2019/2020 THIRD TERM BASIC TECHNOLOGY FOR JUNIOR SECONDARY SCHOOL 2 (LESSON 1)

INTRODUCTION TO ENERGY-BASED TECHNOLOGY APPLIANCES 
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Electrical energy based appliances are those appliances we use in our homes, which are operated by electrical energy that passed through them, into other forms of energy such as heat, sound, and mechanical. Examples of electrical energy based appliances include the electric pressing iron, electric stove, immersion heater, electric kettle, water heater, electric soldering iron and the bread toaster. All these appliances convert electrical energy into heat energy when they are in operation. The input energy is electricity and the output energy is heat. A heating element, which becomes hot when current passes through it is fitted into each of the appliances. It is here that the conversion of electrical energy into heat energy takes place. The element is made of material with high resistance and so cannot melt easily

ELECTRICAL ENERGY-BASED APPLIANCES  (PART ONE) 
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1) Operation Of Pressing Iron: The basic principle of the appliance is that a heating element is built into it. As current flows through the circuit, the immense electrical energy used to overcome the high resistance is turned into heat energy and the heat thus produced is used in ironing. The electric iron is made up of the following parts:

a) A nichrome element wound on mica former.
b) Two heavy stainless steel plates in between which the element is fixed. The weight of the steel plates applying pressure which coupled with the heat from the element, soothens the clothes being ironed.
c) An asbestos pad, a poor conductor of heat, which is fitted to the upper steel plate to minimize the upward flow of heat from the element.
d) Mica plates which insulate the steel plates from electricity but conducts the heat from the elements to the lower steel plate for ironing.
e) A bimetallic thermostat which controls the extent to which the plates are heated.

The temperature produced by such irons varies between 121 degree celsius and 204 degree celsius. The lower temperature range is used for ironing synthetic materials like nylon, terrylene and so on, while the higher range of temperature is used for pressing cotton materials. 

2) Operation Of An Electric Kettle: An electric kettle is made up of the following:

a) A chrome-plated aluminum or copper body.
b) A nichrome element encased in a metal tube and insulated with a refractory material such as magnesia.

The tube must be watertight to avoid water leaking into the element.

When the element is heated, the magnesia insulation conducts the heat to the metal tube which is in contact with the water to be heated.

3) Operations Of An Electric Cooker: A modern electric cooker has several cooking points so that several items can be cooked at the same time. Each cooking point consists of a steel plate in which two nichrome elements spiral shape are fixed. The spiral shape of the elements makes it possible for a greater length of the element to be contained in a small space. 
The elements are encased in magnesia to insulate them from the steel plate. When the electric circuit is switched on, the element heats the metal disc to cooking temperature.

4) Water Heater (Free Outlet Type): There are various types of water heater such as free outlet, pressure type and cistern types. They operate on the basic principle of electric energy converted into heat and by conduction, cold water is heated. The main differences are:
a) The free outlet type supplies limited hot water by the inrush of cold water to displace the heated quantity at turning the only tap. Therefore it is fit for bathrooms with single tub.
b) The pressure type has an advantage of its ability to supply many hot water outlet points since many taps can be fitted on its outlet pipe but will always depend on the supply mains pressure.
c) An example of the cistern type is the cylindrical tank found in bathrooms. Like the electric kettle, the ceramic or metal tank contain nichrome elements insulated with magnesia and enclosed in a metal tube. Water heated by the immersion of the element, rises up in the tank thereby forcing the topmost hot water to flow freely outward.

Please, do the activity below (5 Marks)

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