Trains can be electrified either with DC voltage or with AC voltage. Various networks across various countries uses various standards.
My question is however for trams, which are basically a lighter version of a train who is able to criculate on streets. (I am fully aware some networks are in between trams and trains). All of them seems to be electrified with low-voltage DC, with the exeption of T4 in Paris and the T11-express in Paris which are more like a light-metro than a tram.
Why are trams never electrified with AC ?