Introduction:
A rectifier is an electrical device that converts alternating current (AC) to direct current (DC). There are two main types of rectifiers: half-wave rectifier and full-wave rectifier. The difference between these two rectifiers lies in their ability to convert AC voltage to DC voltage. The equivalent DC output voltage of a full-wave rectifier is double that of a half-wave rectifier.

Half-Wave Rectifier:
A half-wave rectifier is a simple rectifier circuit that uses a diode to convert AC voltage to DC voltage. It allows only one half of the AC waveform to pass through, while blocking the other half. As a result, the output waveform is a pulsating DC voltage with only positive half-cycles.

Full-Wave Rectifier:
A full-wave rectifier is a more efficient rectifier circuit that uses two diodes and a center-tapped transformer. It allows both halves of the AC waveform to pass through, converting them into positive half-cycles. This results in a smoother output waveform compared to a half-wave rectifier.

Explanation:
The equivalent DC output voltage of a rectifier is a measure of the average value of the rectified waveform. In the case of a half-wave rectifier, the output waveform is a series of positive half-cycles. The average value of this waveform is half of the peak value of the positive half-cycle.

On the other hand, a full-wave rectifier produces a waveform with positive half-cycles on both sides of the x-axis. This means that the average value of the rectified waveform is equal to the peak value of the positive half-cycle.

Since the peak value of the positive half-cycle in a full-wave rectifier is twice that of a half-wave rectifier, the average value (equivalent DC output voltage) of the full-wave rectifier is also twice that of a half-wave rectifier.

Therefore, the correct answer is option 'D' - double. The equivalent DC output voltage of a full-wave rectifier is double the equivalent DC output voltage of a half-wave rectifier.