Answer :
Explanation:
At room temperature, resistivity of tungsten is [tex]5.6 \times 10^{-8}[/tex] and the resistivity of aluminium is [tex]2.8 \times 10^{-8}[/tex].
Temperature coefficient of aluminium ([tex]\alpha[/tex]) = [tex]3.9 \times 10^{-3}[/tex]
[tex]R_{a} = 3R_{c} = 5.1 \times 10^{-8} \ohm m[/tex]
and, [tex]R_{a} = R_{o}(1 + \alpha \times \Delta T)[/tex]
= [tex]2.82 \times 10^{-8} (1 + 3.9 \times 10^{-8} \times \Delta T)[/tex]
[tex]\Delta T = 207.3^{o}C[/tex]
T = [tex](207.3 + 20)^{o}C[/tex]
= [tex]227.3^{o}C[/tex]
So, at [tex]227.3^{o}C[/tex] aluminium has resistivity which is three times the resistivity of tungsten at room temperature.