At $$50\% $$ of full load, the armature current drawn by a $$d.c.$$ shunt motor is $$40$$ A when connected to a $$200$$ $$V$$ $$d.c.$$ mains. By decreasing the field flux, its speed is raised by $$20\% $$ this also causes a $$10\% $$ increase in load torque. Calculate the percentage change in field current. The armature resistance including the brushes is $$1$$ $$Ohm.$$ Neglect saturation and armature reaction.

A separately excited $$d.c.$$ motor has an armature resistance of $$0.5$$ $$ohm.$$ It runs off a $$250$$ $$V$$ $$d.c.$$ supply drawing an armature current of $$20$$ $$A$$ at $$1,500$$ $$rpm.$$ The torque developed for an armature current of $$10$$ $$A$$ will be __________ for the same field current.