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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