1. Direct Current Circuits
Ch 18

2. Electromagnetic Force
The current in a circuit is driven by…
Generally, what is needed for motion to take place?
Consider that electric current is the movement of electrons
what is the tension (pressure) on the current?
This is also known as emf, electromagnetic force (not really a force)

3. Resistors in Series
Series circuit: only one path for the electrical current to follow

4. Resistors in Series
The current only has one path to follow The current will be the same in every device in the series circuit

5. Know your symbols

6. Know your symbols

7. Resistors in Series

8. Resistors in Series

9. Resistors in Series
The current must pass through all the objects in a series circuit
The electrons encounter the resistance of each object in the circuit
All the resistors can be summed and replaced with an equivalent
R1 + R2 + R3 + Rn … = Req

10. Voltage Drop
the supplied energy of a voltage source is reduced as electric current moves through passive elements

11. Voltage Drop

12. Voltage Drop
the supplied energy of a voltage source is reduced as electric current moves through passive elements
Calculate voltage drop using Ohm’s Law

13. Voltage Drop
What is the potential difference?

14. Voltage Drop What is the equivalent resistance?
What is the current through the circuit?

15. Voltage Drop What is the voltage drop through R1?

16. Parallel Circuits
A circuit that has more that one path that electrons can take

17. Parallel Circuits
A circuit that has more that one path that electrons can take

18. Parallel Circuits
A circuit that has more that one path that electrons can take

19. Parallel Circuits
The current does not have to go through all of the resistors
Each electron only encounters one of the branches
The amount of current can vary in the branches
Icircuit = Itotal = I1 + I2 + I3 + In …

20. Parallel Circuits
The current does not have to go through all of the resistors
Each electron only encounters one of the branches
The amount of current can vary in the branches
Icircuit = Itotal = I1 + I2 + I3 + In …

21. Parallel Circuits
The voltage drop of each branch equals the total voltage
Vtotal = V1 = V2 = V3 = Vn

22. Series and Parallel Circuits
The amount of current can vary in the branches

23. Parallel Circuits
The resistors in parallel can also be replaced with an equivalent resistance

24. Parallel Circuits What’s the voltage drop across R1? 24 V
What is the current through each branch?
1) I = V/R = 24V / 10Ω = 2.4 A
2) I = 1.2 A
3) .8 A
4) .6 A

25. Parallel Circuits What is the current through each branch?
1) I = V/R = 24V / 10Ω = 2.4 A
2) I = 1.2 A
3) .8 A
4) .6 A
What is the total current though the circuit?
5 A

26. Parallel Circuits What is the equivalent resistance?
1/Req = 1/10 + 1/20 + 1/30 + 1/40
= ohms-1
Req = 5 ohms

27. Resistivity
how strongly a given material opposes the flow of electric current.

28. Resistance in a wire
The amount of resistance in a wire is the result of four key factors
the resistivity of the material in the wire the length of the wire
the cross sectional area of the wire
the temperature of the wire

29. Resistance in a wire
The amount of resistance in a wire can be predicted
Resistance = resistivity x length / area

31. Ohmmeter/multi meeter
An instrument for measuring resistance is called an ohmmeter.
multimeter basics