As it is known to us, resistance of a circuit is inversely related to the current, we can write,
[tex] \frac{R_{1}}{R_{2}} =\frac{I_{2}}{I_{1}} [/tex]
Given, Rā= 5 ohms
Iā=12 A
Iā= 15 A
Substituting the values we get,
[tex] \frac{5}{R_{2}} =\frac{15}{12} [/tex]
Rā= 4 ohms
Resistance of the circuit is 4 ohms when the current is 15 A.
