Efficiency & Energy ResourcesEdexcel GCSE Physics: Revision notes

Efficiency compares the useful energy output of a device to the total energy put into it:

efficiency = useful energy transferred by the device ÷ total energy supplied to the device

• Efficiency has no units when expressed as a decimal (a value between 0 and 1), or can be given as a percentage by multiplying by 100.
• No device can be 100% efficient — some energy is always dissipated, usually to the thermal store of the surroundings.

Efficiency can be increased by reducing the amount of energy that is wastefully dissipated, for example:

• Reducing friction through lubrication of moving parts
• Improving thermal insulation to reduce unwanted thermal energy transfer to the surroundings
• Using materials or designs (e.g. streamlining) that reduce resistive forces

Since total energy supplied is fixed for a given process, reducing wasted energy means a greater proportion of the input energy is usefully transferred, raising efficiency.

Energy resources are grouped as non-renewable or renewable:

• Non-renewable resources will eventually run out, as they are used much faster than they can be replaced.
• Renewable resources are replenished naturally and will not run out, though supply can be less reliable (e.g. wind and solar depend on weather).

• Fossil fuels are currently the dominant global energy resource, mainly for electricity generation, heating and transport, but their use produces carbon dioxide emissions linked to climate change.
• Nuclear power provides a large, reliable supply of electricity without direct carbon dioxide emissions, but raises concerns over waste disposal and safety.
• Renewable resources (wind, hydroelectric, tidal, solar, bio-fuel) are increasingly used to generate electricity and reduce reliance on fossil fuels, though they often depend on location, weather and can be more expensive to set up.
• Over recent decades, there has been a general trend towards increasing use of renewable resources and a gradual decrease in reliance on fossil fuels, driven by concerns about climate change, pollution and the finite nature of fossil fuels.