions of years from decomposed plant material.
Once burned, it cannot be replaced quickly, making it non-renewable.

2️⃣ Petroleum ⛽

Created from organic matter under high pressure over millions of years.
Excessive use for fuel and chemicals is depleting reserves rapidly.

❌ Both sources take millions of years to form but are being consumed at a much faster rate.

E X E R C I S E S

1. A solar water heater cannot be used to get hot water on:

(a) a sunny day. (b) a cloudy day. (c) a hot day. (d) a windy day.

✅ Answer: (b) A cloudy day.

Solar water heaters require sunlight to function.
On cloudy days, sunlight is blocked, reducing heat absorption.

2. Which of the following is not an example of a bio-mass energy source?

(a) wood (b) gobar-gas (c) nuclear energy (d) coal

✅ Answer: (c) Nuclear energy.

Wood, gobar-gas, and crop waste are derived from organic materials (bio-mass).
Nuclear energy comes from uranium/plutonium, not plant or animal matter.

3. Most of the energy sources we use represent stored solar energy. Which of the following is not ultimately derived from the Sun’s energy?

(a) geothermal energy (b) wind energy (c) nuclear energy (d) bio-mass

✅ Answer: (a) Geothermal energy.

Wind, bio-mass, and fossil fuels are indirectly powered by the Sun.
Geothermal energy comes from heat inside the Earth, not from the Sun.

4. Compare and contrast fossil fuels and the Sun as direct sources of energy.

✅ Answer:

Feature	Fossil Fuels	Sun
Nature	Non-renewable	Renewable
Availability	Limited reserves, depleting fast	Available for 5 billion more years
Pollution	Causes air pollution (CO₂, SOx, NOx)	No pollution in energy production
Storage	Stores ancient solar energy in chemical form	Provides direct energy
Usage	Easily used for transport, electricity, industries	Requires solar panels or thermal systems

5. Compare and contrast bio-mass and hydro electricity as sources of energy.

✅ Answer:

Feature	Bio-Mass	Hydro Electricity
Nature	Renewable (if managed well)	Renewable
Source	Organic matter (wood, dung, crop waste)	Flowing water in rivers
Energy Conversion	Converts chemical energy to heat	Converts potential energy to electricity
Pollution	Produces smoke & CO₂	No air pollution but affects ecosystems
Efficiency	Low (inefficient burning)	High (80-90% efficiency)
Availability	Depends on agricultural waste & livestock	Limited to places with large water bodies

6. What are the limitations of extracting energy from—

(a) the wind?

✅ Answer:

Requires consistent wind speeds (above 15 km/h).
Not reliable – No electricity when the wind is calm.
Wind turbines require large land areas.

(b) waves?

✅ Answer:

Only viable in coastal regions with strong waves.
Expensive to set up and maintain.
Waves are not constant throughout the year.

(c) tides?

✅ Answer:

Needs specific coastal locations with high tidal ranges.
Dams can disrupt marine life and fishing activities.
High setup costs and complex infrastructure required.

7. On what basis would you classify energy sources as—

(a) renewable and non-renewable?

✅ Answer:

Renewable: Can be replenished naturally (Solar, Wind, Hydro, Bio-mass).
Non-renewable: Limited supply, takes millions of years to form (Coal, Petroleum, Nuclear).

(b) exhaustible and inexhaustible?

✅ Answer:

Exhaustible: Can be depleted (Fossil fuels, Nuclear energy).
Inexhaustible: Never runs out (Solar, Wind, Tidal energy).

✅ Are the options in (a) and (b) the same?

Not exactly. Some renewable sources (Bio-mass) can become exhaustible if overused.

8. What are the qualities of an ideal source of energy?

✅ Answer:
An ideal energy source should be:
✔️ Highly efficient – Provides a large amount of energy per unit.
✔️ Easily available – Accessible to everyone.
✔️ Non-polluting – Causes minimal environmental damage.
✔️ Renewable & Sustainable – Should last for future generations.
✔️ Affordable – Low cost of extraction and maintenance.

9. What are the advantages and disadvantages of using a solar cooker? Are there places where solar cookers would have limited utility?

✅ Answer:

✔️ Advantages:

Uses free & renewable solar energy.
Eco-friendly, produces no smoke or pollution.
Low maintenance cost.

