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Assertion (A) : It is necessary to keep the thyristor reverse biased for a finite period before a forward anode voltage can be reapplied.
Reason (R) : Once the SCR starts conducting an appreciable forward current, the gate has no control on it and the device can be brought back to the blocking state only by reducing the forward current level below that of the holding current.
Reason (R) : Once the SCR starts conducting an appreciable forward current, the gate has no control on it and the device can be brought back to the blocking state only by reducing the forward current level below that of the holding current.
- a)Both A and R are true and R is the correct explanation of A.
- b)Both A and R are true but R is not the correct explanation of A
- c)A is true but R is false.
- d)A is false but R is true.
Correct answer is option 'B'. Can you explain this answer?
Verified Answer
Assertion (A) : It is necessary to keep the thyristor reverse biased f...
It is necessary to keep the thyristor reverse biased for a finite period before a forward anode voltage can be reapplied because if a forward voltage is applied immediately after reducing the anode current to zero, it will not block the forward voltage and will start conducting again, although it is not triggered by a gate pulse. Reason is also a true statement but not the correct explanation of assertion.
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Assertion (A) : It is necessary to keep the thyristor reverse biased f...
Assertion (A): It is necessary to keep the thyristor reverse biased for a finite period before a forward anode voltage can be reapplied.
Reason (R): Once the SCR starts conducting an appreciable forward current, the gate has no control on it and the device can be brought back to the blocking state only by reducing the forward current level below that of the holding current.
Explanation:
To understand the assertion and reason given in the question, let's first understand the working principle of a thyristor or silicon-controlled rectifier (SCR).
A thyristor is a four-layer, three-junction semiconductor device that can control the flow of current. It has three terminals - anode, cathode, and gate. The thyristor can be turned on or triggered into conduction by applying a positive pulse at the gate terminal. Once it is turned on, it remains conducting even if the gate pulse is removed until the anode current drops below a certain level known as the holding current.
Now let's analyze the given assertion and reason:
Assertion (A): It is necessary to keep the thyristor reverse biased for a finite period before a forward anode voltage can be reapplied.
When a thyristor is conducting a forward current and we want to turn it off, we need to make it reverse biased. This is because the thyristor can only be turned off when it is in the reverse blocking mode. By applying a reverse voltage, we reduce the anode current below the holding current level, and the thyristor turns off.
Therefore, assertion (A) is true.
Reason (R): Once the SCR starts conducting an appreciable forward current, the gate has no control on it and the device can be brought back to the blocking state only by reducing the forward current level below that of the holding current.
The reason given states that once the thyristor starts conducting a forward current, the gate loses control over it, and the only way to bring it back to the blocking state is by reducing the forward current below the holding current level.
This reason is also correct because once the thyristor is triggered into conduction, it becomes a self-sustaining device and can maintain conduction without any external control. The gate pulse is required only to trigger the thyristor initially, and it does not have control over the thyristor's conduction once it is turned on. To turn off the thyristor, the forward current must be reduced below the holding current level.
Therefore, reason (R) is also true.
Explanation of Correct Answer:
Both the assertion and reason are true, and the reason correctly explains the assertion. When a thyristor is conducting a forward current, it can only be turned off by reducing the forward current below the holding current level. Before reapplying a forward anode voltage, it is necessary to keep the thyristor reverse biased for a finite period to ensure that the forward current is reduced below the holding current level.
Hence, the correct answer is option 'B' - Both A and R are true, but R is not the correct explanation of A.
Reason (R): Once the SCR starts conducting an appreciable forward current, the gate has no control on it and the device can be brought back to the blocking state only by reducing the forward current level below that of the holding current.
Explanation:
To understand the assertion and reason given in the question, let's first understand the working principle of a thyristor or silicon-controlled rectifier (SCR).
A thyristor is a four-layer, three-junction semiconductor device that can control the flow of current. It has three terminals - anode, cathode, and gate. The thyristor can be turned on or triggered into conduction by applying a positive pulse at the gate terminal. Once it is turned on, it remains conducting even if the gate pulse is removed until the anode current drops below a certain level known as the holding current.
Now let's analyze the given assertion and reason:
Assertion (A): It is necessary to keep the thyristor reverse biased for a finite period before a forward anode voltage can be reapplied.
When a thyristor is conducting a forward current and we want to turn it off, we need to make it reverse biased. This is because the thyristor can only be turned off when it is in the reverse blocking mode. By applying a reverse voltage, we reduce the anode current below the holding current level, and the thyristor turns off.
Therefore, assertion (A) is true.
