A Cambridge Municipal Judge is introducing offenders tot he finer points of Polka. Judge John Mark Nicholson sentenced a 19-year-old Derwent man to listen to four hours of recordings by Frankie “the Polka King” Yankovic. The man’s crime? Cruising through Cambridge last month with his car windows rolled down and the stereo cranked up. Alan “AJ” Law was cited for disorderly conduct. When he appeared before Judge Nicholson he was given a choice: pay or polka. Law opted for the music, avoiding a one-hundred-dollar fine. Law served his sentence yesterday, sitting in a police interview room from nine AM to one PM.