3.2 Energy Applications & Efficiency
What is Efficiency?
When energy is transferred, some is always dissipated (wasted), usually as heat or sound. Efficiency measures how much of the total energy input is transferred into useful energy output.
When energy is transferred, some is always dissipated (wasted), usually as heat or sound. Efficiency measures how much of the total energy input is transferred into useful energy output.
⚡ Efficiency Formula:
$$\text{Efficiency} = \frac{\text{Useful Energy Output}}{\text{Total Energy Input}}$$
Or using power:
$$\text{Efficiency} = \frac{\text{Useful Power Output}}{\text{Total Power Input}}$$
• Efficiency has no units
• Can be given as a decimal (0.60) or percentage (60%)
• Multiply decimal by 100 to get percentage
Or using power:
$$\text{Efficiency} = \frac{\text{Useful Power Output}}{\text{Total Power Input}}$$
• Efficiency has no units
• Can be given as a decimal (0.60) or percentage (60%)
• Multiply decimal by 100 to get percentage
Energy In
100 J
Total input
Useful Out
20 J
Light energy
Wasted
80 J
Heat energy
Example 1: Light Bulb Efficiency
A light bulb uses 100 J of electrical energy and produces 20 J of light energy. Calculate its efficiency.
Step 1: Write the formula
$\text{Efficiency} = \frac{\text{Useful Output}}{\text{Total Input}}$
Step 2: Substitute values
$\text{Efficiency} = \frac{20}{100} = 0.20$
Step 3: Convert to percentage
$0.20 \times 100 = 20\%$
Answer: The bulb is 20% efficient. The other 80 J is wasted as heat.
Step 1: Write the formula
$\text{Efficiency} = \frac{\text{Useful Output}}{\text{Total Input}}$
Step 2: Substitute values
$\text{Efficiency} = \frac{20}{100} = 0.20$
Step 3: Convert to percentage
$0.20 \times 100 = 20\%$
Answer: The bulb is 20% efficient. The other 80 J is wasted as heat.
■ Useful (Light)
■ Wasted (Heat)
Example 2: Finding Useful Output
A motor is 75% efficient and uses 800 J of electrical energy. How much useful kinetic energy does it produce?
Step 1: Convert percentage to decimal
$75\% = 0.75$
Step 2: Rearrange the formula
$\text{Useful Output} = \text{Efficiency} \times \text{Total Input}$
Step 3: Calculate
$\text{Useful Output} = 0.75 \times 800 = 600$ J
Answer: 600 J of useful kinetic energy
Step 1: Convert percentage to decimal
$75\% = 0.75$
Step 2: Rearrange the formula
$\text{Useful Output} = \text{Efficiency} \times \text{Total Input}$
Step 3: Calculate
$\text{Useful Output} = 0.75 \times 800 = 600$ J
Answer: 600 J of useful kinetic energy
💡 Improving Efficiency:
We can increase efficiency by reducing wasted energy:
• Lubrication: Reduces friction in engines and machines
• Insulation: Reduces heat loss in buildings
• Streamlining: Reduces air resistance in vehicles
• LED bulbs: Convert more energy to light than filament bulbs
• Better materials: Reduce energy losses
• Lubrication: Reduces friction in engines and machines
• Insulation: Reduces heat loss in buildings
• Streamlining: Reduces air resistance in vehicles
• LED bulbs: Convert more energy to light than filament bulbs
• Better materials: Reduce energy losses
Typical Efficiencies:
| Device | Efficiency | Main Waste |
|---|---|---|
| LED light bulb | ~90% | Heat |
| Electric motor | ~85% | Heat, sound |
| Gas boiler | ~90% | Heat (exhaust) |
| Car engine | ~25% | Heat, sound |
| Filament bulb | ~5% | Heat |
🧮 Efficiency Calculator:
Useful output:
J
Total input:
J
🎯 Efficiency Practice
Types of Energy Resources
We use energy resources for transport, heating, and generating electricity. They can be split into two groups: renewable and non-renewable.
• Can be replenished naturally
• Often weather-dependent
• Lower carbon emissions
• Higher setup costs
• Formed over millions of years
• Reliable (not weather-dependent)
• Release greenhouse gases
• Currently cheaper
Renewable Energy Resources:
Non-Renewable Energy Resources:
We use energy resources for transport, heating, and generating electricity. They can be split into two groups: renewable and non-renewable.
Renewable
• Will not run out• Can be replenished naturally
• Often weather-dependent
• Lower carbon emissions
• Higher setup costs
Non-Renewable
• Will eventually run out• Formed over millions of years
• Reliable (not weather-dependent)
• Release greenhouse gases
• Currently cheaper
Solar
Energy from sunlight
Wind
Wind turbines
Hydroelectric
Moving water in dams
Tidal
Flow of tides
Geothermal
Heat from Earth
Biofuels
Plant/animal matter
Coal
Fossil fuel
Oil
Fossil fuel
Natural Gas
Fossil fuel
Nuclear
Uranium/plutonium
💡 Key Points:
Fossil Fuels (coal, oil, gas):
• Burned to release chemical energy
• Release CO₂ (greenhouse gas)
• Contribute to climate change
Nuclear:
• Uses nuclear fission
• No CO₂ during operation
• Produces radioactive waste
• Burned to release chemical energy
• Release CO₂ (greenhouse gas)
• Contribute to climate change
Nuclear:
• Uses nuclear fission
• No CO₂ during operation
• Produces radioactive waste
🎯 Resource Classification
How Power Stations Work
Most electricity generation follows the same basic process:
Most electricity generation follows the same basic process:
Fuel
(chemical energy)
→
(chemical energy)
Boiler
(heats water)
→
(heats water)
Turbine
(spins)
→
(spins)
Generator
(electricity)
(electricity)
Standard Power Stations:
In most power stations (fossil fuel, nuclear, geothermal, biofuel):
1. A fuel is burned (or nuclear reaction occurs)
2. Heat boils water to create high-pressure steam
3. Steam spins a turbine
4. Turbine is connected to a generator
5. Generator uses electromagnetic induction to produce electricity
1. A fuel is burned (or nuclear reaction occurs)
2. Heat boils water to create high-pressure steam
3. Steam spins a turbine
4. Turbine is connected to a generator
5. Generator uses electromagnetic induction to produce electricity
💡 Direct Generation Methods:
Some methods are more direct and don't need a boiler:
Wind & Hydroelectric:
• Moving wind or water spins the turbine directly
• No fuel burned, no steam needed
Solar Panels (Photovoltaic):
• Convert sunlight directly into electricity
• No moving parts at all.
Wind & Hydroelectric:
• Moving wind or water spins the turbine directly
• No fuel burned, no steam needed
Solar Panels (Photovoltaic):
• Convert sunlight directly into electricity
• No moving parts at all.
| Energy Source | Method | Advantages | Disadvantages |
|---|---|---|---|
| Fossil Fuels | Burn → Steam → Turbine | Reliable, high output | CO₂ emissions, will run out |
| Nuclear | Fission → Steam → Turbine | High output, no CO₂ | Radioactive waste, expensive |
| Wind | Wind → Turbine directly | No emissions, renewable | Weather-dependent, visual impact |
| Solar PV | Light → Electricity directly | No emissions, low maintenance | Weather-dependent, large area |
| Hydroelectric | Water → Turbine directly | Reliable, can store energy | Limited locations, ecosystem impact |
🎯 Power Station Quiz
Real Life Considerations:
• Energy security: Countries need reliable energy supplies
• Climate change: Moving away from fossil fuels to reduce CO₂
• Cost: Balancing setup costs vs running costs
• Location: Some resources only work in certain places
• Storage: Renewable energy needs storage for when sun/wind unavailable
• Energy security: Countries need reliable energy supplies
• Climate change: Moving away from fossil fuels to reduce CO₂
• Cost: Balancing setup costs vs running costs
• Location: Some resources only work in certain places
• Storage: Renewable energy needs storage for when sun/wind unavailable