Two pipes of inner diameter $$100mm$$ and outer diameter $$110mm$$ each are joined by flash butt welding using $$30V$$ power supply. At the interface, $$1mm$$ of material melts from each pipe which has a resistance of $$42$$ Ohms.If the unit melt energy is $$64.4$$ $$MJ/{m^3}$$, then time required for welding (in $$S$$) is

Aluminium strips of $$2mm$$ thickness are joined together by resistance spot welding process by applying an electric current $$6000$$$$A$$ for $$0.15sec$$. The heat required for melting aluminium is $$2.9J/m{m^3}.$$ The diameter and thickness of the weld nugget are found to be $$5$$ $$mm$$ and $$2.5mm$$ respectively. Assuming the electrical resistance to be $$75$$ micro-ohms, the percentage of total energy utilized in forming the weld nugget is

Which pair among the following solid state welding processes uses heat from an external source
$$P$$- Diffusion welding
$$Q$$- Friction welding
$$R$$- Ultrasonic welding
$$S$$- Forge welding

The $$DC$$ power source for arc welding has the characteristic $$3V + 1 = 240,$$ where $$V=$$ Voltage and $${\rm I}\,\, = $$ current in amp. For maximum arc power at the electrode, voltage should be set at