This entirely depends on what motor that sits inside the oven and how it was designed. I wouldn't assume that every microwave that has ever been made is using the same kind of motor. You'll have to come up with some manner of partnumber or preferably a datasheet of the motor, or I don't think this question can be answered.

Be careful, my dude. People don't take questions about microwaves too well here.

As for the question "what is AC frequency", that's a valid question. Alternating currents means you have several phases (simply put: several signals/wires) between which the current alternates. The current in each phase comes as a sine wave and the "AC frequency" is simply the (2*PI) period of the sine wave. So at 50Hz one phase will have 1/50=20ms between sine wave peaks. And this frequency, as well as the AC voltage, are poorly specified around the world. The most common is 230VAC/50Hz.

@Kranulis - now that you mention it... girlfriend's fine brand microwave just made a viciously loud "snap" noise over the weekend, which I figure is the magnetron. wanted to do a dissection for the turntable // UPDATE - supposedly working again. oh well

Your only real remedy is to test or research your next microwave purchase. They have various rotation speeds depending on the gear ratio chosen for the synchronous motor. It can vary quite a bit so you may find a suitable speed for your local line frequency when you replace or swap the unit one day.