# Notes for P1b (OCR Gateway Science)

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• Created by: Alfiya
• Created on: 25-12-12 21:07

Keeping homes warm

Efficiency and payback time

Efficiency:

The efficiency of a device is the proportion of the energy supplied that is transferred in useful ways

- 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.

- 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

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.

Energy Transfer

Heat energy can be lost from homes in many different places but there are ways of reducing these losses.

There are three

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can u add questions on information will be much easier to retain information.

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Some great notes for many exam boards including OCR P1b and AQA P1 exam.

Nice and colour notes to explain heat transfer and Sankey diagrams.

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