1. Aim: How do charges have an electric potential difference?
Do Now: Draw the electric field between an electron and a proton right next to each other.
What is the electrostatic force between them if separated by 5x10-6m?
Students put on board!

2. Gravitational Potential!
How is this similar and different for charges?
Where does my ball want to be? What happens if we raise it up? What did I have to do to get it that high in the air?
Use Escalator as an example too!

3. How do we REALLY describe PE?
Earth is the reference point, but really we can pick any point to start from, such as 5 m above Earth on a cliff or even in a hole 5 meters below.
Potential energy is always in reference to some other point, so there is no absolute PE, just a potential difference between two points.
How does this relate to a charge in an E-field?

4. Electric Potential Energy
Where does my electron want to be? How do I separate them? Low PE
High PE - -
Why is PE higher when I pull the two apart? Electric field between two charges
Work done against electric field increases PE
Work done by electric field decreases PE + +

5. Other Examples
Where do I have high Potential Energy and low potential Energy between two positive charges?
Increase Potential Energy!
Do additional examples such as two negative charges!
Allow students to do this on the board! + +

6. Sign Convention for PE + A B
PE has sign convention!
What happens if you drop a ball into a hole?
If the Earth’s surface is taken to be zero PE, then there would be negative PE in the hole!
This applies to Electric Potential energy too!
Calculations should account for potential difference and charge sign!
Ex. A charge at A has 30J of PE ad when released speeds up to point B where it now has -10 J.
It spent all it’s energy, then continued with it’s own internal energy to point B. +
Why is PE higher when I pull the two apart? Electric field between two charges
Work done against electric field increases PE
Work done by electric field decreases PE A B

7. How can we define Electric Potential Difference?
The difference in electric potential between two points.
Measured as the work needed per charge or simply work done on the charge.
How can it be calculated?
We call this “potential difference” voltage.
Voltage is the energy per charge between two pints in space.
PE is the work done to move that charge some distance through space.
Ex. The potential difference between an 8V POSITIVE charge and 6V POSITIVE charge is 2V, but the PE needed to move the 6V charge to that point and stay there is 20J. It would be -20J to move away since it would want to go that way.

8. A 1 Coulomb charge is moved from point A to B.
PE = 30J at B
PE = 20J at A
What is the electric potential at each point for a 2C charge? What is ΔV?
30V
20V
We assume PE is 20 and 30 J at points A and B for both the 1C and 2C cases.
This is a potential difference of 10V

9. Practice 1
27J of work are required to move a Charge of 3C. Determine the voltage. 27 J = 3C x ΔV ΔV = 9 V

10. Practice 2
An electron is accelerated through a potential difference of 150 volts. Calculate the work done on the electron in electronvolts. 1 eV = 1.6 x J *** An eV is a unit for small amounts of energy.
V= 1eV/e = J/C
Answer: 150 V

11. Station Activity
Answer the following questions regarding Charges moving in an E-Field.

12. Station 1
A 4.5μC charge is moved from point A to point B in an Electric field. This requires 7 x 10-4 J of work. What is the potential difference between A and B?

13. Station 2 _ An electron uses 3.2 x 10-19 J to move to a plate.
Which plate does it move to and across how much potential difference?
Does the electron do work if we move it left or right? Why? _ e- +

14. Opposite charges are brought together: Like charges are moved apart:
Identify the following as increase in electrical potential Energy or decrease in electrical potential Energy.
Opposite charges are brought together:
Like charges are moved apart:
Like charges are brought together:
Opposite charges are moved apart:
Decrease
Decrease
Increase
Ask why for each. Who is doing the work? E-Field or Person?
Increase

15. Which has the greater Electric Potential Difference?- + - +

16. Which has the greater Electric Potential Difference- - + +

17. Electric Potential difference in a Uniform Field
What do we know has a uniform electric field?
The electric field intensity between two large, charged, parallel metal plates is 6000 N/c. The plates are 0.05 m apart. What is the electric potential difference between them? e-