A device X converts ac input into a unidirectional, pulsating and intermittent output. The device X is a
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → Half Wave Rectifier
A diode conducts only when it is forward biased. In a half-wave rectifier a single diode conducts during one half of each input cycle and blocks the other half. The output is:
\( \text{unidirectional}: \text{the current always flows in one direction} \)
\( \text{pulsating}: \text{its value rises and falls within each half cycle} \)
\( \text{intermittent}: \text{it is zero for every alternate half cycle} \)
Why the other options are incorrect
Option (1) Battery Eliminator — Incorrect. A battery eliminator converts ac mains into a steady dc supply using a rectifier, a filter and usually a regulator; its output is not intermittent.
Option (2) Full Wave Rectifier — Incorrect. A full-wave rectifier gives pulsating output in both half cycles, with no gaps, so it is not intermittent.
Option (4) Alternator — Incorrect. An alternator is an ac generator; it converts mechanical energy into ac, not ac into unidirectional output.
NCERT (2026-27):
Application of Junction Diode as a Rectifier – “… If an alternating voltage is applied across a diode in series with a load, a pulsating voltage will appear across the load only during the half cycles of the ac input during which the diode is forward biased. Such rectifier circuit, as shown in Fig. 14.18, is called a half-wave rectifier. … Therefore, in the positive half-cycle of ac there is a current through the load resistor \( R_L \) and we get an output voltage, as shown in Fig. 14.18(b), whereas there is no current in the negative half-cycle. … Thus, the output voltage, though still varying, is restricted to only one direction and is said to be rectified.”
