Question: In what way are potentials used?
About the article "Thermodynamics", section "Potentials".

Candidate passages:
Since gradients in potentials correspond to physical fields, it makes no difference if a constant is added on (it is erased by the gradient operator which includes partial differentiation).
This means there is no way to tell what the "absolute value" of the potential "is" - the zero value of potential is completely arbitrary and can be chosen anywhere by convenience (even "at infinity").
This idea also applies to vector potentials, and is exploited in classical field theory and also gauge field theory.
Absolute values of potentials are not physically observable, only gradients are.
However, the Aharonov–Bohm effect is a quantum mechanical effect which illustrates that non-zero electromagnetic potentials (even when the and fields are zero) lead to changes in the phase of the wavefunction of an electrically charged particle, so the potentials appear to have measurable significance. 
Spike potentials are one of the action potentials, which occur in electrical activity of smooth muscle contraction in animals.
These are true action potentials. 
In advanced classical mechanics it is often useful, and in quantum mechanics frequently essential, to express Maxwell's equations in a "potential formulation" involving the electric potential (also called scalar potential) φ, and the magnetic potential (also called vector potential) A.
For example, the analysis of radio antennas makes full use of Maxwell's vector and scalar potentials to separate the variables, a common technique used in formulating the solutions of differential equations.
The potentials can be introduced by using the Poincaré lemma on the homogeneous equations to solve them in a universal way (this assumes that we consider a topologically simple, e.g.
contractible space).
The potentials are defined as in the table above.
Alternatively, these equations define E and B in terms of the electric and magnetic potentials which then satisfy the homogeneous equations for E and B as identities.
Substitution gives the non-homogeneous Maxwell equations in potential form.
Many different choices of A and φ are consistent with given observable electric and magnetic fields E and B, so the potentials seem to contain more, (classically) unobservable information.
The non uniqueness of the potentials is well understood, however.
For every scalar function of position and time λ("x", "t"), the potentials can be changed by a gauge transformation as  formula_60 without changing the electric and magnetic field.
Two pairs of gauge transformed potentials (φ, A) and (φ′, A′) are called gauge equivalent, and the freedom to select any pair of potentials in its gauge equivalence class is called gauge freedom.
Again by the Poincaré lemma (and under its assumptions), gauge freedom is the only source of indeterminacy, so the field formulation is equivalent to the potential formulation if we consider the potential equations as equations for gauge equivalence classes.
The potential equations can be simplified using a procedure called gauge fixing.
Since the potentials are only defined up to gauge equivalence, we are free to impose additional equations on the potentials, as long as for every pair of potentials there is a gauge equivalent pair that satisfies the additional equations (i.e.
if the gauge fixing equations define a slice to the gauge action).
The gauge-fixed potentials still have a gauge freedom under all gauge transformations that leave the gauge fixing equations invariant.
Inspection of the potential equations suggests two natural choices.
In the Coulomb gauge, we impose formula_61 which is mostly used in the case of magneto statics when we can neglect the "c"−2∂2A/∂"t"2 term.
In the Lorenz gauge (named after the Dane Ludvig Lorenz), we impose  formula_62 The Lorenz gauge condition has the advantage of being Lorentz invariant and leading to Lorentz-invariant equations for the potentials.  
Fortunately, there is a way to simplify these equations that takes advantage of the fact that the potential fields are not what is observed, the electric and magnetic fields are.
Thus there is a freedom to impose conditions on the potentials so long as whatever condition is chosen to impose does not affect the resultant electric and magnetic fields.
This freedom is called gauge freedom.
Specifically for these equations, for any choice of a scalar function of position and time λ, the potentials can be changed as follows: formula_4 formula_5 This freedom can be used to greatly simplify the potential formulation.
Generally, two such scalar functions are chosen. 
A successful way of describing nuclear interactions is to construct one potential for the whole nucleus instead of considering all its nucleon components.
This is called the "macroscopic" approach.
For example, scattering of neutrons from nuclei can be described by considering a plane wave in the potential of the nucleus, which comprises a real part and an imaginary part.
This model is often called the optical model since it resembles the case of light scattered by an opaque glass sphere.
Nuclear potentials can be "local" or "global": local potentials are limited to a narrow energy range and/or a narrow nuclear mass range, while global potentials, which have more parameters and are usually less accurate, are functions of the energy and the nuclear mass and can therefore be used in a wider range of applications.