358414
Statement A : The back emf in a dc motor is maximum when the motor has just been switched on. Statement B : When motor is switched on, it has maximum speed.
1 Statement A is correct but Statement B is incorrect.
2 Statement A is incorrect but Statement B is correct.
3 Both statements are correct.
4 Both Statements are incorrect.
Explanation:
Back emf is actually the induced emf produced in motor. When motor is just switched on, the magnitude of back emf is quite small due to the low speed of the motor.
PHXII06:ELECTROMAGNETIC INDUCTION
358415
Assertion : An electric motor will have maximum efficiency when back emf becomes equal to half of applied \(emf\). Reason : Efficiency of electric motor depends only on magnitude of back \(emf\).
1 Both Assertion and Reason are correct and Reason is the correct explanation of the Assertion.
2 Both Assertion and Reason are correct but Reason is not the correct explanation of the Assertion.
3 Assertion is correct but Reason is incorrect.
4 Both Assertion and Reason are incorrect.
Explanation:
An electric motor will have maximum efficiency when the back electromotive force (emf) becomes equal to half of the applied emf. This is because at this point, the motor is operating at an optimal balance between back emf and applied emf, maximizing the efficiency of the motor. The efficiency of an electric motor depends on several factors, not just the magnitude of back emf. It also depends on factors such as the resistance in the motor windings and the mechanical load on the motor. The relationship between back emf and applied emf is just one aspect of motor efficiency, but it does not solely determine motor efficiency. Therefore, while the assertion is correct, the reason is not the correct explanation for the assertion.
AIIMS - 2008
PHXII06:ELECTROMAGNETIC INDUCTION
358416
Assertion : An electric motor will have maximum efficiency when back emf becomes equal to half of applied \(emf.\) Reason : Efficiency of electric motor does not depend on magnitude of back \(emf.\)
1 Both Assertion and Reason are correct and Reason is the correct explanation of the Assertion.
2 Both Assertion and Reason are correct but Reason is not the correct explanation of the Assertion.
3 Assertion is correct but Reason is incorrect.
4 Assertion is incorrect but reason is correct.
Explanation:
Maximum efficiency in an electric motor is achieved when the back electromotive force (back emf) approaches the applied electromotive force (applied emf). Specifying an exact ratio of "half" is an approximation and might not hold true for all motor designs and applications. The reason is inaccurate in stating that motor efficiency depends solely on the magnitude of back emf. In reality, motor efficiency is influenced by various other factors, such as resistive losses, mechanical friction losses. Assertion is true but reason is false. So, correct option is (3).
358414
Statement A : The back emf in a dc motor is maximum when the motor has just been switched on. Statement B : When motor is switched on, it has maximum speed.
1 Statement A is correct but Statement B is incorrect.
2 Statement A is incorrect but Statement B is correct.
3 Both statements are correct.
4 Both Statements are incorrect.
Explanation:
Back emf is actually the induced emf produced in motor. When motor is just switched on, the magnitude of back emf is quite small due to the low speed of the motor.
PHXII06:ELECTROMAGNETIC INDUCTION
358415
Assertion : An electric motor will have maximum efficiency when back emf becomes equal to half of applied \(emf\). Reason : Efficiency of electric motor depends only on magnitude of back \(emf\).
1 Both Assertion and Reason are correct and Reason is the correct explanation of the Assertion.
2 Both Assertion and Reason are correct but Reason is not the correct explanation of the Assertion.
3 Assertion is correct but Reason is incorrect.
4 Both Assertion and Reason are incorrect.
Explanation:
An electric motor will have maximum efficiency when the back electromotive force (emf) becomes equal to half of the applied emf. This is because at this point, the motor is operating at an optimal balance between back emf and applied emf, maximizing the efficiency of the motor. The efficiency of an electric motor depends on several factors, not just the magnitude of back emf. It also depends on factors such as the resistance in the motor windings and the mechanical load on the motor. The relationship between back emf and applied emf is just one aspect of motor efficiency, but it does not solely determine motor efficiency. Therefore, while the assertion is correct, the reason is not the correct explanation for the assertion.
AIIMS - 2008
PHXII06:ELECTROMAGNETIC INDUCTION
358416
Assertion : An electric motor will have maximum efficiency when back emf becomes equal to half of applied \(emf.\) Reason : Efficiency of electric motor does not depend on magnitude of back \(emf.\)
1 Both Assertion and Reason are correct and Reason is the correct explanation of the Assertion.
2 Both Assertion and Reason are correct but Reason is not the correct explanation of the Assertion.
3 Assertion is correct but Reason is incorrect.
4 Assertion is incorrect but reason is correct.
Explanation:
Maximum efficiency in an electric motor is achieved when the back electromotive force (back emf) approaches the applied electromotive force (applied emf). Specifying an exact ratio of "half" is an approximation and might not hold true for all motor designs and applications. The reason is inaccurate in stating that motor efficiency depends solely on the magnitude of back emf. In reality, motor efficiency is influenced by various other factors, such as resistive losses, mechanical friction losses. Assertion is true but reason is false. So, correct option is (3).
358414
Statement A : The back emf in a dc motor is maximum when the motor has just been switched on. Statement B : When motor is switched on, it has maximum speed.
1 Statement A is correct but Statement B is incorrect.
2 Statement A is incorrect but Statement B is correct.
3 Both statements are correct.
4 Both Statements are incorrect.
Explanation:
Back emf is actually the induced emf produced in motor. When motor is just switched on, the magnitude of back emf is quite small due to the low speed of the motor.
PHXII06:ELECTROMAGNETIC INDUCTION
358415
Assertion : An electric motor will have maximum efficiency when back emf becomes equal to half of applied \(emf\). Reason : Efficiency of electric motor depends only on magnitude of back \(emf\).
1 Both Assertion and Reason are correct and Reason is the correct explanation of the Assertion.
2 Both Assertion and Reason are correct but Reason is not the correct explanation of the Assertion.
3 Assertion is correct but Reason is incorrect.
4 Both Assertion and Reason are incorrect.
Explanation:
An electric motor will have maximum efficiency when the back electromotive force (emf) becomes equal to half of the applied emf. This is because at this point, the motor is operating at an optimal balance between back emf and applied emf, maximizing the efficiency of the motor. The efficiency of an electric motor depends on several factors, not just the magnitude of back emf. It also depends on factors such as the resistance in the motor windings and the mechanical load on the motor. The relationship between back emf and applied emf is just one aspect of motor efficiency, but it does not solely determine motor efficiency. Therefore, while the assertion is correct, the reason is not the correct explanation for the assertion.
AIIMS - 2008
PHXII06:ELECTROMAGNETIC INDUCTION
358416
Assertion : An electric motor will have maximum efficiency when back emf becomes equal to half of applied \(emf.\) Reason : Efficiency of electric motor does not depend on magnitude of back \(emf.\)
1 Both Assertion and Reason are correct and Reason is the correct explanation of the Assertion.
2 Both Assertion and Reason are correct but Reason is not the correct explanation of the Assertion.
3 Assertion is correct but Reason is incorrect.
4 Assertion is incorrect but reason is correct.
Explanation:
Maximum efficiency in an electric motor is achieved when the back electromotive force (back emf) approaches the applied electromotive force (applied emf). Specifying an exact ratio of "half" is an approximation and might not hold true for all motor designs and applications. The reason is inaccurate in stating that motor efficiency depends solely on the magnitude of back emf. In reality, motor efficiency is influenced by various other factors, such as resistive losses, mechanical friction losses. Assertion is true but reason is false. So, correct option is (3).
