# 4 problems involving resistance, tungsten filaments, current, emf

See attached file for problems of resistance, tungsten filaments, current, emf.

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#### Solution Preview

1.) because thermal coeff. of electrical resistivity of tungsten (a):

a = 0.0046 /degree centigrade

at 20 degree centigrade:

V = i*R

V = 100 volt

i = 6.0 amp.

R = (3 + ri) ohm

where ri is the internal resistance of battery.

=> 100 = 6 * ( 3 + ri)

=> ri = (50/3) - 3 = 13.67 ohm

Now at 2000 deg C:

R2000 = R20 * {1 + a * (2000 -20)}

= 3 * (1 + 0.0046 * 1980) = 30.32 ohm

therefore at 2000 deg C:

i = V /( ri + R2000) = 100/(13.67 + 30.32) = 2.27 A Ans

P = i^2 *R = (2.27)^2 ...

#### Solution Summary

With very detailed computations, the problems are solved.

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