Six Chapter Three

Electric Potential

• There is a similarity in form between the equations for gravity and the equations for electric charges

• Since the form of the force equations are similar, then a similar method as for gravity can be used to get an equation for electric potential energy.
• If Q and q are opposite, then E_e is negative and the charges attract just as with gravity. As a result, energy is stored by separating charges.
• If Q and q are the same, then E_e is positive and the charges repel. As a result, energy is stored by moving charges closer together.

• In both cases (Q & q oppositely charged or like charged), E_e = 0 when r is infinite
• Electric potential energy depends upon the magnitude of the charge on each charged object.
• Sometimes it is useful to have a quantity that is dependent on the charge on only one object.
• Electric potential - The potential energy per unit positive charge.
  • The work done per unit positive charge to move the charge from infinity to any given point.

• Electric potential is a property of the electric field of the charge.
• V in the above equation is electric potential
• The unit of electric potential is the volt.

1 Volt = 1 J/C = 1 V

• 1 Volt - The electric potential at a point in an electric field if 1 J of work is required to move 1 C of charge from infinity to that point.
• If there is more than one electric charge present, then the definition of electric potential is unchanged.
• More commonly, we think in terms of moving a test charge from one place to another in a field.
  • Under these circumstances, we talk about the change in electric potential
• Potential difference - The difference in potential energy per unit of positive charge between two places in a field. Potential difference some times referred to as:
  • Change in electric potential
  • Voltage difference

• Electric potential is the work required to move 1 C of charge from one place to another in an electric field. It would be the work to move the charge from A to B below
• Mathematically, the equation becomes:

• Potential difference decreases for positive charges in the direction of the field, and increases in the opposite direction.
• Potential difference increases for negative charges in the direction of the field, and decreases in the opposite direction
• For a uniform electric field (as between parallel plates) work is required to move a charge from place to place.

December 18, 2013