電位

Electric potential (φ) is the electrical potential energy per unit charge at a specific point in an electric field, measured in volts. Voltage is the potential difference between two points in the field. While both are measured in volts, voltage specifically represents the difference between two potentials, such as between a battery's positive and negative terminals.

Electric potential magnitude depends on three factors: the source charge Q producing the electric field, the distance d from the source charge, and the configuration of the charge. For a point charge or uniformly charged sphere, potential is inversely proportional to distance, meaning it decreases as you move farther from the charged object.

Equipotential surfaces are regions where all points have the same electric potential. Around a charged sphere, these surfaces are spherical because all locations at the same radius from the sphere's center experience identical potential values. The potential depends only on distance, not on angular position around the sphere.

The sign of electric potential depends on the source charge creating the field. Around an isolated positive charge, the potential is positive, while around an isolated negative charge, the potential is negative. This sign convention helps identify whether work must be done against or with the field to move a test charge.

Using a Van der Graff generator to charge a metal sphere and a voltmeter with a probe, measure potential at different distances from the sphere's center. Keeping the probe at constant radius shows equipotential surfaces with constant readings. Plotting measured potential versus distance reveals an inverse relationship, validating theoretical predictions.

Electric potential energy is the work required to move a test charge from a reference point to a specific location in an electric field. Electric potential is this energy divided by the charge, giving energy per unit charge. Both depend on the source charge and distance, but potential is a field property independent of the test charge used.

In gel electrophoresis, an electric potential difference applied across agarose gel separates DNA and molecules by size and charge as they move through the electric field. In electron microscopy, high electric potential differences accelerate electrons in a beam that bombards samples, providing much greater spatial resolution than optical microscopes due to smaller wavelengths.