1. January 23-26 2015

2. Electrical Potential Energy Just as masses can have gravitational potential energy, charges can have electrical potential energy E Electrical potential energy A mass gains PE g if work is done against gravity (i.e., if the mass is moved against the gravitational field) A charge gains PE e if work is done against electric force (e.g., if the positive charge is moved against the electric field)

3. Electrical Potential Energy How can a charge (or mass) gain potential energy? By changing location. Gravitational potential energy Electrical potential energy Low PE High PE Work done by monkey Work done by electricity

4. Electrical Potential Energy & Charge Does the amount of work done by the monkey change if the charge changes? How do we know? What does this imply about potential energy? Potential energy depends on both location and charge.

5. Electrical Potential Energy & Electrical Potential Introducing … Electrical Potential (V) … a measure that depends only on location, not on charge. Two different things that sound alike! The SI unit of electric potential is the volt.

6. + + + + + + + + + + + + + + + + + + + + + + + + + + + + Electrical Potential Energy vs Electrical Potential 0.5 m A B Two positive charges, A and B, are placed at equal distances from a positively charged sphere. A has a larger charge than B.

7. + + + + + + + + + + + + + + + + + + + + + + + + + + + + Electrical Potential Energy vs Electrical Potential 0.5 m A B Two positive charges, A and B, are placed at equal distances from a positively charged sphere. A has a larger charge than B. Which has greater potential energy (PE)? 1) A 2) B 3) They have the same PE Which has greater electrical potential (V)? 1) A 2) B 3) They have the same V

8. + + + + + + + + + + + + + + + + + + + + + + + + + + + + Electrical Potential Energy vs Electrical Potential 0.5 m A B Two positive charges, A and B, are placed at equal distances from a positively charged sphere. A has a larger charge than B. Which has greater potential energy (PE)? 1) A 2) B 3) They have the same PE Which has greater electrical potential (V)? 1) A 2) B 3) They have the same V

9. + + + + + + + + + + + + + + + + + + + + + + + + + + + + Electrical Potential Energy vs Electrical Potential 0.5 m A B Note important difference between energy and potential: Note important difference between energy and potential: A point has potential, charge placed there has electric potential energy A point has potential, charge placed there has electric potential energy Two points that are at the same distance from the charged object have the same potential. So, when two charged objects are placed there, they are at the same potential, but the one with more charge on it has higher electric potential energy. It is harder to push it there.

10. Electrical Potential Energy vs Electrical Potential The quantity electric potential is defined as the amount of _____. 1. electric potential energy 2. force acting upon a charge 3. potential energy per charge 4. force per charge

11. Electrical Potential Energy vs Electrical Potential The quantity electric potential is defined as the amount of _____. 1. electric potential energy 2. force acting upon a charge 3. potential energy per charge 4. force per charge

12. Electrical Potential Energy vs Electrical Potential What happens if a positive charge is moved from point A to point B?

13. Electrical Potential Energy vs Electrical Potential What happens if a positive charge is moved from point A to point B?

14. Potential Difference (ΔV) Charge will naturally move from areas of high potential to areas of low potential. Work / an input of energy is needed to move charge up from low potential to high

15. What is the role of a battery in a circuit? Potential Difference (ΔV) & Circuits Batteries supply energy to maintain a potential difference across the circuit.

16. What is the role of a battery in a circuit? Potential Difference (ΔV) & Circuits Batteries supply energy to maintain a potential difference across the circuit. 1)A 12V battery means that the + terminal has an electric potential that is 12V higher than the – terminal.

17. What is the role of a battery in a circuit? Potential Difference (ΔV) & Circuits Batteries supply energy to maintain a potential difference across the circuit. 1)A 12V battery means that the + terminal has an electric potential that is 12V higher than the – terminal. 2)Charges flow through the external circuit (the wire) from high to low potential.