Reason (R): Once the SCR starts conducting an appreciable forward current, the gate has no control on it and the device can be brought back to the blocking state only by reducing the forward current level below that of the holding current.
The reason given states that once the thyristor starts conducting a forward current, the gate loses control over it, and the only way to bring it back to the blocking state is by reducing the forward current below the holding current level.
This reason is also correct because once the thyristor is triggered into conduction, it becomes a self-sustaining device and can maintain conduction without any external control. The gate pulse is required only to trigger the thyristor initially, and it does not have control over the thyristor's conduction once it is turned on. To turn off the thyristor, the forward current must be reduced below the holding current level.
Therefore, reason (R) is also true.
Explanation of Correct Answer:
Both the assertion and reason are true, and the reason correctly explains the assertion. When a thyristor is conducting a forward current, it can only be turned off by reducing the forward current below the holding current level. Before reapplying a forward anode voltage, it is necessary to keep the thyristor reverse biased for a finite period to ensure that the forward current is reduced below the holding current level.
Hence, the correct answer is option 'B' - Both A and R are true, but R is not the correct explanation of A.
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Assertion (A) : It is necessary to keep the thyristor reverse biased for a finite period before a forward anode voltage can be reapplied.Reason (R) : Once the SCR starts conducting an appreciable forward current, the gate has no control on it and the device can be brought back to the blocking state only by reducing the forward current level below that of the holding current.a)Both A and R are true and R is the correct explanation of A.b)Both A and R are true but R is not the correct explanation of Ac)A is true but R is false.d)A is false but R is true.Correct answer is option 'B'. Can you explain this answer? for Electrical Engineering (EE) 2026 is part of Electrical Engineering (EE) preparation. The Question and answers have been prepared according to the Electrical Engineering (EE) exam syllabus. Information about Assertion (A) : It is necessary to keep the thyristor reverse biased for a finite period before a forward anode voltage can be reapplied.Reason (R) : Once the SCR starts conducting an appreciable forward current, the gate has no control on it and the device can be brought back to the blocking state only by reducing the forward current level below that of the holding current.a)Both A and R are true and R is the correct explanation of A.b)Both A and R are true but R is not the correct explanation of Ac)A is true but R is false.d)A is false but R is true.Correct answer is option 'B'. Can you explain this answer? covers all topics & solutions for Electrical Engineering (EE) 2026 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for Assertion (A) : It is necessary to keep the thyristor reverse biased for a finite period before a forward anode voltage can be reapplied.Reason (R) : Once the SCR starts conducting an appreciable forward current, the gate has no control on it and the device can be brought back to the blocking state only by reducing the forward current level below that of the holding current.a)Both A and R are true and R is the correct explanation of A.b)Both A and R are true but R is not the correct explanation of Ac)A is true but R is false.d)A is false but R is true.Correct answer is option 'B'. Can you explain this answer?.
Assertion (A) : It is necessary to keep the thyristor reverse biased for a finite period before a forward anode voltage can be reapplied.Reason (R) : Once the SCR starts conducting an appreciable forward current, the gate has no control on it and the device can be brought back to the blocking state only by reducing the forward current level below that of the holding current.a)Both A and R are true and R is the correct explanation of A.b)Both A and R are true but R is not the correct explanation of Ac)A is true but R is false.d)A is false but R is true.Correct answer is option 'B'. Can you explain this answer? for Electrical Engineering (EE) 2026 is part of Electrical Engineering (EE) preparation. The Question and answers have been prepared according to the Electrical Engineering (EE) exam syllabus. Information about Assertion (A) : It is necessary to keep the thyristor reverse biased for a finite period before a forward anode voltage can be reapplied.Reason (R) : Once the SCR starts conducting an appreciable forward current, the gate has no control on it and the device can be brought back to the blocking state only by reducing the forward current level below that of the holding current.a)Both A and R are true and R is the correct explanation of A.b)Both A and R are true but R is not the correct explanation of Ac)A is true but R is false.d)A is false but R is true.Correct answer is option 'B'. Can you explain this answer? covers all topics & solutions for Electrical Engineering (EE) 2026 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for Assertion (A) : It is necessary to keep the thyristor reverse biased for a finite period before a forward anode voltage can be reapplied.Reason (R) : Once the SCR starts conducting an appreciable forward current, the gate has no control on it and the device can be brought back to the blocking state only by reducing the forward current level below that of the holding current.a)Both A and R are true and R is the correct explanation of A.b)Both A and R are true but R is not the correct explanation of Ac)A is true but R is false.d)A is false but R is true.Correct answer is option 'B'. Can you explain this answer?.
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