The process of converting alternating current into direct current is known as
A. modulation
B. amplification
C. detection
D. rectification

Hint: The alternating current has two directions: positive and negative. In order to convert alternating current into direct current, we need a device which can strip off one of the positive or negative parts of the alternating signal and we obtain a signal which flows in only one direction making direct current.

Complete answer:
The simplest device which is used to convert alternating current into direct current is known as rectifier.
The basic working principle of a rectifier is to block the flow of current which is in the negative direction but will allow the current in positive direction to pass through it. This property allows the rectifier to convert an AC signal into DC signal since the rectifier removes the negative part of the signal with only the positive part as the output.
The image shows a bridge rectifier which performs full wave rectification. As we can see, the input signal has voltage in both positive and negative direction but the output signal has only positive values of voltage. This means that the rectifier has prevented the flow in negative or opposite direction by turning negative voltages into positive voltages.


Hence, the correct answer is option D since a rectifier produces rectification.

Note:
1. The modulation is a technique in which a type of wave is superimposed on another type of wave mostly for communication purposes. It can be performed in three ways which are amplitude modulation, frequency modulation and phase modulation.
2. Amplification means that we are increasing the amplitude of an input signal. The devices which can perform amplification include transistor amplifier and operational amplifier.