Final answer:
The correct difference between energy transformations in power plants and dams is that dams directly use the kinetic energy of water to produce electricity, while traditional power plants use thermal energy from burning fuel or nuclear fission to generate steam that turns turbines.
Step-by-step explanation:
The primary difference between energy transformations in power plants and dams is in the initial energy source and the method of converting this energy into electricity. In the case of hydroelectric dams, potential energy stored in water at height is converted into kinetic energy as the water flows down. This kinetic energy then spins turbines, which in turn generate electricity through generators without releasing any by-products. Conversely, traditional power plants, that may use fossil fuels or nuclear fission, convert chemical or nuclear energy into thermal energy. The heat from burning fossil fuels or from a fission reaction boils water into steam, which then drives the turbines to produce electricity. It requires the consumption of a fuel source and may produce more by-products, including greenhouse gases in case of fossil fuels, and radioactive waste in case of nuclear fission.
Thus, the correct statement describing a difference between the two would be, 'Only dams use mechanical energy to produce electricity,' since they directly use the kinetic energy of flowing water for electricity generation without an intermediate thermal process. Power plants typically make use of thermal energy to create steam that turns turbines, except in the case of some renewable technologies like wind and solar power, which also use direct mechanical movement or light to generate electricity.