Efficiency

The efficiency of a device is the **proportion** of the energy supplied that is **transferred** in **useful ways** in GCSE physics.

Energy efficiency is not just about heating homes. Everything that transfers energy **wastes** some of the energy as **heat **to the **surroundings**.

Energy can be **transferred** usefully, stored or dissipated.** It cannot be created or destroyed**.

In GCSE physics curriculum, you must know this **equation** in order to be able to work out efficiency:

*efficiency = useful energy output (x100) ÷ total energy input*

Sankey Diagrams

It looks like the one below which is for an filament lamp, sankey diagrams show** energy transformation**, therefore the energy efficiency is shown.

The **width** of each arrow depends on the **amount** of energy transferred to each element.

The energy transfer to light energy is the **useful **transfer, the rest is ‘**wasted**’.

Payback time

To be able to calculate the **payback time** you must know this **equation **in GCSE physics:

*payback time (years) = cost of insulation (£) ÷ annual saving (£)*

As we know homes lose energy so to reduce the energy loss the uninsulated homes need to be **insulated **which could be quite **expensive**

This means that it will **cost **you money in order to save money thus the equation helps you workout the in how many **years** you will be given back the money you spent on the insulation.

Payback time calculation helps us to work out the most **cost-effective** type of insulation.

End of this part! Lets continue in part II !!

Drafted by Gina (Physics)