The filament of an incandescent light bulb is made of tungsten which has a thermal coefficient of resistivity of α = 4.4 x 10-3 k-1. the filament is initially at room temperature, to = 293 k. when it is connected across a v = 140 volt power supply the filament quickly heats up to t = 2900 k at which time the current flowing through the filament is i = 0.95 amps.

The current when the filament at room temperature is 11.84 A.

Explanation:

Given that,

Thermal coefficient of resistivity

Initial temperature = 293 K

Voltage = 140 Volt

Final temperature = 2900 K

Current = 0.95 A

Suppose we find the numerical value of the current when the filament is at room temperature

So, We use the equation of resistance of a material changes with temperature

....(I)

Using ohm's law for value of resistance

Put the value of resistance in the equation (I)

Put the value into the formula

Hence, The current when the filament at room temperature is 11.84 A.

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