A 4-pole, 50 Hz scharg motor, running at no-load, gives minimum and maximum speeds of 500 and 2500 r.p.m. respectively, for brush separation of 180 electrical degree (i.e. one pole pitch). Find the brush separation in electrical and mechanical degrees for no-load speeds of (a) 1000 r.p.m.and (b)1800 r.p.m.