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Question

The temperature of a sample of copper is raised while a sample of silver is maintained at 20°C. At what temperature will the resistivity of the copper be two times that of the silver?

Answer 1

I only can give you the rough approach.
We look an the resistivity of copper and silver at 20 degrees Celsius
r (copper, 20C) = 0.017 (microOhm*m)
r (silver, 20C) = 0.016 (microOhm*m)

Then we assume that the resistivity of copper changes as the following:
r (copper, T) = r (copper, 20C)(1 + k(T - 20C)),
in all range of the increasing temperatures. We have such law with rather good accuracy in the range ( 0 C - 100 C).
The k is the koefficient well measured for many metals, and it equals k = 0.0043 for copper.
We have to find then temperature, at which
0.032 (microOhm*m) = 0.017 (microOhm*m)(1 + 0.0043*(T - 20C).
and
32/17 = 1 + 0.0043*(T - 20C), and
15/17 = 0.0043(T - 20C), and
T - 20C = 15/(17*0.0043) = 205 degrees,
So T = 225 C

This is in the assumption of linearity of temperature dependence of resistivity up to the value of 225 degrees Celsius

Answer 2

You didn't provide enough data for this problem, you have to know the temperature coefficients of specific electrical resistance both for copper and for silver.