Physics in everyday life, technology and the environment
What this domain tests
This domain asks you to apply mechanics, electricity and heat to appliances, homes, transport, energy production and pollution. Typical tasks are electricity-bill calculations, efficiency comparisons, and reasoned arguments about energy sources and their environmental effects.
Core rules
- Energy is conserved but degraded. Every transformation turns part of the energy into low-temperature heat that can no longer be used; "energy used" always means "converted".
- Power and energy: E = Pt. A kilowatt-hour is the energy of a 1 kW appliance running for one hour (3.6 MJ); cost = energy × price per kWh.
- Efficiency: useful output / total input × 100 %. Electric heating is effectively 100 % efficient inside a room, but a power station converting fuel to electricity reaches only about 35–45 %; an incandescent bulb turns roughly 5 % of its energy into light while an LED reaches about 50 %.
- Household electricity: a 230 V, 50 Hz supply; fuses and circuit breakers protect the wiring, not the person; earthing and residual-current devices protect people; extension leads must not be overloaded, since P = UI.
- Buildings: thick insulation, triple glazing and draught-proofing reduce conduction and convection, but some ventilation is still needed for air quality and moisture.
- Transport: kinetic energy grows with v², so braking distance roughly quadruples when speed doubles, and reaction distance adds to it; seat belts and crumple zones lengthen the stopping time and so reduce the force.
- Environment: burning fossil fuels releases CO₂, SO₂ and particulates; renewables include wind, solar, hydro and biomass; nuclear power gives low-carbon electricity but leaves long-lived waste; noise and light pollution also count as environmental impacts.
Worked example
A 2.0 kW electric heater runs 4 hours a day for 30 days. Electricity costs 0.16 €/kWh. What is the cost?
E = 2.0 kW × 4 h/day × 30 days = 240 kWh. Cost = 240 × 0.16 = 38.40 €. The unit logic matters: power in kW multiplied by time in hours gives kWh directly; using watts would give 240 000 Wh, the same energy expressed differently.
Traps that cost marks
- Mixing kW and kWh, or W and kW, inside a bill calculation.
- Comparing appliances by power alone: a 2 kW kettle used for three minutes uses far less energy than a 100 W fridge running all day.
- Assuming a whole system is 100 % efficient because one part of it, such as an electric heater, is.
- Ignoring standby power when estimating household consumption.
- Claiming renewable sources have no environmental impact at all.
- Treating braking distance as proportional to speed instead of to speed squared.