Question #b95b1

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Answer 1 · 2016-10-04T12:25:57

Let the resistance of the original coil of electromanet be $ROmega$

For given V = 122V and I =12A

$R=V/I=122/14$

(a) Let $r_1 Omega$ be the resistance to be connected in series to limit the current to the rated value of 12A.

So $122/(R+r_1)=12$

$=>r_1=122/12-R=122/12-122/14=(122xx2)/(12xx14)$

$=1.45Omega$

(b) Let $r_2 Omega$ be the resistance to be connected in series to limit the current to the of 9A.

So $122/(R+r_2)=9$

$=>r_2=122/9-R=122/9-122/14=(122xx5)/(9xx14)$

$=4.84Omega$