study the ac circuit at the right. R $=1000$ ohms, C $=1$uF$,$ and L $=900$mH$.$ The maximum voltage from the power source is $10$V$.$ This feed into the transformer with $90$ turns in the primary and $180$ turns in the secondary$.$ with the switch in position A$,$ the current and voltage are in$-$phase. a$.$ what is the frequency of the ac source? b$.$ what is the rms current when the switch is moved to position B$?$