Please help me setting the _alpha property on instance created with createEmptyMovieClip(). Following piece of code is not working the way I intended it to:

_root.createEmptyMovieClip("mc",2);
_root.mc.createTextField("t",10,250,200,200,50);
_root.mc._alpha=0;
_root.mc.t.text="Hello world";

Please tell me the way in which I can set the _alpha property of the instance created with createEmptyMovieClip() method.