Physics 1.2 JaskiratK

Energy & Efficiency

Appliances transfer energy but not all the energy is transferred in useful ways.

Energy Forms

Types Of Energy:

Kinetic (Movement) The energy in moving objects.

Electrical Energy Energy in moving charges or static electric charges.

Heat (Thermal) Also called thermal energy.

Elastic Potential Stored energy in stretched or squashed objects.

Light Energy Also called radiant energy.

Nuclear Energy Stored in the nuclei of atoms.

Gravitational Potential (GPE) Stored energy in raised objects.

Internal Energy Contained in Thermodynamic system

Chemical Energy Stored energy in fuel, foods and batteries.

Stain Energy Released when atoms in a molecule rearrange themselves in a chemical reaction

Sound Energy Energy released by vibrating objects.

Magnetic Energy Energy in magnets and electro-magnets

Description:

Physics - P1.2

Different forms of energy can be transferred from one form to another. Energy transfer diagrams show each form of energy - whether it is stored or not - and the processes taking place as energy is transferred.

Energy Transfers & Diagrams

The next diagram shows the energy transfer diagram for the useful energy transfer in an

electric lamp. You can see that the electric lamp transfers or converts electrical energy into light

energy.

The energy transfer diagram below shows the useful energy transfer in a car engine. You can see that a kinetic energy car engine transfers chemical energy, which is stored in the fuel,

into  in the engine and wheels.

Process Of Using Chemical Energy: Process Of Using Electrical Energy:

Note that these energy transfer diagrams only show the useful energy transfers. However, car engines are also noisy and hot, and electric lamps also give out heat energy.

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Sankey Diagrams

Sankey Diagram Showing The Energy Transfer In A Electric Fridge.

The efficiency of a device can be calculated using this equation:Efficiency = Using Energy Output ÷ Useful Energy Input The efficiency of the electric fire in the example is 90 ÷ 100 = 0.9Note that the efficiency of a device will always be less than 1.

Physics - P1.2

Sankey diagrams summarise all the energy transfers taking place in a process. The thicker the line or arrow, the greater the amount of energy involved.This Sankey diagram for an electric lamp shows that most of the electrical energy is transferred as heat rather than light.

Energy can be transferred usefully, stored or dissipated. It cannot be created or destroyed. Notice that 100 J of electrical energy is supplied to the lamp. Of this, 10 J is transferred to the surroundings as light energy. The remainder, 90 J (100 J – 10 J) is transferred to the surroundings as heat energy.The energy transfer to light energy is the useful transfer. The rest is ‘wasted’: it is eventually transferred to the surroundings, making them warmer. This ‘wasted’ energy eventually becomes so spread out that it becomes less useful.

EfficiencyOrdinary electric lamps contain a thin metal filament

that glows when electricity passes through it. However, most of the electrical energy is transferred

as heat energy instead of light energy.

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This Is The Sankey Diagram For A Typical Filament Lamp:

Modern energy-saving lamps and LEDs (light-emitting diodes) work in a different way. They transfer a greater

proportion of electrical energy as light energy

This Is The Sankey Diagram For A Energy Saving Lamp:

From the diagram, you can see that much less electrical energy is transferred, or 'wasted', as heat energy from the energy-saving lamp. It's more efficient than the filament lamp.

Calculating Efficiency:

The efficiency of devices can be calculated.• Efficiency = Useful Energy Out ÷ Total Energy In (For A Decimal Efficiency)• Efficiency = (Useful Energy Out ÷ Total Energy In) x 100 (For A Percentage Efficiency)

The efficiency of a device will always be less than 100 per cent. Occasionally the power is shown in W instead of the energy in J. The equations are the same – just substitute power for energy: • Efficiency = Useful Energy Out ÷ Total Energy In (For A Decimal Efficiency)• Efficiency = (Useful Energy Out ÷ Total Energy In) x 100 (For A Percentage Efficiency)

Efficiency:The efficiency of a device is the proportion of the energy supplied that is transferred in useful ways. You should be able to calculate the efficiency of a device as a decimal or as a percentage.

Energy CANNOT be created or destroyed. It can only be transferred from one form to another, or moved. Energy that is ‘wasted’, like the light energy from a glowing electric fire, does not appear. Instead, it is transferred into the surroundings and spread out so much that it becomes very difficult to do anything useful with it.

Payback Time:Home owners may install double glazing or extra insulation to reduce heat energy losses and so save money. However, these energy-saving solutions cost money to buy and install. The payback time of an energy-saving solution is a measure of how cost-effective it is. Here is the equation to calculate payback time:Payback Time (Years) = Cost Of Installation (£) ÷ Savings Per Year In Fuel Costs (£)The payback time will be shortest if the cost of installation is low compared to the savings made each year.

Payback Time

Example:The double-glazing for a house cost £3,000 but saves £150 per year in fuel costs.What is the payback time?

Payback Time = £3,000 (Cost Of Installation) ÷ £150 (Savings Per Year In Fuel Costs)Payback Time = 3,000 ÷ 150Payback Time = 20 Years

Physics - P1.2