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A: When an electric motor is started, a ...

A: When an electric motor is started, a variable resistance (that decreases with time) is used in series. This resistance is known as motor slarter,
R: The back-emf in the beginning, when motor starts, is very small.

A

If both Assertion & Reason are true and the reason is the correct explanation of the assertion.

B

If both Assertion & Reason are true but the reason is not the correct explanation of the assertion.

C

If Assertion is true statement but Reason is false.

D

If both Assertion and Reason are false statements.

Text Solution

AI Generated Solution

The correct Answer is:
To solve the question, we need to analyze the two statements provided: the assertion (A) and the reason (R). ### Step-by-Step Solution: 1. **Understanding the Assertion (A)**: - The assertion states that when an electric motor is started, a variable resistance that decreases with time is used in series, known as a motor starter. - This is true because a motor starter is indeed used to limit the initial current flowing to the motor when it starts. The high initial current can damage the motor, so a variable resistance is employed to gradually increase the current as the motor speeds up. 2. **Understanding the Reason (R)**: - The reason states that the back-emf (electromotive force) at the beginning, when the motor starts, is very small. - This is also true. When the motor is at rest (not rotating), the back-emf is zero. As the motor starts to turn, the back-emf increases with speed. Therefore, at the very beginning, the back-emf is indeed very small. 3. **Relationship Between Assertion and Reason**: - The assertion explains the use of a motor starter, while the reason provides a justification for why the motor starter is necessary (due to the low back-emf at startup). - Since both statements are true and the reason correctly explains the assertion, we conclude that the assertion and reason are both valid. 4. **Conclusion**: - Both the assertion (A) and the reason (R) are true, and the reason is a correct explanation of the assertion. Therefore, the answer is that both statements are true and the reason is a correct explanation of the assertion. ### Final Answer: Both the assertion and the reason are true, and the reason is the correct explanation of the assertion. ---
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