32.6 Power in AC Circuits

A primary role of the emf is to supply energy. Some circuit devices, such as motors and lightbulbs, use the energy to perform useful tasks. Other circuit devices dissipate the energy as an increased thermal energy in the components and the surrounding air. Chapter 28 examined the topic of power in DC circuits. Now we can perform a similar analysis for AC circuits.

The emf supplies energy to a circuit at the rate

where $i$ and $\epsilon$ are the instantaneous current from and potential difference across the emf. We’ve used a lowercase $p$ to indicate that this is the instantaneous power. We need to look at the energy losses in individual circuit elements.