1. Electric Potential Difference Or Voltage
Forces and Fields 8

2. Consider a mass positioned in a gravitational field
1.0kg
2.00m
A mass above a reference level (ground) possesses gravitational potential energy.
Work must be done against the force of gravity to increase Ep. (Lifting the object further off the ground increases Ep)
Between the two points in the gravitational field above the ground,(2m and 5m) the difference in Ep can be determined.

3. Consider a charge placed within an electric field
Electric Potential Energy
- charge - d
+ charge - d
moving the – charge away from the positive charge requires work which increases electric potential energy and moving the – charge toward the negative charge also does the same

4. Electrical Ep changes when work is done in moving a charge from one point to another within an electric field
Ep lesser
Ep greater
-q1 + + d
To increase Ep between two unlike charges, move them farther apart. d + - d + -
Low Ep
Higher Ep

5. To increase electric Ep between two like charges, move them closer together+ d + d
Low Ep
Higher Ep
Electrical Potential Difference or Voltage (V)
the ratio of the change in energy (work, potential or kinetic) per unit charge (1.00 C) within an electrical field

6. Eg) two oppositely charged plates+
+ + -
uniform
High Ep
low Ep
Between the two points that a positive charge has moved within the electric field, there exists a voltage

7. Electric potential difference or voltage is the change in potential energy per unit charge.
Equation:
In Joules
In Coulombs
The ratio of E/q is called a volt and is named after Alex Volta who invented the battery

8. Examples:
A 12.0 volt battery supplies 12.0 joules of energy to move a C charge through a circuit.
The voltage of 1.00 V between two points in an electric field means that 1.00 J of energy is needed to move a 1.00 C charge between the two points in the field.

9. +
+ + -
1.00 V

10. Example:
A charge of X 10-3uC is moved from a positive plate to a negative plate by doing 1.17 X 10-5 J of work. What is the potential difference between the plates? +
+ + -

11. 2nd Equation for Voltage
The potential difference or voltage between two oppositely charged plates is determined by the magnitude of the uniform electric field, E, and the distance between the plates.
Equation for voltage between oppositely charged plates:
Work, Ep
or Ek, energy

12. Example:
Determine the electric field strength between 2 oppositely charged plates 25 cm apart to which 120 V is supplied. +
+ + -
V = 120 v
0.25 m