Energy, Work And PowerCopy
Cheat Sheet: Energy, Work, Power & Efficiency (O Level / IGCSE Physics)
1.7.1 Energy
1. Forms of Energy Stores
- Kinetic – due to motion
- Gravitational Potential – due to position in a gravitational field
- Chemical – stored in fuel, food, batteries
- Elastic (strain) – in stretched or compressed objects
- Nuclear – stored in atomic nuclei
- Electrostatic – between electric charges
- Internal (thermal) – due to temperature and particle motion
2. Energy Transfers Between Stores
- Mechanical work – force moves an object (e.g. lifting, pushing)
- Electrical work – current flowing (e.g. circuits)
- Heating – energy moves due to temperature difference
- Waves – sound, electromagnetic radiation, etc.
Examples:
- Electric heater: electrical → thermal
- Pendulum: GPE ↔ KE
- Battery-powered motor: chemical → electrical → kinetic
3. Conservation of Energy
- Total energy is conserved (cannot be created or destroyed)
- Energy can only change forms or transfer between objects
4. Kinetic Energy
- Equation:
Eₖ = ½mv²
where:
Eₖ = kinetic energy (Joules, J)
m = mass (kg)
v = velocity (m/s)
5. Gravitational Potential Energy
- Equation:
∆Eₚ = m × g × ∆h
where:
∆Eₚ = change in GPE (J)
m = mass (kg)
g = gravitational field strength (9.8 N/kg)
∆h = change in height (m)
1.7.2 Work
- Definition: Energy transferred when a force moves an object
- Equation:
W = F × d
where:
W = work done (J)
F = force (N)
d = distance moved in direction of force (m)
1.7.3 Energy Resources
A. Types
Non-renewable:
- Fossil fuels (coal, oil, natural gas)
- Nuclear fuel
Renewable:
- Biofuels
- Hydroelectric
- Solar
- Geothermal
- Wind
- Tidal
- Wave
B. Energy Generation Methods
| Source | Conversion | Components |
|---|---|---|
| Fossil Fuels | Chemical → Thermal → Kinetic → Electrical | Boiler → Turbine → Generator |
| Biofuels | Same as fossil fuels (renewable) | Boiler → Turbine → Generator |
| Hydroelectric | GPE → Kinetic → Electrical | Water turns turbine → generator |
| Solar | Solar → Electrical (via solar panels) | No turbine needed |
| Nuclear | Nuclear → Thermal → Kinetic → Electrical | Reactor → Boiler → Turbine → Generator |
| Geothermal | Thermal → Kinetic → Electrical | Hot rocks → Steam → Turbine |
| Wind | Kinetic → Electrical | Blades turn turbine → generator |
| Tidal / Wave | Kinetic → Electrical | Water motion drives turbines |
C. Advantages and Disadvantages
| Method | Renewable? | Availability | Environmental Impact |
|---|---|---|---|
| Fossil Fuels | ❌ | Reliable | High pollution, CO₂ |
| Nuclear | ❌ | Reliable | Radioactive waste |
| Biofuels | ✅ | Seasonal | Some emissions |
| Hydroelectric | ✅ | Weather/river dependent | Can flood land |
| Solar | ✅ | Daylight only | Clean, but expensive |
| Geothermal | ✅ | Location-limited | Clean |
| Wind | ✅ | Variable | Visual/noise pollution |
| Tidal/Wave | ✅ | Predictable (tides) | Affects marine life |
1.7.4 Efficiency
- Definition: % of input energy or power that is usefully transferred
A. Equations
(a) Efficiency (energy) =
(useful energy output / total energy input) × 100%
(b) Efficiency (power) =
(useful power output / total power input) × 100%
1.7.5 Power
- Definition: Rate of doing work or transferring energy
A. Equations
(a) P = W / t
P = power (W)
W = work done (J)
t = time (s)
(b) P = ∆E / t
∆E = energy transferred (J)
t = time (s)