# Question #b95b1

Oct 4, 2016

Let the resistance of the original coil of electromanet be $R \Omega$

For given V = 122V and I =12A

$R = \frac{V}{I} = \frac{122}{14}$

(a) Let ${r}_{1} \Omega$ be the resistance to be connected in series to limit the current to the rated value of 12A.

So $\frac{122}{R + {r}_{1}} = 12$

$\implies {r}_{1} = \frac{122}{12} - R = \frac{122}{12} - \frac{122}{14} = \frac{122 \times 2}{12 \times 14}$

$= 1.45 \Omega$

(b) Let ${r}_{2} \Omega$ be the resistance to be connected in series to limit the current to the of 9A.

So $\frac{122}{R + {r}_{2}} = 9$

$\implies {r}_{2} = \frac{122}{9} - R = \frac{122}{9} - \frac{122}{14} = \frac{122 \times 5}{9 \times 14}$

$= 4.84 \Omega$