Two steel sheets of thickness one mm arc welded by resistance projection welding technique. A current of 30,000 A for 0.005 second is made to flow. The effective resistance of joint can be taken as 100 micro ohms. The joint can be considered as a cylinder of diameter 5 mm and height 1.5 mm. The density of steel is 0.00786 gm/mm3. The heat needed for welding steel is 10 /mm3. Calculate the efficiency of welding.