A high-power fiber laser cutting system consumes a total electrical energy of 7.50×107 J7.50 \times 10^7\text{ J}7.50×107 J during a continuous metal-cutting operation. Of this energy, 4.95×107 J4.95 \times 10^7\text{ J}4.95×107 J is usefully converted into the electromagnetic radiation of the laser beam directed at the metal workpiece.
Calculate the efficiency of the laser cutting system as a proportion.
The electrical power consumption rating of the laser system is 12.5 kW12.5\text{ kW}12.5 kW. Calculate the time taken for the laser system to consume the total 7.50×107 J7.50 \times 10^7\text{ J}7.50×107 J of electrical energy. State the unit.