Environmental Physics, Energy and Climate
What this domain tests
This domain covers energy forms and units, thermodynamics, efficiency, renewable energy, radiation balance, albedo, the greenhouse effect and climate feedbacks. The exam tests calculations and distinctions between power, energy and climate forcing.
Core rules and concepts
- Energy is measured in joules (J); power is energy per time in watts (W). 1 kWh = 3.6 MJ.
- The first law of thermodynamics says energy is conserved; the second law says useful energy quality decreases in real conversions.
- Efficiency = useful output energy ÷ input energy × 100%.
- Solar radiation is absorbed, reflected or emitted; albedo is the reflected fraction. Greenhouse gases absorb and re-emit infrared radiation, warming the surface.
- The natural greenhouse effect makes Earth habitable; the enhanced greenhouse effect is the additional warming from human emissions.
Worked example
A solar panel receives 1,000 W m⁻² over 2 m², so input power = 2,000 W. At 15% efficiency, output = 0.15 × 2,000 = 300 W. Over 5 hours, energy = 300 W × 5 h = 1,500 Wh = 1.5 kWh. Reason: efficiency applies to power at each moment; multiplying by time gives energy. If the panel area were halved, output and daily energy would halve under the same conditions.
Traps that cost marks
Do not mix watts and watt-hours. Higher albedo means more reflection, not more absorption. The greenhouse effect is not inherently pollution; the problem is its enhancement. Climate feedbacks can be positive or negative. Energy efficiency does not mean energy is destroyed; it means less useful output is wasted.