Which device changes an alternating current into a varying direct current signal?

A rectifier is the device that changes alternating current (AC) into a varying direct current (DC) signal. The process involves using semiconductor components, such as diodes, which allow current to flow in one direction only.

In AC, the current alternates its direction and amplitude regularly, while in DC, the current flows in a single direction and typically has a constant voltage level. The rectifier accomplishes this by allowing only the positive (or negative) parts of the AC waveform to pass through, effectively “clipping” the negative cycle of the AC signal. When this is done, the output is a pulsed DC signal that can then be smoothed using filters to produce a more stable DC voltage.

This function is crucial in power supplies for electronic devices, where a stable DC output is needed to power components. Other options, such as a transformer, are used to change voltage levels in AC systems without converting the current type, while an amplifier increases the amplitude of signals but does not convert AC to DC. A reflector is unrelated to electrical signal conversion. Therefore, the rectifier's role is vital in the conversion process from AC to a usable form of DC.