Question

a circut contains two devices that are connected in parallel if the resistance of one of these devices is 12 ohms and the resistance of the other device is 4ohms, the total resistance of the two devices is?

Answer 1

Answer: $3\Omega$

Explanation:

When devices $n$ are connected in parallel, the total resistance  $R$ is calculated by:

$\frac{1}{R}=\frac{1}{R_{1}}+\frac{1}{R_{2}}+...+\frac{1}{R_{n}}$

In this case we have 2 devices connected in parallel, and their resistances are

$R_{1}=12\Omega$ and $R_{2}=4\Omega$. Therefore:

$\frac{1}{R}=\frac{1}{R_{1}}+\frac{1}{R_{2}}$

$\frac{1}{R}=\frac{1}{12\Omega}+\frac{1}{4\Omega}$

$\frac{1}{R}=\frac{1}{3\Omega}$

Finally:

$R=3\Omega$  This is the total resistance of the two devices