The conductivity of tungsten at room temperature, ? = 1.8 ? 10 7 (A/m 2 )/(V/m),

Question

The conductivity of tungsten at room temperature, ? = 1.8 ? 107 (A/m2)/(V/m), is significantly smaller than that of copper. At the very high temperature of a glowing light-bulb filament (nearly 3000 degrees Kelvin!), the conductivity of tungsten is 18 times smaller than it is at room temperature. The tungsten filament of one of your round bulbs has a radius of about 0.015 mm. Calculate the electric field required to drive 0.40 amperes of current through the glowing bulb and show that it is huge compared to the field in the connecting copper wires.
_______________ V/m

Explanation / Answer

conductivity = 1.8*10^7 / 18 = 10^6

10^6 * 4* pi* (0.015*10^-3)^2 = E * 0.4,

E = 7.0465*10^-3 V/m

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