Saturday, January 5, 2013

Some Effect of Heating Effect of Currents

The wires supplying current to an electric lamp are not practically heated while that of the filament of lamp becomes white hot. Wire has very less resistance but filament has higher resistance. Heating is proportional to R.
Nichrome wire (alloy of Ni and Cr): it has high melting point and high value of specific resistance.

            ii. It can be easily drawn
            iii. It is not oxidized easily when heated in air

Resistance of high electric power instruments is smaller than that of low electric power.

Fuse wire is generally prepared by tin-lead alloy. It should have high resistivity, low melting point and of suitable current rating. Fuse wire is used in series with electrical installation.

Efficiency of an electric device (η)

                                    η = output power/input power

      For electric motor,   η = output mechanical power/input electric power, input electric power =output mechanical power + power lost in heat.

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