I just spent two lectures in different subjects listening to the same lecture, an interesting lecture by a really nice professor. One was 1.5 hours long for a climate change class and the other was 3 hours long for an Energy systems class and the basis for both lectures was the same - nuclear energy. He used the same presentation, but it was interesting to see how he modified his speed and delivery and the points he focussed on both times depending on the class.
The best part was he gives out suckers to everyone at the end of the class to illustrate the power of nuclear energy, and I got one for both lectures.