1. Current Electric Current (I)
The rate at which charge flows through a perpendicular surface
C/s or Ampere, A
The current has the same direction as the flow of positive charge.

2. Current Direct Current (DC) Alternating Current (AC)
The constant current in magnitude and direction
Alternating Current (AC)
The current changing in magnitude and direction all the time

3. Current vd : drift speed of charge q
n : number of mobile charge carriers per unit volume

4. Quiz #1
Consider positive and negative charges moving horizontally through the four regions shown in the figure. Rank the current in these four regions, from lowest to highest.

5. current density
The current density (J)
the current per unit area

6. current density
A current density J and an electric field E are established in a conductor whenever a potential difference is maintained across the conductor
Ohm’s law
 : conductivity

7. Resistance
 = 1/ : Resistivity
Resistance (.m)

8. Resistivity

9. Resistors

10. Resistance

11. Resistance and Temperature
Conductor
temperature coefficient of resistivity

12. Resistance and Temperature
Semiconductor

13. superconductor
a class of metals and compounds whose resistance decreases to zero when they are below a certain temperature Tc, known as the critical temperature

14. superconductor
A small permanent magnet levitated above a disk of the superconductor Ba2Cu3O7, which is at 77 K.

15. Electrical Power (P)
The rate at which energy is delivered to a resistor

16. Example #7
For the two lightbulbs shown in figure, rank the current values at points a through f, from greatest to least

17. Direct Current Circuits
Electromotive Force
Resistors in Series and Parallel
Kirchhoff’s Rules
RC Circuits
Electrical Meters

18. Electromotive Force
Describing not a force but rather a potential difference in volts
A battery is called either a source of electromotive force, or more commonly, a source of emf

19. Electromotive Force
The emf of a battery is the maximum possible voltage that the battery can provide between its terminals

20. Circuit Diagram
r = internal resistance
R = load resistance

21. Example #8
A battery has an emf of 12.0 V and an internal resistance of 0.05 . Its terminals are connected to a load resistance of 3.00 .

22. Resistors in Series

23. Resistors in Parallel

24. Example #9 Four resistors are connected as shown in the figure,
Find the equivalent resistance between points a and c
What is the current in each resistor if a potential difference
of 42 V is maintained between a and c

25. Example #10
Three resistors are connected in parallel as shown in the figure . A potential difference of 18.0 V is maintained between points a and b
Find the current in each resistor
Calculate the power delivered to each resistor and the total power delivered to the combination of resistors
Calculate the equivalent resistance of the circuit

26. Kirchhoff’s Rules Junction rule.
The sum of the currents entering any junction in a circuit must equal the sum of the currents leaving that junction

27. Kirchhoff’s Rules Loop rule.
The sum of the potential differences across all elements around any closed circuit loop must be zero

28. Example #11
A single-loop circuit contains two resistors and two batteries, as shown in the figure (Neglect the internal resistances of the batteries.
Find the current in the circuit.
What power is delivered to each resistor?
What power is delivered by the 12-V battery?

29. Solution #11
The 12-V battery delivers power

30. Example #12
Find the currents I1, I2, and I3 in the circuit shown in the figure.

31. Solution #12

32. RC Circuits
Charging a Capacitor

33. RC Circuits Charging a Capacitor time constant of the circuit
current at t = 0
maximum charge

34. RC Circuits
Discharging a Capacitor
Charge at t = 0

35. Electrical Meters The Galvanometer
the main component in analog meters for measuring current and voltage

36. Electrical Meters
The Ammeter
A device that measures current

37. Electrical Meters The Voltmeter
A device that measures potential difference

38. Quiz #2
Find the equivalent resistance between points a and b in the figure
If a potential difference of 34.0 V is applied between points a and b. calculate the current in each resistor.