Consider the following statements about a half-wave rectifier:
(A) The output is obtained only for half of the input ac wave.
(B) The reverse breakdown voltage of the diode should be higher than the peak ac voltage at the secondary of the transformer.
(C) The output voltage is in one direction, but it keeps varying.
(D) In the negative half-cycle, a large reverse current flows through the load \(R_L\).
Which of the above statements are incorrect?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (D) only
A diode conducts only when it is forward biased. So in a half-wave rectifier the load gets current in one half-cycle and almost none in the other.
(A) The output is obtained only for half of the input ac wave. — Correct statement. The diode conducts only in the half-cycles in which it is forward biased. That is why the circuit is called a half-wave rectifier.
(B) The reverse breakdown voltage of the diode should be higher than the peak ac voltage at the secondary of the transformer. — Correct statement. In the negative half-cycle the full peak voltage acts across the diode in reverse. A higher breakdown voltage keeps the diode safe.
(C) The output voltage is in one direction, but it keeps varying. — Correct statement. The output comes as separate pulses. They are all in one direction, but the value is not steady.
(D) In the negative half-cycle, a large reverse current flows through the load \(R_L\). — Incorrect statement. In this half-cycle the diode is reverse biased. Its reverse saturation current is so small that it is taken as zero, so no current flows through the load.
NCERT (2026-27):
Application of Junction Diode as a Rectifier – “… Since the rectified output of this circuit is only for half of the input ac wave it is called as half-wave rectifier.”
Application of Junction Diode as a Rectifier – “… (The reverse breakdown voltage of the diode must be sufficiently higher than the peak ac voltage at the secondary of the transformer to protect the diode from reverse breakdown.)”
Application of Junction Diode as a Rectifier – “… Thus, the output voltage, though still varying, is restricted to only one direction and is said to be rectified. …”
Application of Junction Diode as a Rectifier – “Therefore, in the positive half-cycle of ac there is a current through the load resistor RL … whereas there is no current in the negative half-cycle. …”