Page 38 - Electrician - TT (Volume 1)
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ELECTRICIAN - CITS



           Conductors, insulators and semi-conductors

           Conductor: It is a substance which has a large No. of free electrons. Conductors allow the flow of electric current.
           The number of valence electrons of a conductor is less than four. Most metals are good conductors. Eg; copper,
           Al etc. (Fig 4)


              Fig 4

















           Insulators: Which has practically no free electron at ordinary temperature.therefore, an insulator does not conduct
           electric current. No. of valence electron in the insulator is more than four.
           Semi-conductors: Characteristics of semiconductor is in between conductor and insulator.it has very few free
           electrons at room temperature. consequently’ a semiconductor practically conducts no current. The number of
           Valence electrons in the semiconductor is four. (Fig 5)


              Fig 5















           Eg; silicon and germanium

           Electrical circuit
           Simple electrical circuit consist of
           An Energy Source (Cell)
           Conductor
           A load (Resistor)
           A control device (Switch)

           Definitions of electrical terms
           Current: The flow of electrons in one direction along any path or around any circuit is called electric current. Its
           symbol is I and its unit s ampere (A). The instrument which is used to measure current is called ‘AMMETER’,
           which is always connected in series with the circuit.
           Electro Motive Force (EMF): The force which causes current to flow in the circuit is called EMF. Its symbol is E
           and is measured in volts (V) The EMF of an electrical source may be referred as its voltage.
           EMF=voltage at the terminal of the source of   supply + voltage drop in the supply source
               EMF=VT+IR



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                                    CITS : Power - Electrician & Wireman - Lesson 5 - 12
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