Читать книгу Electroanalytical Chemistry - Gary A. Mabbott - Страница 13

In the thought experiment described earlier, a single particle was used as a test charge. The standard definition for electric potential is the energy required to move a unit of positive charge to the position in question. The standard unit of charge in physics is the coulomb and the standard unit of energy is the joule. Electrical energy is measured in volts. One volt represents one joule per coulomb of charge moved.

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The volt is the unit of electric potential energy per unit charge that one normally uses with simple meters in the laboratory. So, whenever someone refers to a voltage at some part of their system, they are describing the electric potential difference between that point and some reference point (usually the ground). The voltage is the number of joules released or spent in moving a coulomb of charge from the reference point to the point in question.

It is important to remember that the potential is the electrical work done per unit charge. However, a coulomb is a rather large amount of charge compared to the charge on a single electron. If moving a coulomb of charge from point A to point B costs 1.00 J of energy, then how much energy is required to move a single positively charged particle between the same points? First, one can calculate charge in coulombs/electron using Faraday's constant, F, the number of coulombs per mole of electrons, 9.6485 x 10⁴ C/mol, together with Avogadro's number.

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This value is the charge on an electron and is known as the elementary charge. One can calculate the energy that would be required to move a single electron through a voltage difference of 1 V by multiplying the elementary charge by 1 V in the units of 1 J/C:

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The result of this calculation is frequently useful and provides the definition for a separate unit of electric potential energy per elementary charge, namely, the electron‐volt, eV.

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