Answer to Question #259377 in Electricity and Magnetism for yuu

Question

 It is desired to have a current of 20 A in a 5- resistor when it is connected to an 80-V battery. Is there any way in which an auxiliary resistor can be connected in the circuit to increase the current in the 5- resistor to this valur? If so, what should ist resistance be?

Answer 1

Assume x ohm resistor connected in parallel combination

$\frac{1}{R_{eq}}=\frac{1}{R_1}+\frac{1}{R_2}$

$R_{eq}=\frac{R_1R_2}{R_1+R_2}$

$R_{eq}=\frac{5X}{5+X}$

$V=IR_{eq}$

Put value

$80=20\times\frac{5X}{5+X}$

$20+4X=5X$

$X=20\Omega$

X=20 $\Omega$ connected in parallel combination of 5$\Omega$