Watch the scene again. He does that little glowy thing in his hand for awhile where Dooku's blast hits his hand and does nothing. Then he pushes his hand forward and throws lightning in Dooku's face. Dooku BLOCKS it with his hand and sends it into the ceiling where it explodes in flames.
That's the only time in any of the movies where we see anything like it. It isn't even the same as the scene where in that stalemate with Palpatine in Episode III.
Somebody once suggested that here Yoda isn't using the same hand gesture as Dooku, so he must not "really" be throwing it, but if you watch Episode III and ROTJ you see that there is no single universal hand gesture for "lightning" (just like there isn't one for any other Force ability used in more than one movie, and sometimes they use the force without any gestures, though lightning always appears to come forth from a hand somehow).