1. Electrical Potential Energy
Section 1 Electric Potential
Chapter 17
Electrical Potential Energy
Electrical potential energy is potential energy associated with a charge due to its position in an electric field.
Electrical potential energy is a component of mechanical energy.
ME = KE + PEgrav + PEelastic + PEelectric

2. Electrical Potential Energy, continued
Section 1 Electric Potential
Chapter 17
Electrical Potential Energy, continued
Electrical potential energy can be associated with a charge in a uniform field.
Electrical Potential Energy in a Uniform Electric Field
PEelectric = –qEd
electrical potential energy = –(charge)  (electric field strength)  (displacement from the reference point in the direction of the field)

3. Electrical Potential Energy
Section 1 Electric Potential
Chapter 17
Electrical Potential Energy

4. Chapter 17 Potential Difference
Section 1 Electric Potential
Chapter 17
Potential Difference
Electric Potential equals the work that must be performed against electric forces to move a charge from a reference point to the point in question, divided by the charge.
The electric potential associated with a charge is the electric energy divided by the charge:

5. Potential Difference, continued
Section 1 Electric Potential
Chapter 17
Potential Difference, continued
Potential Difference equals the work that must be performed against electric forces to move a charge between the two points in question, divided by the charge.
Potential difference is a change in electric potential.

6. Section 1 Electric Potential
Chapter 17
Potential Difference

7. Potential Difference, continued
Section 1 Electric Potential
Chapter 17
Potential Difference, continued
The potential difference in a uniform field varies with the displacement from a reference point.
Potential Difference in a Uniform Electric Field
∆V = –Ed
potential difference = –(magnitude of the electric field  displacement)

8. Chapter 17 Sample Problem Potential Energy and Potential Difference
Section 1 Electric Potential
Chapter 17
Sample Problem
Potential Energy and Potential Difference
A charge moves a distance of 2.0 cm in the direction of a uniform electric field whose magnitude is 215 N/C.As the charge moves, its electrical potential energy decreases by 6.9  J. Find the charge on the moving particle. What is the potential difference between the two locations?

9. Sample Problem, continued
Section 1 Electric Potential
Chapter 17
Sample Problem, continued
Potential Energy and Potential Difference
Given:
∆PEelectric = –6.9  10–19 J
d = m
E = 215 N/C
Unknown:
q = ?
∆V = ?

10. Sample Problem, continued
Section 1 Electric Potential
Chapter 17
Sample Problem, continued
Potential Energy and Potential Difference
Use the equation for the change in electrical potential energy.
PEelectric = –qEd
Rearrange to solve for q, and insert values.

11. Sample Problem, continued
Section 1 Electric Potential
Chapter 17
Sample Problem, continued
Potential Energy and Potential Difference
The potential difference is the magnitude of E times the displacement.

12. Potential Difference, continued
Section 1 Electric Potential
Chapter 17
Potential Difference, continued
At right, the electric poten-tial at point A depends on the charge at point B and the distance r.
An electric potential exists at some point in an electric field regardless of whether there is a charge at that point.

13. Potential Difference, continued
Section 1 Electric Potential
Chapter 17
Potential Difference, continued
The reference point for potential difference near a point charge is often at infinity.
Potential Difference Between a Point at Infinity and a Point Near a Point Charge
The superposition principle can be used to calculate the electric potential for a group of charges.

14. Superposition Principle and Electric Potential
Section 1 Electric Potential
Chapter 17
Superposition Principle and Electric Potential

15. Capacitors and Charge Storage
Section 2 Capacitance
Chapter 17
Capacitors and Charge Storage
A capacitor is a device that is used to store electrical potential energy.
Capacitance is the ability of a conductor to store energy in the form of electrically separated charges.
The SI units for capacitance is the farad, F, which equals a coulomb per volt (C/V)

16. Capacitors and Charge Storage, continued
Section 2 Capacitance
Chapter 17
Capacitors and Charge Storage, continued
Capacitance is the ratio of charge to potential difference.

