| Statement I: An electric motor will have maximum efficiency when back emf becomes equal to half of applied emf. |
| Statement II: Efficiency of electric motor depends only on magnitude of back emf. |
A) Statement I is true; Statement B is true; Statement B is not a correct explanation for Statement I,
B) Statement I is true; Statement II is false.
C) Statement I is false; Statement II is true.
D) Statement I is true; Statement II is true; Statements is the correct explanation for Statement I.
Correct Answer: B
Solution :
Since, the efficiency of an electric motor is given by \[\eta \frac{\text{output power}}{\text{input power}}\] From the above-relation, it is quite clear that maximum output power corresponds maximum efficiency of motor. Now, output power is given by \[=ei=\frac{e(E-e)}{R}\] To obtain maximum output power differentiating Eq. (i) with respect to e which will be equal to zero. So, \[\frac{d}{de}\left[ \frac{e(E-e)}{R} \right]=0\Rightarrow e=\frac{E}{2}\] Thus, when back emf becomes equal to half of the applied emf, the efficiency of motor will be maximum.
You need to login to perform this action.
You will be redirected in
3 sec
