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Work must be done to move oppositely charged particles apart. Conversely, work must be done to move either two positively charged particles or two negatively charged particles closer together. Electric potential energy is the work required to move a charged particle in an electric field. The unit for electric potential energy is joules.
Electric potential energy is the energy required to move a particle to a point in an electric field from a point infinitely far away. By definition, the electric potential energy of a charge separated from another charge by infinity is zero.
Electric potential is electric potential energy per unit of charge. If a particle has twice the charge, then twice the work is required to move the particle in an electric field. In other words, the electric potential energy is twice as great when moving a particle that has twice the charge. However, the electric potential energy for each unit of charge is the same. The unit for electric potential is joules per coulombs, also known as volts.
Different points in an electric field or in an electric circuit may have different electric potential. Potential difference is the difference in electric potential between different points in a circuit or in a field. Since potential difference is the difference between electric potential energies, its unit is joules per coulomb, or volts.
As a particle falls through an electric field, kinetic energy increases as electric potential energy decreases, increasing the speed of the particle. As a particle moves in an electric circuit, the electric potential energy may be converted to heat, or useful work or some combination of both. Therefore, in practical terms, potential difference is the work available per unit charge.
EMF is the maximum potential difference generated by a voltage source in a closed electric circuit. EMF is not a force; it is the available work per unit charge (joules per coulomb, or volts) for the entire circuit.
Consider a charged particle in an electric field. If the particle had twice the charge, which of the following statements would be true?
a. The electric potential energy and the electric potential would both be twice as great.
b. The electric potential energy would be twice as great and the electric potential would be the same.
c. The electric potential energy would be the same and the electric potential would be twice as great.
d. The electric potential energy and the electric potential would both be the same.