1. Section 1 Electric Potential
Chapter 17
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
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

3. 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)

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.

7. PEelectric = −qEd .

8. 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)

9. . . .

10. 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.

11. 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.

12. Chapter 17 . Potential Energy and Potential Difference
Section 1 Electric Potential
Chapter 17 .
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?

13. 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 = ?

14. 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.

15. 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.

16. 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.

17. 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.

19. 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.

20. 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

21. 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.

22. Ohm’s low does not hold for all materials
Ohm’s low does not hold for all materials. Such materials are called non-ohmic.

23. Factors That Affect Resistance
Section 2 Capacitance
Chapter 17
Factors That Affect Resistance

24. 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.
Human body resistance to current (Dry skin)=
Ohm. (soaked with water=100 Ohm)
Currents less than 0.01 imperceptible (or slight tingling)
Currents greater than 0.15 disrupt electrical activity of heart (can be fatal).
Potentiometers have variable resistance. (Knobs, dimmers…)

26. Section 4 Electric Power
Chapter 17
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.

27. 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.

28. Current can be direct or alternating.

30. 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

31. Section 4 Electric Power
Chapter 17
Energy Transfer

32. 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.

35. Electrical energy is transferred at high potential differences to minimize energy loss