If there is a strong enough electric field, sparks form in the air where the electricity jumps from one object to another. In this chapter, we discuss electrical energy and electric potential.
- The electric field between two parallel-plate conductors is considered uniform far away from the plate edges if the size of the plates is large compared to their separation distance.
- The potential energy of a charge q at a point between two parallel-plate conductors is PE=qEx, a reference point must be given such as PE=0 at x=0.
- A point charge q has electric potential energy PEx and electric potential Vx at point x. Thus, PEx=qVx
- The word voltage is used when we mean potential difference.
- It is common to write V=Ed, where V is understood to mean the voltage (or potential difference) between the plates of a parallel-plate conductor and d is the distance between the plates.
- The work done by the electric field in moving a charge between two parallel plate conductors is Wfield=−qΔV. The work done by an external force is Wexternal force=qΔV.
- Voltage can be thought of as the work per unit charge V=Wq; that is, how much work is required per unit charge to move a charged particle in an electric field.
- Capacitance of an air-gap capacitor is given by C=ε0Ad where A is the area of the capacitor and d is the separation distance between the plates.
- The charge on a capacitor is directly proportional to the voltage of the capacitor Q=CV.
- A dielectric material placed between the plates increases the capacitance of the capacitor. The capacitance of a capacitor with a dielectric is expressed as C=kε0Ad, where k is the dielectric constant.
- The energy stored in a capacitor can be expressed as