In a hydroelectric dam, what is the sequence of energy transformations as water drives the turbine and generator?

• A. Electrical → light → mechanical
• B. Chemical → mechanical → electrical
• C. Mechanical → chemical → light
• D. Mechanical → electrical → light

Answer: (D)

In a hydroelectric dam, energy changes form in stages. The moving water imparts mechanical energy to the turbine as it drives it to rotate. That rotational, mechanical energy is then converted into electrical energy by the generator. The electricity can be used to power loads like lights, so electrical energy is transformed into light energy. So the sequence is mechanical → electrical → light. Chemical changes don’t occur in this energy flow, and the light step is the end-use of the electricity produced.