Energy Transfers

Energy cannot be created or destroyed. This is better known as the law of conservation of energy.
Despite not being able to create or destroy energy, it can be transferred or transformed from one form into another.
For instance, in a torch, chemical energy stored in the batteries is transformed into light and thermal energy.

Mechanical work: A force acting on an object moves the object, transferring energy in the process. For instance, pushing a trolley imparts kinetic energy to it.
Electrical work: Energy can be transferred via an electric current, such as when a fan uses electricity to generate wind.
Heating: Energy can be transferred from a hotter object to a cooler one, increasing the cooler object’s internal energy.
Radiation: Energy can be transferred via light or other electromagnetic waves, such as the energy received from the sun.

Efficiency measures how much of the input energy is usefully transferred and not wasted. The higher the percentage, the more efficient the energy transfer.
Efficiency can be calculated using the formula: Efficiency = (Useful energy output / Total energy input) × 100%.
All energy transfers are to some extent inefficient as some energy is invariably ‘wasted’, most commonly as thermal energy or heat.
Efficiency improvements are vital for sustainable energy use, reducing the amount of energy required for a given task, and limiting environmental damage.

For example, in a car, chemical energy in petrol is transformed into kinetic energy of the moving vehicle, but also non-useful forms such as sound and heat.
In a coal-burning power station, energy transfers occur successively: chemical (coal) to thermal (heat) to kinetic (steam) to mechanical (turbine) to electrical (generator).
Many appliances including TVs, computers and fridges use electrical energy and convert it into other forms - thermal, light, sound etc.
Knowledge about these practical applications of energy transfer is crucial when answering real-life scenario based questions.
The key is to identify all instances where energy is usefully converted or lost as waste energy.