1. Chapter 17
Section 1 Electric Potential
Objectives
Distinguish between electrical potential energy, electric potential, and potential difference.
Solve problems involving electrical energy and potential difference.
Describe the energy conversions that occur in a battery.

2. Electrical Potential Energy
Chapter 17
Section 1 Electric Potential
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

3. Electrical Potential Energy, continued
Chapter 17
Section 1 Electric Potential
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)

4. Chapter 17 Potential Difference
Section 1 Electric Potential
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
Chapter 17
Section 1 Electric Potential
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. Potential Difference, continued
Chapter 17
Section 1 Electric Potential
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)

7. Chapter 17 Sample Problem Potential Energy and Potential Difference
Section 1 Electric Potential
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?

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

9. Sample Problem, continued
Chapter 17
Section 1 Electric Potential
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.

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

11. Potential Difference, continued
Chapter 17
Section 1 Electric Potential
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.

12. Potential Difference, continued
Chapter 17
Section 1 Electric Potential
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.

13. Chapter 17
Section 2 Capacitance
Objectives
Relate capacitance to the storage of electrical potential energy in the form of separated charges.
Calculate the capacitance of various devices.
Calculate the energy stored in a capacitor.

14. Capacitors and Charge Storage
Chapter 17
Section 2 Capacitance
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)

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

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

17. Capacitors and Charge Storage, continued
Chapter 17
Section 2 Capacitance
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.

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

19. Chapter 17 Energy and Capacitors
Section 2 Capacitance
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.

20. Chapter 17 Sample Problem Capacitance
Section 2 Capacitance
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 = ?

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

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

23. Section 3 Current and Resistance
Chapter 17
Objectives
Describe the basic properties of electric current, and solve problems relating current, charge, and time.
Distinguish between the drift speed of a charge carrier and the average speed of the charge carrier between collisions.
Calculate resistance, current, and potential difference by using the definition of resistance.
Distinguish between ohmic and non-ohmic materials, and learn what factors affect resistance.

24. 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.

25. 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.

26. 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

27. 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.

28. 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.

29. Chapter 17
Section 4 Electric Power
Objectives
Differentiate between direct current and alternating current.
Relate electric power to the rate at which electrical energy is converted to other forms of energy.
Calculate electric power and the cost of running electrical appliances.

30. Sources and Types of Current
Chapter 17
Section 4 Electric Power
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.

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

32. Energy Transfer, continued
Chapter 17
Section 4 Electric Power
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.