Towards Green Energy Class 10 Notes, Formulas, Questions | SSC

This chapter explains how electrical energy is generated using the principle of electromagnetic induction, with a turbine driving a generator. It describes thermal, nuclear and natural gas power plants, their energy transformations and their problems. It then explains why the world is moving towards green energy and how hydroelectric, wind and solar energy are used to produce electricity, including calculations with solar cells and panels.

Summary

Energy has become a basic need along with food, clothing and shelter, and we use it as mechanical, chemical, sound, light and heat energy. Energy can be converted from one form to another. Most power plants work on Michael Faraday's principle of electromagnetic induction: when the magnetic field around a conductor changes, a potential difference is produced across it. The field can be changed by rotating a magnet near a fixed conductor or by moving a conductor in a fixed field. A machine based on this principle is an electric generator.

In large power plants a turbine rotates the magnet of the generator. A turbine has blades that rotate when a stream of liquid or gas strikes them, using the kinetic energy of the flow. So electricity generation needs an energy source to drive the turbine, the turbine to rotate the generator and the generator to produce electricity. Power stations are named after the energy source used, and their turbine designs differ.

In a thermal power plant, coal is burnt in a boiler to make steam at very high temperature and pressure. The steam turns the turbine, which drives the generator. The used steam is cooled back to water in a condenser using water from the cooling tower and returned to the boiler, while combustion gases leave through a tall stack. The energy changes are chemical energy in coal to thermal energy to kinetic energy of steam to kinetic energy of the turbine to electrical energy. Problems are air pollution from CO2, sulphur oxides and nitrogen oxides, soot that harms the respiratory system, and limited coal reserves.

A nuclear power plant also uses a steam turbine, but the heat comes from fission of uranium or plutonium nuclei. When U-235 absorbs a neutron it becomes unstable U-236, which splits into barium and krypton, releasing three neutrons and about 200 MeV of energy. These neutrons split more U-235 nuclei, giving a chain reaction, which is kept controlled in a reactor. Nuclear power causes no air pollution from burning fuel, but nuclear waste is radioactive and hard to dispose of safely, and accidents can release very harmful radiation.

In a natural gas power plant, a compressor feeds pressurised air into a combustion chamber where natural gas burns, producing gas at very high temperature and pressure that drives a gas turbine and the generator. Its efficiency is higher than that of a coal plant, and since natural gas has no sulphur it pollutes less. Still, burning fossil fuels emits gases and soot; carbon monoxide from incomplete combustion harms health, extra CO2 causes global warming, nitrogen dioxide causes acid rain, and soot causes respiratory problems like asthma. Fossil fuels took millions of years to form and are limited: coal may last about 200 years and natural gas about 200 to 300 years at current use. For these reasons energy from fossil and nuclear fuels is not environment friendly.

Green energy is electricity produced from perpetual sources like water reservoirs, wind, sunlight and biofuels, which do not cause the problems above. In a hydroelectric plant, the potential energy of water stored in a dam becomes kinetic energy of flowing water, which turns the turbine and generator; water is usually drawn from about the middle height of the dam. Advantages are no pollution from burning fuel, generation whenever needed if water is stored, and refilling of the reservoir in the rainy season. Problems are submergence of villages, forests and fertile land, rehabilitation of displaced people and harm to river life, so whether it is truly eco-friendly is debated.

A wind turbine converts kinetic energy of wind into electrical energy: wind turns the blades, and the axle drives the generator through a gear box that increases the rotations per unit time. Turbines from below 1 kW to about 7 MW are available, chosen according to local wind speed. Seashores have high wind speeds. Wind energy is clean, but suitable wind speed is not available everywhere, so its use is limited.

Solar energy gives electricity in two ways. Solar photovoltaic cells, made of semiconductors like silicon, convert sunlight directly into DC electricity without a generator; a 1 square cm silicon cell gives about 30 mA at about 0.5 V, and the voltage does not depend on area. Cells in series add voltages with the same current, and cells in parallel add currents with the same voltage. Cells form panels, panels in series form strings and strings in parallel form arrays; a good cell is about 15 percent efficient. An inverter converts DC to AC, batteries store energy for night use, and solar cells work only in daytime. In a solar thermal plant, reflectors concentrate sunlight on an absorber, the heat makes steam, and the steam drives a turbine and generator.

