Alternating Current: Practice Problem & Solution

Solution Explained:

To solve this problem, we apply the core principles of Alternating Current. Understanding the underlying formula is key to arriving at the correct answer below:

The applied voltage is $V = \sqrt{V_R^2 + (V_L - V_C)^2}$.
Substituting values, $V = \sqrt{80^2 + (100 - 40)^2} = \sqrt{6400 + 3600} = 100 V$.
The power factor is $\cos\phi = \frac{V_R}{V}$.
$\cos\phi = \frac{80}{100} = 0.8$.