Electric Potential Difference (SL IB Physics)

• Potential difference (p.d.) is a measure of the electrical potential energy transferred by electrons as they move between two points in a conductor
• The definition of potential difference, also known as voltage, is:

The work done per unit charge on moving a positive charge between two points along the path of the current

• Potential difference is measured in volts (V) and is calculated as follows:

• Where:
  • V = potential difference (V)
  • W = work done (J)
  • q = charge (C)

• From the above equation, one volt is equal to one joule per unit coulomb
  • 1 V = 1 J C^–1

• The potential difference in a d.c. circuit is provided by cells or batteries
  • Each cell has a positive terminal (high potential location) and a negative terminal (low potential location)
  • A battery is a collection of cells arranged positive terminal to negative terminal

A cell and a battery made of three cells

• When both terminals of a cell, or battery, are connected to a loop of conducting wire, a circuit is formed
• The cell or battery is the source of the potential difference needed for the electrons to flow
• Electrons gain electrical potential energy as they move through the cell 
  • A small amount of their energy is transferred to the metal ions in the wire
  • The flow of electrons is from the negative to the positive terminal

The Electronvolt

• The energy values associated to electrons and other microscopic particles are very small when expressed in SI units
• For this reason, it is often more convenient to use another unit for energy - the electronvolt (eV)
• The electronvolt is defined as follows:

The amount of energy needed to move an electron through a potential difference of one volt