Mind map

Energy transformation in a thermal power plant

Important definitions

Formulas

Key points to remember

• Most power plants work on electromagnetic induction discovered by Michael Faraday.
• Energy source drives turbine, turbine drives generator, generator gives electricity.
• Thermal plant: chemical, thermal, kinetic (steam), kinetic (turbine), electrical energy.
• Nuclear plant: nuclear, thermal, kinetic (steam), kinetic (turbine), electrical energy.
• Hydroelectric plant: potential energy of water, kinetic energy of water, kinetic energy of turbine, electrical energy.
• Wind plant: kinetic energy of wind, kinetic energy of turbine, electrical energy; a gear box increases rotations.
• Solar photovoltaic cells need no generator and give DC electricity.
• Natural gas contains no sulphur, so gas plants pollute less and are more efficient than coal plants.
• Coal reserves may last about 200 years and natural gas about 200 to 300 years at current use.
• Coal gives about 60 percent of India's electricity and 41 percent of the world's, as per the textbook table.
• Wind turbines are available from under 1 kW to about 7 MW.
• Many solar panels in series form a string; strings in parallel form an array.
• Koyna (Maharashtra, 1960 MW) and Tehri (Uttarakhand, 2400 MW) are major hydroelectric plants; Chandrapur (3340 MW) is a major thermal plant in Maharashtra.

Solved examples

Example 1. Find the current and voltage from a silicon solar cell of area 100 square cm.

Current = 30 mA per square cm x 100 square cm = 3000 mA = 3 A. Voltage stays about 0.5 V since it does not depend on area. Answer: 3 A at 0.5 V.

Example 2. 36 solar cells, each of area 100 square cm, are connected in series in a panel. Find the voltage, current and power of the panel.

In series voltages add: V = 36 x 0.5 = 18 V. Current stays that of one cell: I = 3 A. Power P = V x I = 18 x 3 = 54 W.

Example 3. A solar panel gives 18 V and 3 A. How can you obtain 72 V and 9 A using such panels?

Voltage: 72 / 18 = 4, so connect 4 panels in series to make one string of 72 V and 3 A. Current: 9 / 3 = 3, so connect 3 such strings in parallel. The array gives 72 V and 9 A and needs 4 x 3 = 12 panels.

Example 4. A solar panel receives 100 W of solar power and has efficiency 15 percent. What is its electrical output?

Output = efficiency x input = (15 / 100) x 100 W = 15 W.

Example 5. Two solar cells of 0.5 V and 2 A each are connected (a) in series, (b) in parallel. Find the output in each case.

(a) Series: V = 0.5 + 0.5 = 1 V, I = 2 A. (b) Parallel: V = 0.5 V, I = 2 + 2 = 4 A.

Example 6. In the first step of a chain reaction one U-235 fission releases 3 neutrons, and each causes another fission. How many fissions occur in the third step, and how much energy do they release?

Step 1: 1 fission. Step 2: 3 fissions. Step 3: 3 x 3 = 9 fissions. Energy in step 3 = 9 x 200 MeV = 1800 MeV.

Important questions and answers

Q1. What is meant by green energy? Which sources are green energy sources and why?

Energy produced without causing environmental problems like pollution, and from sources that never run out, is green energy. Water reservoirs (hydro), wind, sunlight and biofuels are green energy sources because they are perpetual and generating electricity from them involves no fuel combustion, so no harmful gases or soot are released.

Q2. Give reasons: The construction of turbines is different for different types of power plants.

The turbine is driven by different energy sources in different plants: high-pressure steam in thermal and nuclear plants, hot gas in gas plants, flowing water in hydroelectric plants and wind in wind plants. The pressure, speed and nature of these flows differ, so turbines are designed differently to use each efficiently.

Q3. Give reasons: It is absolutely necessary to control the fission reaction in nuclear power plants.

Each fission releases three neutrons that cause more fissions, so the number of fissions and the energy released grow very fast. An uncontrolled chain reaction can release enormous energy at once and cause a disastrous accident with release of harmful radiation, so it must be controlled to release heat steadily for generating electricity.

