# A charge of 6 C passes through a circuit every 3 s. If the circuit can generate 72 W of power, what is the circuit's resistance?

Jun 3, 2017

The resistance is $= 18 \Omega$

#### Explanation:

We apply the equation

$Q = I t$

The charge is $Q = 6 C$

The time is $t = 3 s$

The current is $I = \frac{Q}{t} = \frac{6}{3} = 2 A$

The power is

$P = U I$

But according to Ohm's Law

$U = R I$

So,

$P = R I \cdot I = R {I}^{2}$

So,

the resistance is $R = \frac{P}{I} ^ 2$

$= \frac{72}{2} ^ 2 = 18 \Omega$