Recall that potential energy is an interaction energy. Charged particles that interact via the electric force have electric potential energy $U_{\text{elec}}$. You’ll learn that there’s a close analogy with gravitational potential energy.

《 LOOKING BACK Section 10.1 Potential energy

《 LOOKING BACK Section 10.5 Energy diagrams

You’ve seen that source charges create an electric field. Source charges also create an electric potential. The electric potential $V$

• Exists everywhere in space.

• Is a scalar.

• Causes charges to have potential energy.

• Is measured in volts.

We’ll calculate the electric potential of four important charge distributions: a point charge, a charged sphere, a ring of charge, and a parallel-plate capacitor. Finding the potential of a continuous charge distribution is similar to calculating electric fields, but easier because potential is a scalar.

《 LOOKING BACK Section 23.3 The electric field

Electric potential is a fairly abstract idea, so it will be important to visualize how the electric potential varies in space. One way of doing so is with equipotential surfaces. These are mathematical surfaces, not physical surfaces, with the same value of the potential $V$ at every point.

A charged particle $q$ in an electric potential $V$ has electric potential energy $U=qV$.

• Charged particles accelerate as they move through a potential difference.

• Mechanical energy is conserved:

《 LOOKING BACK Section 10.4 Energy conservation

Energy allows things to happen. You want your lights to light, your computer to compute, and your music to play. All these require energy—electric energy. This is the first of two chapters that explore electric energy and its connection to electric forces and fields. You’ll then be prepared to understand electric circuits—which are all about how energy is transformed and transferred from sources, such as batteries, to devices that utilize and dissipate the energy.