⚡️ Energy resources are the raw materials we use to produce energy. They can be renewable (like wind or solar) or non‑renewable (like coal or oil). Understanding how efficiently we can convert these resources into useful work is key to judging their value and environmental impact.
Efficiency, denoted by the Greek letter η, is the ratio of useful work output to the energy input. It is always expressed as a percentage.
\$\eta = \frac{W{\text{out}}}{Q{\text{in}}}\times 100\%\$
| Resource | Typical Efficiency | Example Use |
|---|---|---|
| Coal (fossil fuel) | 30–40 % | Electricity generation |
| Natural gas (fossil fuel) | 45–55 % | Power plants & heating |
| Solar PV panels | 15–22 % | Home electricity |
| Wind turbines | 35–45 % | Grid power |
| Hydroelectric dams | 70–90 % | Large‑scale electricity |
Imagine a water wheel turning in a river. The water’s kinetic energy is the input energy. The wheel’s rotation is the useful work output. If the wheel is made of a very slippery material, most of the water’s energy will just flow past – low efficiency. If it’s a well‑designed wheel with good paddles, most of the water’s energy turns the wheel – high efficiency. This is exactly how we think about energy conversion in power plants and engines.
💡 Tip for exams: When you see a question about efficiency, always write the formula, identify the work and heat terms, and remember that efficiencies are less than 100 % for real devices.
📝 Exam Tip: Always express your answer as a percentage and round to the nearest whole number unless the question specifies otherwise.