A 4 pole dc generator has 1200 armature conductors and generates 250 V on open circuit running at a speed of 500 rpm. The diameter of the pole shoe circle is 0.35 m and the ration of pole arc to pole pitch is 0.7 while the length of the shoe is 0.2 m. Find the mean flux density in Tesla in the air gap. Assume lap winding in armature