CDS Physics · Free notes
Energy Sources: CDS Physics
Energy Sources has 5 past-year questions in CDS General Knowledge, from 2017 (II) to 2023 (I): 3 EASY and 2 MODERATE. None of them needs a calculation. Biogas has come up twice, once for what it is made of and once for whether it is renewable, and the other three ask about solar energy, the thermal power station and the glass greenhouse. It is a short, one-page chapter: learn which sources are renewable, what biogas contains, and why glass traps the Sun's heat.
The handout has every subtopic, worked example, formula and trap with answers shown. The formula sheet is the chapter’s formulas and traps alone, on one page.
Subtopic notes
Formula & revision sheet
0 formulas · 3 reference tables · 3 gotchas across all subtopics — the exam-eve cheat-sheet
Formula & revision sheet
0 formulas · 3 reference tables · 3 gotchas across all subtopics — the exam-eve cheat-sheet
Reference tables (3)
Conventional and non-conventional sources5 rows
| Source | Kind |
|---|---|
| Coal | Conventional, non-renewable |
| Petroleum and natural gas | Conventional, non-renewable |
| Solar energy | Non-conventional, renewable |
| Wind, tides and geothermal heat | Non-conventional, renewable |
| Thermal power station | Burns fuel to raise steam that spins a turbine and generatorQ CDS 2023 (I): fuel heats water to steam, which drives the turbine; that is how the station makes electricity. |
Biogas5 rows
| Property of biogas | Fact |
|---|---|
| Main gas | Methane, about 55 to 75 per cent |
| Second gas | Carbon dioxide |
| How it is formed | Anaerobic decomposition of dung and waste |
| Renewable or not | RenewableQ CDS 2022 (I): the false statement about biogas is that it is non-renewable. |
| Leftover slurry | Used as manure |
Solar heating and the greenhouse effect4 rows
| Device or effect | How it uses sunlight |
|---|---|
| Glass greenhouse | Lets short-wavelength sunlight in, traps long-wavelength infrared |
| Box-type solar cooker | Black inside to absorb, glass lid to trap heat, mirror to reflect light in |
| Solar cell | Sunlight to electricity directly; made of silicon |
| Solar water heater | Black pipes absorb heat and warm the water |
Watch out for (3)
- Fossil fuels are conventional and exhaustible→ Conventional and non-conventional sources
- Biogas is methane with carbon dioxide→ Biogas
- Glass lets short waves in and keeps long waves out→ Solar heating and the greenhouse effect
PYQ weightage by concept
3 concepts · 5 PYQs — where the marks actually sit, so you know what to drill first
PYQ weightage by concept
3 concepts · 5 PYQs — where the marks actually sit, so you know what to drill first
| Concept | PYQs | Share |
|---|---|---|
| Conventional and non-conventional sources | 2 | 40% |
| Biogas | 2 | 40% |
| Solar heating and the greenhouse effect | 1 | 20% |
Test yourself on a real paper
Sit a past CDS paper, timed and marked the way the exam marks it. You see your score and every answer the moment you finish. Free to start.