🔋 1.7.1 Energy
🔹 What is Energy?
Energy = the ability to do work.
🔹 Forms of Energy (Energy Stores)
You must be able to state and recognize these:
| Energy Store | Description | Example |
|---|---|---|
| Kinetic (Ek) | Energy of motion | Moving car |
| Gravitational Potential (Ep) | Due to height | Book on a shelf |
| Chemical | Stored in substances | Fuel, food, batteries |
| Elastic (Strain) | Stored when stretched/compressed | Spring, rubber band |
| Nuclear | Stored in atomic nuclei | Uranium |
| Electrostatic | Between charged objects | Charged balloon |
| Internal (Thermal) | Due to particle motion | Hot object |
🔹 Energy Transfers
Energy moves between stores during processes:
Methods of Energy Transfer:
- Mechanical work (forces)
→ e.g. pushing a box - Electrical work (current)
→ e.g. battery powering a bulb - Heating
→ e.g. kettle warming water - Waves
- Light (electromagnetic)
- Sound
- Other waves
Example:
A falling ball:
- Gravitational potential → Kinetic energy
🔹 Conservation of Energy
Principle:
Energy cannot be created or destroyed, only transferred or transformed.
Example:
Light bulb:
- Electrical → Light + Heat (wasted)
🔹 Energy Equations
1. Kinetic Energy:
- (m) = mass (kg)
- (v) = velocity (m/s)
Example:
A 2 kg object moving at 3 m/s:
2. Gravitational Potential Energy:
Example:
2 kg lifted 5 m:
🔹 Sankey Diagrams
Used to show energy transfers.
- Width of arrows = amount of energy
- Show useful vs wasted energy
Example:
Electrical → Light (useful) + Heat (wasted)
📝 Exam Tips:
- Always mention wasted energy is usually heat
- Use correct units (Joules)
- Clearly state energy transfer, not just energy type
⚙️ 1.7.2 Work
🔹 What is Work Done?
Work done = energy transferred
🔹 Equation:
- (W) = work (J)
- (F) = force (N)
- (d) = distance (m)
Example:
Force = 10 N, distance = 5 m:
Key Idea:
- If no movement, no work done
- e.g. pushing a wall
📝 Exam Tips:
- Distance must be in direction of force
- Always include units: J (joules)
🌍 1.7.3 Energy Resources
🔹 Types of Energy Resources
1. Fossil Fuels (coal, oil, gas)
- Energy from chemical energy
- Used in boiler → steam → turbine → generator
2. Biofuels
- From plants/organic matter
- Renewable but may compete with food supply
3. Water Energy
- Hydroelectric dams
- Tides
- Waves
4. Geothermal
- Heat from Earth’s interior
5. Nuclear Fuel
- Energy from nuclear reactions (fission)
6. Solar Cells
- Convert sunlight → electricity
7. Solar Panels (thermal)
- Sun → heats water
🔹 Energy Generation System (Common Process)
In many systems:
- Fuel → heats water (boiler)
- Steam spins turbine
- Turbine drives generator → electricity
🔹 Advantages & Disadvantages
| Source | Advantages | Disadvantages |
|---|---|---|
| Fossil fuels | Reliable, high output | Non-renewable, pollution |
| Biofuels | Renewable | Uses farmland |
| Hydroelectric | Clean, renewable | Expensive, floods land |
| Wind | Renewable | Unreliable |
| Solar | Renewable | Weather dependent |
| Nuclear | High energy output | Radioactive waste |
🔹 Efficiency
Definition:
Example:
Input = 200 J, useful = 50 J:
Key Idea:
- Efficiency always < 100%
- Energy is lost as heat and sound
🔹 Important Facts:
- Sun is the main energy source for:
- Fossil fuels
- Wind
- Waves
- Biofuels
Exceptions:
- Geothermal
- Nuclear
- Tidal
🔹 Nuclear Fusion
- Occurs in the Sun
- Releases huge energy
- Scientists researching it for electricity
📝 Exam Tips:
- Be ready to compare energy sources
- Mention:
- Renewability
- Reliability
- Environmental impact
⚡ 1.7.4 Power
🔹 What is Power?
Power = rate of doing work / energy transfer per second
🔹 Equations:
1. Power from work:
2. Power from energy:
- (P) = power (Watts, W)
- (t) = time (seconds)
Example:
Work = 100 J, time = 5 s:
Key Idea:
- More power = faster energy transfer
📝 Exam Tips:
- Unit of power = Watt (W)
- 1 W = 1 J/s
- Always check time is in seconds
⭐ Final Summary (Quick Revision)
- Energy = ability to do work
- Work done = energy transferred
- Power = rate of energy transfer
- Energy is conserved
- Efficiency shows how useful a system is