Q4. Give reasons: Hydroelectric, solar and wind energy are called renewable energies.

Their sources never run out: rainfall refills reservoirs every year, the Sun shines daily and winds blow continuously. Unlike coal or natural gas, they are not used up, so they are renewable.

Q5. Give reasons: It is possible to produce energy from mW to MW using solar photovoltaic cells.

A single small cell gives a tiny output, enough for devices like solar calculators. By connecting many cells in series and parallel into panels, strings and arrays, the voltage and current can be increased to any required level, up to power stations of MW capacity.

Q6. Explain the step-by-step energy conversion in a nuclear power plant.

Nuclear energy released by fission of uranium or plutonium in the reactor becomes thermal energy, which converts water into high-pressure steam. The kinetic energy of steam turns the turbine, and the kinetic energy of the turbine runs the generator, giving electrical energy. Steam is condensed and recycled.

Q7. Explain the step-by-step energy conversion in a hydroelectric power plant.

Water stored in the dam has potential energy. When it flows down through the penstock this becomes kinetic energy of flowing water, which turns the water turbine. The kinetic energy of the turbine drives the generator, producing electrical energy.

Q8. Distinguish between thermal electricity generation and solar thermal electricity generation.

Thermal power plants get heat by burning coal; solar thermal plants get heat by concentrating sunlight with reflectors on an absorber. Thermal plants cause air pollution and use limited fuel; solar thermal plants cause no fuel combustion pollution and use a perpetual source. Thermal plants work day and night; solar thermal plants depend on sunlight. Both use steam to run a turbine and generator.

Q9. Distinguish between conventional and non-conventional sources of energy.

Conventional sources like coal, petroleum and natural gas have long been used on a large scale, are limited and cause pollution. Non-conventional sources like solar, wind and biofuel energy are newer in large-scale use, are perpetual and are environment friendly. Hydroelectric energy is a conventional source but renewable.

Q10. What are the advantages and limitations of solar energy?

Advantages: no fuel is burnt, so there is no air pollution; the source is perpetual; output can be scaled from mW to MW; DC can be used directly for LED lights. Limitations: electricity is produced only in daytime, so batteries are needed for storage; it is DC and needs an inverter for AC equipment; efficiency of a good cell is only about 15 percent.

Q11. Write a short note on electrical energy generation and environment.

Burning coal and natural gas releases gases and soot causing air pollution; CO harms health, CO2 adds to global warming, nitrogen dioxide causes acid rain and soot causes asthma. Fossil fuels are limited and will deplete. Nuclear plants create radioactive waste and risk of accidents. Hence these methods are not environment friendly, and the world is turning to green energy from water, wind, sunlight and biofuels.

Q12. What are the problems associated with hydroelectric power plants?

Back-water of dams may submerge villages and towns, leading to rehabilitation problems for displaced people. Forests and fertile land may also be submerged. Obstructing river flow can harm living organisms in the river. Hence it is debated whether hydroelectricity is fully environment friendly.

Exam tips

• Draw the energy transformation chain as a neat flow diagram for each type of plant.
• In solar sums, add voltages for series and currents for parallel; never mix them.
• Remember that solar cell voltage does not depend on its area; only current does.
• Learn the problems of each plant type: pollution and limited coal for thermal, waste and accidents for nuclear, displacement for hydro, limited sites for wind, daytime only for solar.
• Label the stack, boiler, turbine, generator, condenser and cooling tower in the thermal plant schematic.

FAQs

Which type of power plant does not use electromagnetic induction?

Solar photovoltaic plants, which convert sunlight directly into electricity without a generator.

Why is a gear box used in a wind turbine?

To increase the number of rotations per unit time given to the generator.

Is hydroelectric energy green energy?

It causes no fuel-burning pollution and uses a renewable source, but submergence, displacement and harm to river life make its eco-friendliness debatable.

Why does a solar power station need an inverter?

Solar cells give DC power, while most domestic and industrial equipment runs on AC.

These notes were prepared with AI help from the Balbharati Science and Technology Part 2 textbook (2026-27) and checked against it.