The resistance of a coil of copper wire is $3.35 \Omega$ at $0{ }^{\circ} \mathrm{C}$. What is its resistance at $50^{\circ} \mathrm{C}$ ? For copper, $\alpha=4.3 \times 10^{-3}{ }^{\circ} \mathrm{C}^{-1}$
$$
R=R_{0}+\alpha R_{0}\left(T-T_{0}\right)=3.35 \Omega+\left(4.3 \times 10^{-3}{ }^{\circ} \mathrm{C}^{-1}\right)(3.35 \Omega)\left(50^{\circ} \mathrm{C}\right)=4.1 \Omega
$$