A 3-phase star-connected electric furnace has a resistance of 20 Ω per phase and is supplied by a balanced 400 V, 50 Hz line-to-line AC source. The total heat energy produced in 30 minutes is:

Copper (density = 8960 kg/m3, ECE = 3.29 × 10-7 kg/C) is electroplated on an area of 0.2 m2 to a thickness of 20 μm. If a steady current of 50 A is passed, the time required is approximately:

In a resistance welding operation, a current of 5000 A flows through a joint resistance of 150 μΩ for a duration of 0.5 s. The total heat energy generated at the joint is: