Wasted Energy (AQA GCSE Physics): Revision Note

Wasted Energy

• In practice, most systems are not closed

• When energy transfers occur that are not useful, these are described as energy being dissipated to the surroundings

  • Dissipated means the energy is spread out into the surroundings and stored in a less useful way

  • Energy is never destroyed, so it is wrong to say it is 'used up' or 'destroyed'

  • This is considered to be wasted energy

• These less useful energy transfers often involve heating, light and sound

• When energy is transferred to the thermal stores of the objects, the temperature of the objects increases

  • The particles that make up the objects vibrate more; hence, the transfer pathway is by heating (of the particles)

• Visible light is electromagnetic radiation

  • Therefore, when light is produced, energy is transferred by radiation

• When sound is produced, energy is carried away by waves (mechanically) as air particles vibrate

  • The vibrating air particles then pass energy to the thermal store of the surroundings, so the energy is dissipated

• Useful energy can be defined as:

The energy that is transferred from store to store and used for an intended purpose

• Wasted energy can be defined as:

The energy that is not useful for the intended purpose and is dissipated to the surroundings

Reducing Energy Loss

• Mechanical processes can become wasteful when they cause a rise in temperature

• These processes often involve friction

  • When friction acts, it has the effect of transferring energy from the kinetic store by heating to the objects and the surroundings

  • This energy cannot be used in a useful way, therefore it is called wasted energy

  • Energy that is transferred to the surroundings is said to be dissipated (spread out) to the surroundings

Lubrication

• Friction is a major cause of wasted energy in machines

• For example, the gears on a bike can become hot if the rider has been cycling for a long time

  • Energy is wasted as it is transferred from the kinetic energy store of the bike to the thermal energy store of the gears and the chain

  • This friction makes them become hot and transfers energy by heating to the thermal energy store of the surrounding air

• This wasted energy can be reduced if the amount of friction can be reduced

  • This can be achieved by lubricating the parts that rub together

    • Less work is done against friction, so less energy is transferred to the thermal store of the parts and the surroundings

    • A greater proportion of the input energy is transferred usefully, so the efficiency increases

Lubrication helps reduce friction in the parts of a cycle

Insulation

• In many situations, the energy transferred by heating is wanted. For example:

  • When heating a home

  • When boiling a kettle

• If this energy can be prevented from dissipating, then less energy will be needed to replace the wasted energy

  • This can be achieved by surrounding the appliance with insulation

• The effectiveness of insulation depends upon:

  • How well the insulation conducts heat

  • How thick the insulation is