Potential and Voltage; Dielectrics and Capacitors
The energy language of the electric field — and the devices that store it
Big Idea: In the previous topic you described the electric field with a force quantity, the field strength E. Here we describe the very same field with an energy quantity: the potential. Potential tells you how much potential energy each coulomb of charge has at a point; the voltage (potential difference) between two points tells you how much work the field does per coulomb as the charge moves between them. A capacitor is then simply a device that stores charge — and electric-field energy — by holding a voltage across a gap.
By the end you will be able to:
- compute the work and potential energy of a charge in a uniform field (W = qEd),
- define potential and potential difference and use W = qU,
- connect voltage and field strength with U = Ed and E = U/d,
- explain what a dielectric does inside a field and what the permittivity ε means,
- define capacitance C = q/U and use the parallel-plate formula,
- find the energy stored in a charged capacitor.