In a geothermal power plant, what turns the turbine that generates electricity?

• A. Water
• B. Hot air
• C. Steam
• D. Lava

Answer: (C)

Steam is the working fluid that turns the turbine in a geothermal power plant. The underground heat heats water to produce steam, and the high-pressure steam expands and flows through the turbine blades, transferring its energy as rotational motion. This rotation drives the generator to produce electricity. Liquid water doesn’t provide the same expansion energy to spin the turbine, hot air isn’t part of the geothermal process, and lava isn’t involved in generating power. (Some designs use a secondary fluid heated by geothermal heat, but the turbine is still powered by vapor, i.e., steam-like working fluid.)