The filament of a lightbulb has a resistance of r0=12ω at 20 ∘c and 140 ω when hot
a.) calculate the temperature of the filament when it is hot, and take into account the change in length and area of the filament due to thermal expansion (assume tungsten for which the thermal expansion coefficient is ≈5.5×10−6(c∘)−1). use the equation rhot=rho0(1+α(t− assuming an average temperature coefficient of resistivity α=0.0045(c∘)−1.
i found this to be 2400 degrees c.
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b.) in this temperature range, what is the percentage change in resistance due to thermal expansion?
c.) what is the percentage change in resistance due solely to the change in rho?