Question

A cylindrical tungsten filament 13.0 cm long with a diameter of 1.00 mm is to be used in a machine for which the temperature will range from room temperature (20 ∘C) up to 120 ∘C. It will carry a current of 12.5 A at all temperatures ( Resistivity of tungsten at 20 ∘C is 5.25×10−8Ω⋅m , the temperature coefficient of resistivity at 20 ∘C is 0.0045 ∘C−1 )

What will be the maximum electric field in this filament?

What will be its resistance with that field?

What will be the maximum potential drop over the full length of the filament?

Answer 1

Ansco! 9iven data ig Rength &tungsen bilament I3Cm -0.13 m cImm = r= 0.5mm A) By cuing ohms law J oE J = E P E = -LP A At aoc, veslstvig 18 5.25xi(+(0.04)(DO-16) P = fo (td (T-T,) 5 35x5.5 .25X1O (0.0045) (126-26) 7.61X 10 m Area ot cylndei 18 62 A 3u (0.5X1o- o165 , mazimum elecric bield iS (7.61x10) (12.5 A) PI E = A o.T85X10m 1.21 NJC RIsistance cDith fiuld (7.61xi08 (0.13 m) PL 0.785x166 m |-26x10 = 0.0126 (12.5A) (0.0126 -2) max=IR Scanned with CS CamScanner O.158 V