Final answer:
In a coal-fired power plant, the turbine turning the generator converts mechanical energy into electrical energy.
Step-by-step explanation:
In a conventional coal-fired electrical power plant, the process that takes place involves multiple steps of energy conversion. Initially, the chemical energy contained in coal is converted into thermal energy as it burns. This thermal energy is used to turn water into steam in a boiler. Subsequently, the steam's thermal energy is converted into mechanical energy as it spins a turbine. Finally, this mechanical energy is converted into electrical energy by the generator. Therefore, when referring to the turbine turning the generator, the form of energy conversion is mechanical to electrical.