Q$\mathrm{.}4)$ A resistance spot welding operation is performed on two pieces of $1\mathrm{.}5$ mm thick sheet steel using $12000$ A for a $0\mathrm{.}2$ sec duration.. The electrodes are $7$ mm in diameter at the contacting surfaces, resistance is assumed to be $0\mathrm{.}0001$ ohm, and the resulting weld nugget is a sphere of a $6$ mm in diameter. The unit melting energy for the metal $U=12\mathrm{.}0\frac{J}{m}m3.$ What portion of the heat generated was used to form the weld nugget and what portion was dissipated in to the work metal, electrodes and surrounding air.