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ELECTRICAL MEASURING INSTRUMENTS For the detection or measurement of electric current, potential difference, and resistance certain instruments have been devised viz. The galvanometer for the detection of small currents measurements of small currents of the order of micro amperes or mili amperes the voltmeter or potentiometer for the measurement of potential difference (and voltage) between two points of a circuit are the EMF of a source the ammeter for the measurement of large currents the wheatstone bridge the meter Bridge the post office box and the ohmmeter for the measurement of resistance. THE MOVING COIL GALVANOMETER The moving coil galvanometer is a basic electrical instrument it is used for the detection (and Measurement) of small currents. Its underlying principle is the fact that when a current flows in a rectangular coil placed in a magnetic field it experiences a magnetic torque. If it is free to rotate under a controlling torque, it rotates through an angle proportional t...
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METALLURGY OF COPPER

Copper occurs both in free as well as in combined states.In combined state,it occurs mainly as the sulphide and oxide ores.The chief ores of copper are copper pyrite or chaleopyrite (CuFeS2), chalocite (Cu2S) and malachite [Cu(OH)2] and azurite [2CuCO3 Cu(OH)2 blue.

Extraction 

Copper is mostly extracted from sulphide ores which contain about 6% Cu.The sulphide ore is first roasted (i.e., heated strongly in a current of air) on the hearth of a large flat furnace whereby the following changes occur.

(i) Large amount of sulphur burns to sulphur dioxide (SO2).

(ii) Iron present oxidizes to ferrous oxide (FeO) 

(iii) Copper changes into cuprous sulphide (Cu2S)

2CuFeS2 + 4O2 -----------> Cu2S + 2FeO + 3SO2

The roasted material is then mixed with sand to remove iron as ferrous silicate a slag which floats on the surface of the molten matte of copper.The liquid copper matte containing cuprous sulphide with some unreacted ferrous sulphide (FeS) and silica oxidized in a Bessemer converter by blowing air through.FeS is oxidized to FeO and SO2 Ferrous oxide reacts with sand to give ferrous silicate and the blast of air converts Cu2S partly into Cu2O which reacts with the remaining Cu2S to give metallic copper in its molten state.

2FeS +3O2 ----------> 2FeO +2SO2

FeO + SiO2 -------------> FeSiO3

2CuS + 3O2 -----------> 2Cu2O + 2SO2

2CuO + Cu2S -------------> 6Cu +SO2

The copper thus produced is called blister copper because as it solidifies hidden sulphur dioxide gas and excapes producing blisters on its surface.It is about 99%  pure.The blister copper contains impurities mainly iron but small amount arsenic,Zinc,lead,silver and gold may also be present.As such, the copper is not suitable particularly for electrical work so it is thus refined 

Refining of Copper:

Copper is refined by electrolysis in which blocks of blister copper are as anodes and thin sheets of pure copper as cathodes.The cathode plates or sheets are coated with graphite in order to remove depositing copper easily.The electrolyte is copper sulphate acidified with sulphuric acid.The current of 1.3 volts is used for electrolysis soluble and fall to the bottom of the cell as a sludge or anode mud.The chemical reactions which occur are give as under

Cu -------------------> Cu ++     +      2e (At anode)
Cu2+          +           2e--------------------> Cu (At cathode)

      

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