17. Section 2 Capacitance
Chapter 17
Capacitance

18. Capacitors and Charge Storage, continued
Section 2 Capacitance
Chapter 17
Capacitors and Charge Storage, continued
Capacitance depends on the size and shape of a capacitor.
Capacitance for a Parallel-Plate Capacitor in a Vacuum

19. Capacitors and Charge Storage, continued
Section 2 Capacitance
Chapter 17
Capacitors and Charge Storage, continued
The material between a capacitor’s plates can change its capacitance.
The effect of a dielectric is to reduce the strength of the electric field in a capacitor.

20. Capacitors in Keyboards
Section 2 Capacitance
Chapter 17
Capacitors in Keyboards

21. Parallel-Plate Capacitor
Section 2 Capacitance
Chapter 17
Parallel-Plate Capacitor

22. Chapter 17 Energy and Capacitors
Section 2 Capacitance
Chapter 17
Energy and Capacitors
The potential energy stored in a charged capacitor depends on the charge and the potential difference between the capacitor’s two plates.

23. Chapter 17 Sample Problem Capacitance
Section 2 Capacitance
Chapter 17
Sample Problem
Capacitance
A capacitor, connected to a 12 V battery, holds 36 µC of charge on each plate. What is the capacitance of the capacitor? How much electrical potential energy is stored in the capacitor?
Given:
Q = 36 µC = 3.6  10–5 C
∆V = 12 V
Unknown:
C = ? PEelectric = ?

24. Sample Problem, continued
Section 2 Capacitance
Chapter 17
Sample Problem, continued
Capacitance
To determine the capacitance, use the definition of capacitance.

25. Sample Problem, continued
Section 2 Capacitance
Chapter 17
Sample Problem, continued
Capacitance
To determine the potential energy, use the alternative form of the equation for the potential energy of a charged capacitor:

26. Current and Charge Movement
Section 3 Current and Resistance
Chapter 17
Current and Charge Movement
Electric current is the rate at which electric charges pass through a given area.

27. Section 3 Current and Resistance
Chapter 17
Conventional Current

28. Chapter 17 Drift Velocity
Section 3 Current and Resistance
Chapter 17
Drift Velocity
Drift velocity is the the net velocity of a charge carrier moving in an electric field.
Drift speeds are relatively small because of the many collisions that occur when an electron moves through a conductor.

29. Section 3 Current and Resistance
Chapter 17
Drift Velocity

30. Chapter 17 Resistance to Current
Section 3 Current and Resistance
Chapter 17
Resistance to Current
Resistance is the opposition presented to electric current by a material or device.
The SI units for resistance is the ohm (Ω) and is equal to one volt per ampere.
Resistance

31. Resistance to Current, continued
Section 3 Current and Resistance
Chapter 17
Resistance to Current, continued
For many materials resistance is constant over a range of potential differences. These materials obey Ohm’s Law and are called ohmic materials.
Ohm’s low does not hold for all materials. Such materials are called non-ohmic.
Resistance depends on length, cross-sectional area, temperature, and material.

32. Factors that Affect Resistance
Section 3 Current and Resistance
Chapter 17
Factors that Affect Resistance

33. Resistance to Current, continued
Section 3 Current and Resistance
Chapter 17
Resistance to Current, continued
Resistors can be used to control the amount of current in a conductor.
Salt water and perspiration lower the body's resistance.
Potentiometers have variable resistance.

34. Sources and Types of Current
Section 4 Electric Power
Chapter 17
Sources and Types of Current
Batteries and generators supply energy to charge carriers.
Current can be direct or alternating.
In direct current, charges move in a single direction.
In alternating current, the direction of charge movement continually alternates.

35. Electric power = current  potential difference
Section 4 Electric Power
Chapter 17
Energy Transfer
Electric power is the rate of conversion of electrical energy.
Electric power
P = I∆V
Electric power = current  potential difference

36. Section 4 Electric Power
Chapter 17
Energy Transfer

37. Energy Transfer, continued
Section 4 Electric Power
Chapter 17
Energy Transfer, continued
Power dissipated by a resistor
Electric companies measure energy consumed in kilowatt-hours.
Electrical energy is transferred at high potential differences to minimize energy loss.

38. Relating Kilowatt-Hours to Joules
Section 4 Electric Power
Chapter 17
Relating Kilowatt-Hours to Joules