Aim: How do we explain electric potential difference (or Voltage)?

At which point will a test charge have more electric PE? Why? B

Gravitational Potential Energy

Electric Potential Difference The Electric Potential Difference between two points (A and B) in an electric field is defined as the work done per charge in moving a charge from point A to point B in an electric field. V = W/q V= Potential Difference (Measured in Volts) W= Work (Measured in Joules) q= charge (Measured in Coulombs)

Electric Potential Electric Potential can be thought of as the electrical potential energy per unit charge. Compare with gravity

Electric Potential Difference in Electric Fields

Potential Difference = Voltage The Potential Difference between two points in an electric field can be thought of as the differences in electric potential between the two points. (Duh) Potential Difference is the same thing as voltage.

Example 1 a) 18 J of work are required to move 2.0 C of charge between two points in an electric field. Find the electric potential difference between the two points. V=W/q=18J/2C=9V b) How much work would be required to move 4.0 C of charge between the same two points of the problem above? V=W/q 9V=W/4C W=36 J

Example 2 What is the electric potential difference between two points in an electric field if it requires 100 J to move 4 C of charge from one of the points to the other? V=W/q=100J/4C=5V

Example 3 A potential difference of 12 V exists between points A and B. How much work would be required to move 36 Coulombs of charge from A to B? V=W/q 12V=W/36 C W=432J

Example 4 Moving 4 Coulombs of charge through a circuit requires 48 joules of electric energy. What is the potential difference across this circuit? 190 V 48 V 12 V 4 V

Example 5 How much work is required to move 3.0 coulombs of electric charge a distance of 0.010 meter through a potential difference of 9.0 volts? a) 2.7 x 103 J b) 27 J c) 3.0 J d) 3.0 x 10-2 J

Sources of Potential Difference or Voltage

Equilibrium Condition Charges will flow between two conductors until both conductors have the same electric potential

Significance of electric potential difference When there is a potential difference between two points, a current will flow.

Electron-volts An electronvolt is the work required to move 1 electron through 1 volt of potential difference. Electronvolts measure work and energy. 1 ev = 1.6 x 10-19 J

Conversions Ex. Convert 9.6 x 10-19 J to eV. Ex. Convert 4640 eV to J

Example 4 20 electronvolts of work are required to move 8 electrons between two points in an electric field. Find the electric potential difference between the two points

Example 5 a) How much work (in eV) is done on a proton when it is accelerated through a potential difference of 68,000 volts? b) How much kinetic energy is gained by the proton?

Example 6 Find the work done in joules in moving 5 electrons through a potential difference of 6.0 V.