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GCSE Combined Science
Physics (Combined Science)
Key physics topics: energy, electricity, forces, waves, and radioactivity.
In this topic
Energy
Energy cannot be created or destroyed, only transferred between stores. KE = ½mv², GPE = mgh, E = mcΔθ
Efficiency = (useful output / total input) × 100%
Energy resources: renewable (solar, wind, hydro, tidal, geothermal, biomass) and non-renewable (fossil fuels, nuclear).
Key Points
- Energy is always conserved
- Wasted energy is usually dissipated as heat
- Higher efficiency = less waste
- We need to reduce fossil fuel use to combat climate change
Example Questions
2A motor transfers 500 J of energy. 350 J is useful. Calculate the efficiency.
Efficiency = (350/500) × 100 = 70%
[2 marks]
Electricity
V = IR (Ohm's Law), P = IV, P = I²R, E = Pt, Q = It
Series: same current, voltage shared, R_total = R₁ + R₂ Parallel: same voltage, current shared, 1/R = 1/R₁ + 1/R₂
UK mains: 230V, 50Hz AC. Live (brown), Neutral (blue), Earth (green/yellow).
Key Points
- V = IR is the most important equation
- Power = energy per second (watts)
- Series: add resistances; Parallel: resistance decreases
- Earth wire is a safety feature
Example Questions
2Two 6Ω resistors are connected in parallel. Calculate the total resistance.
1/R = 1/6 + 1/6 = 2/6 = 1/3. R = 3Ω
[2 marks]