SITEMAP   School-college Physics Notes: Electricity 1.2 Usefulness of electricity

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Electricity in the home: 1.2 The usefulness of electrical appliances in the home

(We depend a lot on our electricity supply e.g heating, cooking, lighting, entertainment, radio, TV, computers and cleaning)

Doc Brown's Physics exam study revision notes: There are various sections to work through, after 1 they can be read and studied in any order. Why are electrical devices so useful?

1.2 The usefulness of electrical appliances in the home

• Appreciate that we often use electrical appliances because they transfer energy into other useful at the flick of a switch ie very convenient!

• Energy is transferred because the electric charge does work against the circuit resistances) - remember: work done = energy transferred.

• Electrical appliances are designed to transfer to do useful work in a circuit when the current flows through the components of e.g. heating element of a fire or kettle (electrical energy supply to a thermal energy store), motion in a food mixer (electrical to a kinetic energy store) etc.

• Don't forget that no appliance is perfect (100% efficient), because there are always energy losses.

• The greater the current flowing, the greater the energy transferred to the thermal energy stores of the components and of course, wasted heat energy to the surroundings.

• Just think of all the devices-appliances that run off electricity in the home.

• Examples of energy conversions:

• (Most involve transferring mains/battery supply electrical energy into some other useful form of energy using an appliance of some sort, but remember, most energy transfers here involve wasted heat energy increasing the thermal energy store of the surroundings)

• Examples of such energy transfers include ...

• Light bulbs - mains electricity ==> heat and light

• Torch light - chemical energy store of battery ==> electrical energy ==> heat and light

• TV - mains electrical energy ==> light and sound and lots of wasted heat

• Refrigerator - mains electrical energy ==> kinetic energy of heat pump ==> thermal energy store of surroundings (dissipated heat)

• Hair dryer - mains electrical energy ==> kinetic energy store of the blower fan and thermal energy from the heating elements - all energy eventually increases the thermal energy store of the surroundings

• CD player - mains/battery electrical energy ==> kinetic energy and sound

• Radio - mains/battery electrical energy ==> sound

• Oven - mains electrical energy to thermal energy (via conduction, convection or radiation)

• Computer or mobile phone charger and use - mains electrical energy ==> chemical energy store of battery ==> light and sound when using your phone

• Electric toothbrush - mains electricity ==> chemical energy store of battery ==> electrical energy powering a small motor ==> kinetic energy store of brushes

• Hoover or food mixer - electrical energy ==> kinetic energy

• Microwave oven - electrical energy ==> EM microwave radiation and kinetic energy

• Lots of other stuff working off electricity ... Iron, immersion heater, telephone, internet etc. etc.!

• Think of the importance of these devices-appliances in your life - music/TV on demand, food safely stored in the fridge, light to read by in the evening

• Try to imagine life without your domestic electricity and think how wonderful 240V is!

• Quite simply the convenience and usefulness of mains electricity to our way of life and standard of living is incalculable, so don't waste it!

• Electrical appliances can be low or high power - convenient for the energy needs required to power most things in the home.

• Think of all those everyday tasks now done more conveniently with electrical appliances, saving your time and energy.

• Even with lighting, electric bulbs are rather better and safer than oil/gas lamps or candles!

• Powerful electrical machines in industry are easily run from mains electricity and can do jobs far more quickly than manual labour.

• This has allowed the efficiency of industrial production to be considerably increased.

• Steam power replaced people and steam replaced by electrical power - the power aspect of the industrial revolution!

• Lifts require a powerful electric motor and think of the hard work you do in climbing several flights of stairs without a lift! (but regular exercise is good for you)

 hair dryer toaster microwave cooker a 'retro' style radio food-mixer lamp laptop computer immersion heater - hot water tank The hot water radiator needs an .... electric motor to pump the hot water to it
• You should be able to use their skills, knowledge and understanding to:

• Be able to compare the advantages and disadvantages of using different electrical appliances for a particular application,

• You will be required to compare different electrical appliances, using data provided.

• This may involve energy use and cost effectiveness and also to consider the implications of instances when electricity is not available.

• For developing countries where infra-structure lacks a reliable mains electricity supply, battery operated devices can be used and even clockwork radios have been designed.

• However, batteries are costly despite being a convenient supply of stored chemical energy which converts to electrical energy on demand. They also don't last very long!

• In the case of a clockwork powered radio, when the radio is 'wound up' the energy is stored as elastic potential energy and again released as needed to listen to the radio, for free! This completely avoids the need for costly batteries and their safe disposal to avoid pollution.

• Without mains electricity, communities in developing countries cannot have the same standard of material living.

• You should also be aware that some energy is 'wasted' or 'dissipated' because electrical appliances are never 100% efficient when switched on!

• The waste energy usually ends up increasing the thermal energy store of the component or surroundings e.g. from friction of moving parts or heat from overheated circuits.

• In fact, if a resistor increases in temperature, its resistance increases and even more energy is lost.

• Also, the greater the current flow, the greater the thermal energy losses (see the National Grid system for a 'big' example!).

• Despite the wasted energy in many appliances, there are obvious instances where we want the electrical energy to end up as heat.

• Electrical heaters is the most obvious example - you use a high resistance a coil of wire to act as a heating element in an appliance e.g. electric fire, toaster etc.

• In both these cases, the resistor becomes so hot it glows red - electrical energy store of circuit ==> thermal energy store of resistor ==> infrared radiation ==> thermal energy store of food to cook it or to warm up the surroundings etc.

• The thin metal filaments of filament bulbs need to become very hot to emit useful light.

• rely on an 'overheating' effect to protect an appliance and ourselves from electrocution.

INDEX of ELECTRICITY Notes 1. Electricity in the home

Keywords, phrases and learning objectives for useful appliances in the home

Be able to describe and explain the usefulness electrical appliances in the home e.g. how much we depend on electricity for uses like heating, cooking, lighting, entertainment radio TV, computers and cleaning and washing machines.

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INDEX of ELECTRICITY Notes 1. Electricity in the home

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