To define volt

Under the action of a battery, charges of opposite sign move in opposite directions and so a convention for current direction has to be chosen.

One coulomb (C) is the quantity of electric charge carried past a given point in a circuit when a steady current of 1 ampere flows for 1 second.

If a steady current I (in amperes) flows for time t (in seconds) then the quantity Q (in coulombs) of charge that passes is given by: Q=It

The charge on an electron is 1.60 X 10^-19 C

Consider a conductor of length I and cross-section area A having n ‘free’ electrons per unit volume each carrying a charge e:

Volume of conductor = Al

Number of ‘free’ electrons = nAl

Total charge Q of ‘free’ electron = nAle

I = Q/t = nAle/t

Drift velocity, v = l/t, therefore t = l/v

I = nAle/(l/v) = nAev

v = l/nAe

The potential different V between two points in a circuit is the amount of electrical energy transformed into other forms of energy when unit charge passes from one point to the other.

The unit of potential difference is the volt (V) and equals the p.d. between two points in a circuit in which 1 joule of electrical energy is transformed when 1 coulomb passes from one point to the other.

If a charge of Q (in coulombs) flows in a part of a circuit across which there is a p.d. of V (in volts) then the energy charge W (in joules) is given by: W = QV

W = ItV

Duncan, T. (2003). Advanced Physics For Hong Kong. London: John Murray (Publishers) Ltd.

In physics, the electron-volt is a unit of energy equal to 1.6×10⁻¹⁹ J. By definition, it is the amount of energy gained (or lost) by the charge of a single electron moving across an electric potential difference of one volt.

(en.wikipedia.org)