A coil of platinum wire has a resistance of 100.0 Ω at 20 °C…

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A coil of platinum wire has a resistance of $100.0\ \Omega$ at $20\ ^\circ$ C. Its temperature coefficient is $3.9 \times 10^{-3}$ per $^\circ$ C. The coil is put in a hot bath and reads $128.5\ \Omega$ . What is the temperature of the bath?

Need a reminder? The key ideaShow

For a metal, $R_T = R_0[1 + \alpha(T - T_0)]$ , with $T_0 = 20\ ^\circ\text{C}$ . In a colour code, the first two bands give digits, the third gives the power of ten, and the last gives the tolerance: gold $\pm 5\ \%$ , silver $\pm 10\ \%$ , none $\pm 20\ \%$ .

The worked solution

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Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

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