18. What is the role of a battery in a circuit? Potential Difference (ΔV) & Circuits Batteries supply energy to maintain a potential difference across the circuit. 1)A 12V battery means that the + terminal has an electric potential that is 12V higher than the – terminal. 2)Charges flow through the external circuit (the wire) from high to low potential. 3)As the charges flow through the circuit, they ‘lose’ energy to circuit elements such as lights and motors

19. What is the role of a battery in a circuit? Potential Difference (ΔV) & Circuits Batteries supply energy to maintain a potential difference across the circuit. 1)A 12V battery means that the + terminal has an electric potential that is 12V higher than the – terminal. 2)Charges flow through the external circuit (the wire) from high to low potential. 3)As the charges flow through the circuit, they ‘lose’ energy to circuit elements such as lights and motors 4)By the time the charges get to the end terminal, they have used up 12 V of potential

20. What is the role of a battery in a circuit? Potential Difference (ΔV) & Circuits Batteries supply energy to maintain a potential difference across the circuit. 1)A 12V battery means that the + terminal has an electric potential that is 12V higher than the – terminal. 2)Charges flow through the external circuit (the wire) from high to low potential. 3)As the charges flow through the circuit, they ‘lose’ energy to circuit elements such as lights and motors 4)By the time the charges get to the end terminal, they have used up 12 V of potential 5)The battery supplies the energy necessary to ‘push’ the charges back to high potential

21. Potential Difference (ΔV) & Circuits As charges ‘lose’ energy to different circuit elements, the electric potential decreases. This is known as voltage drop. All of the electric potential difference– i.e. all of the voltage -- is used up by the end of the circuit.

22. 1.The variable we use for potential, potential difference, and the unit for potential difference (volts) is V. 2.Don't let that confuse you when you see V = 1.5V 3.Electric potential energy is not the same as electrical potential. 4.The electron volt is not a smaller unit of the volt, it's a smaller unit of the Joule. 5.Electrical potential can also be described by the terms, potential difference, voltage, voltage drop, potential drop, potential rise, electromotive force, and EMF. These terms may differ slightly in meaning depending on the situation.

23. Check your understanding Compare an electric circuit to a roller coaster ride. What is the difference in height from the top to the bottom of a rollercoaster analogous to in a circuit? What is the motor that pulls the rollercoaster up the hill analogous to in circuit?

24. Check your understanding Compare an electric circuit to a roller coaster ride. What is the difference in height from the top to the bottom of a rollercoaster analogous to in a circuit? potential difference What is the motor that pulls the rollercoaster up the hill analogous to in circuit? battery

25. If a battery provides a high voltage, it can ____. 1.do a lot of work over the course of its lifetime 2.do a lot of work on each charge it encounters 3.push a lot of charge through a circuit 4.last a long time Check your understanding

26. If a battery provides a high voltage, it can ____. 1.do a lot of work over the course of its lifetime 2.do a lot of work on each charge it encounters 3.push a lot of charge through a circuit 4.last a long time Check your understanding

27. Compared to point D, point A has … 1.12 V higher potential energy 2.12 V lower potential energy 3.Exactly the same potential energy The electrical potential energy is 0 at … 1.A 2.B 3.C 4.D

28. Check your understanding Compared to point D, point A has … 1.12 V higher potential energy 2.12 V lower potential energy 3.Exactly the same potential energy The electrical potential energy is 0 at … 1.A 2.B 3.C 4.D

29. Check your understanding Energy is required to move a charge from… 1.Point A to point B 2.Point B to point C 3.Point C to point D 4.Point D to point A The energy required to move +2C of charge from D to A is 1. 0.167 J 2. 2 J 3. 6 J 4. 24 J

30. Check your understanding Energy is required to move a charge from… 1.Point A to point B 2.Point B to point C 3.Point C to point D 4.Point D to point A The energy required to move +2C of charge from D to A is 1. 0.167 J 2. 2 J 3. 6 J 4. 24 J