In this unit we explore how useful energy can be extracted from different natural and man‑made sources. Think of each source as a different type of “fuel” that can be turned into electricity or heat. Below we break the topic into seven parts (a–g) and give you clear, exam‑ready notes with colourful boxes, emojis, and handy analogies.
Fossil fuels (coal, oil, natural gas) are like the “old food” of the planet. When they burn, the chemical bonds break and release heat:
Combustion reaction example:
\$\displaystyle \text{C}6\text{H}{12}\text{O}6 + 6\text{O}2 \rightarrow 6\text{CO}2 + 6\text{H}2\text{O} + \text{heat}\$
The heat boils water → steam → turbine → generator → electricity.
Exam tip: Remember the sequence: combustion → heat → steam → turbine → generator. Use the word “boiler” when describing the water‑to‑steam step.
Biofuels (ethanol, biodiesel) come from living plants. They contain stored chemical energy just like fossil fuels, but they are renewable because plants absorb CO₂ while growing.
Example: \$\displaystyle \text{C}2\text{H}5\text{OH} + 3\text{O}2 \rightarrow 2\text{CO}2 + 3\text{H}_2\text{O} + \text{heat}\$
The heat can again be used to produce steam for a turbine or to directly power engines.
Exam tip: Highlight that biofuels are renewable and that the carbon cycle is closed (plants absorb CO₂, engines emit CO₂).
Hydroelectric dams: Water stored behind a dam has potential energy \$E_p = mgh\$. When released, it flows through a turbine → spins a generator → produces electricity.
Wave & tide power: Moving water exerts kinetic energy \$E_k = \tfrac{1}{2}mv^2\$. Devices capture this energy similarly to a turbine.
Analogy: Think of a water wheel in a stream – the falling water pushes the wheel, just like a turbine.
Exam tip: Use the formula \$E_p = mgh\$ for potential energy. Remember that \$h\$ is the height of the water drop.
Heat from the Earth’s interior can be tapped by drilling deep wells. Hot water or steam rises, drives a turbine, and generates electricity.
Key point: The energy comes from the planet’s internal heat, not from the Sun.
Analogy: Imagine a giant kettle under the ground heating up the water inside.
Exam tip: Note that geothermal power is continuous because the Earth’s heat is steady.
Nuclear fission splits heavy nuclei (e.g., U‑235) into lighter ones, releasing a huge amount of energy:
\$\displaystyle \text{U}^{235} \rightarrow \text{Ba}^{141} + \text{Kr}^{92} + 3\text{n} + \text{energy}\$
The energy heats water → steam → turbine → generator.
Analogy: Think of a “super‑fast” chain reaction, like a domino effect that releases a lot of heat.
Exam tip: Remember that nuclear power is non‑renewable but produces no CO₂.
Solar cells convert light directly into electricity via the photovoltaic effect. When photons hit the cell, they knock electrons free, creating a current.
\$\displaystyle \text{Photon energy} \; (h\nu) \geq \text{band gap}\$
Analogy: Like a tiny solar-powered battery that charges when the sun shines.
Exam tip: Use the phrase “photovoltaic effect” and remember that efficiency depends on the band gap of the semiconductor.
Solar thermal panels absorb infrared and other EM waves, heating water in a boiler. The hot water turns into steam, which drives a turbine and generator.
Key components:
Analogy: Think of a giant kettle that the Sun heats up, turning water into steam to spin a wheel.
Exam tip: Emphasise the role of the boiler and turbine in the conversion chain.
| Source | Key Energy Form | Main Conversion Step | Renewable? |
|---|---|---|---|
| Fossil Fuels | Chemical (combustion) | Boiler → Turbine → Generator | No |
| Biofuels | Chemical (combustion) | Boiler → Turbine → Generator | Yes |
| Hydro | Potential (water) | Turbine → Generator | Yes |
| Geothermal | Thermal (Earth) | Boiler → Turbine → Generator | Yes |
| Nuclear | Fission (chemical) | Boiler → Turbine → Generator | No |
| Solar PV | Electrical (photovoltaic) | Direct conversion to electricity | Yes |
| Solar Thermal | Thermal (infrared) | Boiler → Turbine → Generator | Yes |
Final Exam Tip: When answering questions, always: