3.2 Energy and Work - Applications and Efficiency

When energy is transferred, some is always dissipated (wasted), usually as heat or sound. For example, a car engine is designed to transfer chemical energy (from fuel) into kinetic energy (movement), but a lot of energy is wasted as heat to the surroundings and noise.

Efficiency is a measure of how much of the total energy input is transferred into a useful energy output.

Efficiency = Useful Energy Output / Total Energy Input

You can also calculate it using power:

Efficiency = Useful Power Output / Total Power Input

Efficiency has no units. It can be given as a decimal (e.g., 0.60) or a percentage (e.g., 60%) by multiplying the decimal by 100.

Example: If a light bulb uses 100 J of electrical energy every second (100 W) and produces 20 J of light energy (20 W), its efficiency is:

Efficiency = 20 J / 100 J = 0.20, or 20%. The other 80 J (80 W) is wasted as heat.

We can increase efficiency by reducing wasted energy, for example, by using lubrication to reduce friction in an engine.

We use energy resources for transport, heating, and generating electricity. They can be split into two groups.

Renewable Resources

Renewable energy sources will not run out, or can be "renewed" at the same rate they are used. They are often weather-dependent and can be unreliable.

• Solar: Energy from the sun (using solar panels).
• Wind: Energy from the wind (using wind turbines).
• Hydroelectric: Energy from moving water in dams.
• Tidal: Energy from the flow of the tides.
• Geothermal: Energy from heat inside the Earth.
• Biofuels: Fuels made from plant matter or animal waste.

Non-Renewable Resources

Non-renewable energy sources will one day run out. They were formed over millions of years and we are using them much faster than they can be replaced. They are reliable (not weather-dependent) but release greenhouse gases.

• Fossil Fuels: Coal, oil, and natural gas. These are burned to release their chemical energy.
• Nuclear: Energy from nuclear fission, using fuels like uranium and plutonium.

Most electricity generation works in the same way:

1. Fuel → 2. Boiler → 3. Turbine → 4. Generator

In most power stations (fossil fuel, nuclear, geothermal, biofuel), a fuel is used to heat water and create steam. This high-pressure steam spins a turbine, which is connected to a generator. The generator uses electromagnetic induction to produce electricity.

Other methods are more direct:

• Wind and Hydroelectric: The moving wind or water spins the turbine directly, with no boiler needed.
• Solar Panels (PV): These convert sunlight directly into electricity with no moving parts.