Voltage source in AC

Hi.
i'm studing an inductor to analyze inductance and resistence od the model.
I use electrical circuit and i work with AC frequency of about 20kHz and i have some questions:

1)Vsrc in voltage source is a rms value(effective value)?
2)Why i have to add a resistence in series with my circuit to work? So if i use only voltage source and External IvsU the program doesn't work. It works only if i add a resistence after the external IvsU (serie).

Thanks
Nicola