❌ Disadvantages:

Works only during daytime and requires direct sunlight.
Slow cooking process compared to traditional methods.
Not suitable in cloudy or cold regions (e.g., polar regions, dense forests).

10. What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?

✅ Answer:

Environmental Consequences:

1️⃣ Deforestation – Cutting trees for bio-mass & land for energy projects.
2️⃣ Air & Water Pollution – Fossil fuels emit CO₂, SOx, and NOx, leading to acid rain and global warming.
3️⃣ Resource Depletion – Coal, oil, and gas reserves are running out.
4️⃣ Ecosystem Destruction – Dams submerge forests and affect biodiversity.
5️⃣ Nuclear Waste – Radioactive waste is hazardous and difficult to dispose of safely.

Steps to Reduce Energy Consumption:

✔️ Use energy-efficient appliances (LED bulbs, solar heaters).
✔️ Reduce fossil fuel use – Shift to renewable sources.
✔️ Practice conservation – Turn off unnecessary lights and fans.
✔️ Use public transport to reduce fuel consumption.
✔️ Promote afforestation to absorb CO₂ and improve air quality.

🌍 Sustainable energy use = A cleaner and healthier future! ♻️💡

Chapter 14 : Sources of Energy

14.1 WHAT IS A GOOD SOURCE OF ENERGY?

Introduction

Forms of Energy in Daily Life

Characteristics of a Good Source of Energy

Factors Affecting Choice of Energy Source

Questions to Consider When Choosing a Fuel

Conclusion

Q U E S T I O N S & A N S W E R S

1. What is a good source of energy?

2. What is a good fuel?

3. If you could use any source of energy for heating your food, which one would you use and why?

14.2 CONVENTIONAL SOURCES OF ENERGY

Introduction

14.2.1 Fossil Fuels

Importance of Fossil Fuels

Disadvantages of Fossil Fuels

How to Reduce Fossil Fuel Pollution?

14.2.2 Thermal Power Plants

14.2.3 Hydro Power Plants

Advantages of Hydro Power Plants

Disadvantages of Hydro Power Plants

Examples of Hydro Power Projects in India

14.2.4 Improvements in Technology for Conventional Sources of Energy

Bio-Mass

Bio-Mass Fuel Types

Advantages of Bio-Gas

14.2.5 Wind Energy

Working of Windmills

Advantages of Wind Energy

Limitations of Wind Energy

Wind Energy in India

Conclusion

Q U E S T I O N S & A N S W E R S

1. What are the disadvantages of fossil fuels?

2. Why are we looking at alternate sources of energy?

3. How has the traditional use of wind and water energy been modified for our convenience?

14.3 ALTERNATIVE OR NON-CONVENTIONAL SOURCES OF ENERGY

Introduction

14.3.1 Solar Energy ☀️

Ways to Harness Solar Energy

14.3.2 Energy from the Sea 🌊

Tidal Energy

Wave Energy

Ocean Thermal Energy (OTE)

14.3.3 Geothermal Energy 🌋

14.3.4 Nuclear Energy ☢️

Nuclear Fission Process

Advantages of Nuclear Energy

Disadvantages of Nuclear Energy

Nuclear Power Plants in India

14.3.5 Nuclear Fusion (Future Energy Source) ⚛️

Comparison of Alternative Energy Sources

Conclusion

Q U E S T I O N S & A N S W E R S

1. What kind of mirror – concave, convex or plane – would be best suited for use in a solar cooker? Why?

2. What are the limitations of the energy that can be obtained from the oceans?

3. What is geothermal energy?

4. What are the advantages of nuclear energy?

14.4 ENVIRONMENTAL CONSEQUENCES

Introduction

Environmental Impact of Different Energy Sources

Key Environmental Concerns

1️⃣ Air Pollution

2️⃣ Climate Change & Global Warming

3️⃣ Land Degradation & Deforestation

4️⃣ Water Pollution & Scarcity

5️⃣ Radioactive Waste

Finding the Best Energy Source 🔎

Conclusion

Q U E S T I O N S & A N S W E R S

1. Can any source of energy be pollution-free? Why or why not?

2. Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not?

14.5 HOW LONG WILL AN ENERGY SOURCE LAST US?

Introduction

Types of Energy Sources

1️⃣ Exhaustible (Non-Renewable) Sources

2️⃣ Inexhaustible Sources

3️⃣ Renewable Sources

4️⃣ Non-Renewable Sources