$5.(8$ pts$)$ At time t$,$ the $4$ pole machine stator has current, ia $=20$ A$,$ ib $=-10$A$,$ ic $=-10$ A$,$ the air

gap length is $2$ mm$,$ each winding is $500$ turns, calculate

a$)(3$pt$)$ magnetic field in each phase as a function of $,($Ba$,$ Bb$,$ and Bc$)$

b$)(3$ pts$)$ Magnetic filed of the stator a function of $($Bs$)$

c$)(1$pt$)$ Bs at $=60$ deg

d$)(1$ pt$)$ The rotation speed of the magnetic filed in rpm $($f $=60$ Hz$)$