PhysicsCBSE Class 12 · Board exam 2024, set 55/1/1 · 4 marks · Case-based

CBSE Class 12 Physics 2024: question 30

Set in the CBSE Class 12 board exam of 2024, paper 55/1/1, section D, question 30, for 4 marks. Try it first; the hints and our step-by-step solution are below.

Q30 · 4 marks · Case-basedCompetency-basedSemiconductor Electronics: Materials, Devices and Simple Circuits

Junction Diode as a Rectifier :
The process of conversion of an ac voltage into a dc voltage is called rectification and the device which performs this conversion is called a rectifier. The characteristics of a p-n junction diode reveal that when a p-n junction diode is forward biased, it offers a low resistance and when it is reverse biased, it offers a high resistance. Hence, a p-n junction diode conducts only when it is forward biased. This property of a p-n junction diode makes it suitable for its use as a rectifier.
Thus, when an ac voltage is applied across a p-n junction, it conducts only during those alternate half cycles for which it is forward biased. A rectifier which rectifies only half cycle of an ac voltage is called a half-wave rectifier and one that rectifies both the half cycles is known as a full-wave rectifier.

(i)
The root mean square value of an alternating voltage applied to a full-wave rectifier is $\frac{V _{0}}{2}$ . Then the root mean square value of the rectified output voltage is :
1. (A) $\frac{V _{0}}{2}$
2. (B) $\frac{V _{0}^{2}}{2}$
3. (C) $\frac{2 V _{0}}{2}$
4. (D) $\frac{V _{0}}{2 2}$
1 mark
(ii)
In a full-wave rectifier, the current in each of the diodes flows for :
1. (A)Complete cycle of the input signal
2. (B)Half cycle of the input signal
3. (C)Less than half cycle of the input signal
4. (D)Only for the positive half cycle of the input signal
1 mark
(iii)
In a full-wave rectifier :
1. (A)Both diodes are forward biased at the same time.
2. (B)Both diodes are reverse biased at the same time.
3. (C)One is forward biased and the other is reverse biased at the same time.
4. (D)Both are forward biased in the first half of the cycle and reverse biased in the second half of the cycle.
1 mark
(iv)(a)
An alternating voltage of frequency of 50 Hz is applied to a half-wave rectifier. Then the ripple frequency of the output will be :
1. (A)100 Hz
2. (B)50 Hz
3. (C)25 Hz
4. (D)150 Hz
1 mark
OR
(iv)(b)
A signal, as shown in the figure, is applied to a p-n junction diode. Identify the output across resistance $R_{L}$ :
1. (A)Pulse going up to 10 V
2. (B)Pulse going down to $- 10$ V
3. (C)Pulse going down to $- 5$ V
4. (D)Pulse going up to $+ 5$ V
1 mark

Figure in the paper: Figure for (iv)(b): input is a rectangular pulse between $- 5$ V and $+ 5$ V (dashed line at 0 V) applied to a series diode followed by load resistance $R_{L}$ across the output terminals. Options are output waveforms: (A) pulse to 10 V, (B) inverted pulse to $- 10$ V, (C) inverted pulse to $- 5$ V, (D) pulse to $+ 5$ V. See it in the official paper.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 55/1/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

Does flipping the sign of half the waveform change its mean square value?

Hint 2

In a full-wave rectifier the two diodes take turns to conduct.

Hint 3

A half-wave rectifier passes one half of each input cycle; a diode passes only the polarity that forward-biases it.

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

(i) Full-wave rectification only flips the negative half cycles to positive. The square of the voltage, and hence the rms value, is unchanged: $V_{r m s} = \frac{V _{0}}{2}$ . Option (A).
1 mark
(ii) Each diode conducts only in the half cycle in which it is forward biased. Option (B).
1 mark
(iii) In each half cycle one diode is forward biased while the other is reverse biased. Option (C).
1 mark
(iv)(a) A half-wave rectifier gives one output pulse per input cycle, so the ripple frequency is 50 Hz. Option (B).
1 mark
(iv)(b) The diode conducts only for the +5 V part of the input and blocks the −5 V part. The output across $R_{L}$ is a set of pulses rising to +5 V, and zero otherwise. Option (D).

Answer: (i) A; (ii) B; (iii) C; (iv)(a) B; (iv)(b) D

Where the marks are

(i) $V_{0} / 2$ – option A (1 mark)
(ii) half cycle – option B (1 mark)
(iii) one forward, one reverse biased – option C (1 mark)
(iv)(a) 50 Hz – option B, or (iv)(b) pulse up to +5 V – option D (1 mark)

Revise the chapter

Chapter: Semiconductor Electronics: Materials, Devices and Simple Circuits (notes, formulas, where marks are lost and every past question)
Topic: Diode as a Rectifier

Practise this chapterBoard-style questions from Semiconductor Electronics: Materials, Devices and Simple Circuits, one at a time, marked against the answer key and marking points.Back to the full paper2024 board paper, set 55/1/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.

CBSE Class 12 Physics 2024: question 30

Hints

Step-by-step solution

Revise the chapter

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