What device is responsible for changing AC to DC?

The device that is responsible for changing alternating current (AC) to direct current (DC) is a rectifier. A rectifier works by allowing current to flow in one direction while blocking it in the opposite direction. This is typically achieved using semiconductor materials like diodes, which can conduct current when forward-biased but block it when reverse-biased. Rectifiers are crucial in power supply applications where DC is required, such as in battery charging or in powering electronic devices.

In contrast, a transformer is used to change the voltage level of AC but does not convert AC to DC; it works based on electromagnetic induction. A generator converts mechanical energy into electrical energy, producing AC or, in some cases, DC depending on its design. A commutator is a device used in conjunction with generators and motors to convert generated AC into DC but is not in itself responsible for the conversion. Therefore, a rectifier is the correct answer as it directly refers to the process of converting AC electricity to DC.