Bihar Board Class 10 · Science · Matric exam 2027
Chapter 14: Sources of Energy — notes
The chapter’s 8 parts in the book’s order — the first idea of each and the points Medha Ma’am writes on the board — and the summary at the end. The full lesson and a check question for each part are in the app.
1. Why we still face an energy crisis
Okay, so you already know energy is conserved.
- • Energy is conserved, but changes form
- • Candle: chemical energy -> heat + light
- • Hot water (348 K) cools to room temp (298 K)
- • Usable energy -> less usable energy, cannot be reused
2. What makes a good source of energy
Okay, so think about choosing a fuel, say for cooking food.
- • Good source of energy:
- • - large work per unit volume/mass
- • - easily accessible
- • - easy to store and transport
- • - economical
3. Fossil fuels and thermal, hydro power plants
Okay, so let's talk about fossil fuels.
- • Fossil fuels: coal, petroleum − non-renewable
- • Burning releases oxides of C, N, S -> acid rain
- • Thermal plant: fuel -> heat -> steam -> turbine -> electricity
- • Hydro plant: dam water potential energy -> turbine -> electricity
- • Hydro power is renewable (reservoir refilled by rain)
- • Problems: submerged land, displaced people, methane
4. Bio-mass and wind energy
Okay, so let's talk about bio-mass.
- • Bio-mass: wood, cow-dung cakes
- • Charcoal: wood burnt with limited O2, more heat
- • Bio-gas (gobar-gas): up to 75% methane, no smoke
- • Slurry left -> manure (rich in N and P)
- • Windmill: wind's kinetic energy -> turbine -> electricity
5. Solar energy
The Sun has been radiating energy at the present rate for nearly 5 billion years and will continue for about 5 billion years more; only part of this reaches earth after passing through the atmosphere.
- • Solar constant = 1.4 kJ/s/m2 = 1.4 kW/m2
- • Black surface absorbs more heat than white
- • Solar cooker: black box + glass plate (green-house effect)
- • Solar cell: 0.5-1 V, about 0.7 W per cell
- • Many cells combined -> solar cell panel
6. Energy from the sea and geothermal energy
Okay, so let's talk about energy from the sea.
- • Tidal energy: moon's pull -> tides -> dam + turbine
- • Wave energy: wind-driven waves -> turbine
- • Ocean thermal energy: needs temp difference of 20 K or more
- • Warm water boils ammonia -> vapour runs turbine
- • Geothermal energy: hot spots -> steam -> turbine
- • Hot springs: hot water reaching the surface
7. Nuclear energy
Nuclear energy is generated through nuclear fission, where the nucleus of a heavy atom like uranium, plutonium or thorium, when bombarded with low-energy neutrons, splits apart into lighter nuclei, releasing a tremendous amount of energy because the mass of…
- • Nuclear fission: heavy nucleus + neutron -> lighter nuclei + huge energy
- • Uranium fission gives 10 million × energy of carbon combustion
- • E = Δm c2 (Einstein's equation)
- • Chain reaction in reactor -> heat -> steam -> turbine -> electricity
- • Hazards: waste storage, radiation leakage, high cost
8. Renewable and non-renewable sources, and environment
Okay, so let's talk about the two kinds of energy sources.
- • Non-renewable (exhaustible): will get used up, e.g. fossil fuels
- • Renewable: can be regenerated, e.g. bio-mass
- • No source is completely pollution-free
- • Choice depends on: ease, cost, efficiency, environmental damage
- • Many sources ultimately derive energy from the Sun
Summary
Okay, so let's go over everything we've learned in this chapter. We started by saying energy is conserved, it never gets destroyed. But it changes into less usable forms, and that's why we say a source gets used up. Then we asked — what makes a source of energy a good one? We said it should give large work per unit mass or volume, it should be easy to access, easy to store and transport, and it should be economical. Among conventional sources, we looked at fossil fuels in thermal power plants, and falling water in hydro power plants. We also saw improved bio-mass fuels, like charcoal and bio-gas, and wind energy, used through windmills and wind farms. Then we moved to alternative sources. We saw solar energy, used in solar cookers and solar cells. We saw energy from the sea, through tidal energy, wave energy, and ocean thermal energy. We saw geothermal energy, coming from hot spots inside the earth, and nuclear energy, from fission. We also mentioned nuclear fusion, which is how the Sun produces its own energy. Finally, we said sources are either renewable or non-renewable, depending on whether they can be regenerated. No source is completely free of pollution. And almost every source, if you trace it back, comes from the Sun. So tell me — which source from today would you like to understand a little more?
AskMedha · Medha Ma’am — Bihar Board Class 10 Science, Chapter 14. Written from the textbook, checked twice.
Questions parents and students ask
- How do I get the "Sources of Energy" notes as a PDF?
- Press "Save as PDF" — the phone’s print sheet opens; choose "Save as PDF" there. The PDF holds the notes only.
- Where are these notes written from?
- From the chapter’s own textbook text, part by part, in the book’s own terms; a second, independent model then checked every part against the book. The full lesson, a check question for each part and the practice are in the AskMedha app.
The same preparation, with Medha Ma’am — on your phone
Every question of every chapter with its model answer, practice questions in the board’s own shapes, 60 minutes of class a day, written answers marked, a test every Sunday and a WhatsApp report to parents.
Medha Ma’am is an AI teacher, not a live tutor. Every answer is checked twice; a person takes responsibility.