PROBLEM
– 01
The filament of a 220 V metal-filament lamp is to
be constructed from a wire having a diameter of 0.02 mm and a resistivity at 20
degree centigrade of 5 µΏ-cm. If α = 0.005 per degree centigrade, what length
of filament is necessary if the lamp is to dissipate 100 watts at a filament
temperature of 2000 degree centigrade.
PROBLEM
– 02
Find
the current flowing at the instant of switching on a 40 W lamp filament on to a
220 V circuit, if the filament temperature at normal operating condition is
2800 degree centigrade. Resistance temperature coefficient of the filament at
room temperature of 20 degree centigrade = 0.005 per degree centigrade.
PROBLEM
– 03
A copper conductor has
its specific resistance of 1.6 x 10^-6 Ώ-cm at 0 degree centigrade and a
resistance temperature coefficient 39.3 x 10^-4 per degree centigrade at 20
degree centigrade. Find (i) the specific resistance (ii) the
resistance-temperature coefficient at 80 degree centigrade.
PROBLEM
– 04
The resistance
temperature co-efficient for a certain copper wire is 0.004 and for carbon
filament it is 0.0003. How many ohms of carbon filament is series with a 80 ohm
copper wire will make the total combined resistance invariant with temperature.
PROBLEM
– 05
Two
conductors one of copper and other of Iron are connected in parallel. At 20
degree centigrade, they carry equal currents.
If
the temperature is raised to 180 degree centigrade, what is the proportion of
the total current will each conductor carry?
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