Explanation:
When a capacitor is connected across the output terminals of a half or full-wave rectifier, the output voltage essentially becomes a DC voltage.

Rectification:
Rectification is the process of converting an alternating current (AC) into a direct current (DC). A rectifier is used to perform this conversion. Half-wave and full-wave rectifiers are commonly used rectification circuits.

Half-wave rectifier:
In a half-wave rectifier, only one half of the input AC waveform is utilized. The diode in the circuit allows the positive half of the input AC waveform to pass through, while blocking the negative half. As a result, the output waveform consists of only the positive half of the input waveform.

Full-wave rectifier:
In a full-wave rectifier, both halves of the input AC waveform are utilized. The circuit uses a combination of diodes to allow both the positive and negative halves of the input waveform to pass through. This results in a full-wave rectified output waveform.

Output voltage:
The output voltage of a rectifier without a capacitor connected across the output terminals is a pulsating DC voltage. This voltage varies in amplitude but does not have a constant value. It consists of a series of positive pulses for a half-wave rectifier and a series of positive and negative pulses for a full-wave rectifier.

Effect of capacitor:
When a capacitor is connected across the output terminals of a rectifier, it acts as a filter. It smoothens the pulsating DC voltage and converts it into a more stable DC voltage.

Charging and discharging of capacitor:
During the positive half-cycle of the rectified waveform, the capacitor charges up to the peak voltage of the rectified waveform. During the negative half-cycle, the capacitor discharges through the load. This charging and discharging process results in a more continuous and stable DC voltage across the load.

Effect of capacitor on output voltage:
The presence of the capacitor across the output terminals of the rectifier eliminates the pulsations and fluctuations in the output voltage. The capacitor holds a charge during the charging phase and discharges slowly during the discharging phase, maintaining a relatively constant voltage across the load.

DC voltage:
As a result, the output voltage essentially becomes a DC voltage. Although there may be some ripple voltage (small AC component) remaining due to the capacitor's charging and discharging cycle, it is significantly reduced compared to the rectified voltage without the capacitor. The remaining ripple can be further minimized by increasing the capacitance value of the capacitor.

Therefore, the correct answer is option 'A': The output voltage essentially becomes a DC voltage.