Help with science article

Hi,
Im writting a science journal article on cooling. I was wondering whether someone could help explain to me exactly why a cpu gives off heat. please make it a nice n easy explainanation because the audience of the science journal arne't all that interested in IT.

heat

Electricity coursing thru circuits... there's some resistence in all conductive materials. Resistence converts some of the electricity into thermal energy. Look up the equations. CPU's have silicon and copper innerds.