1. 10.5 Resistors in Series and Parallel

2. Resistors in Series
PHET simulation

3. Resistors in Series Total resistance for a circuit in series (Rtotal)
Rtotal = R1 + R2 + R3 + …
Ohm’s Law (V = I x R)
The R typically means total Resistance (Rtotal)
Unless, you are specifically talking about the resistance, voltage, and current through one resistor

4. Resistors in Parallel
PHET simulation

5. Resistors in Parallel A little trickier
Resistance total of a circuit (Rtotal)
Rtotal = R/n (for n identical resistors)
*So, if there are 3 identical resistors, each with 60 ohms, what is the total resistance?
Rtotal = 60 ohms / 3 = 20 ohms

6. So what does this really mean?
Imagine two water slides in series
This water slide would be like one long water slide (two connected side by side)

7. So what does this really mean?
People would take longer to reach the bottom and there would also be fewer people going through the water slide each day

8. So what does this really mean?
Imagine two water slides in parallel
This would be like adding in a separate water slides, so that the people would have a choice

9. So what does this really mean?
More people would be able to go down the parallel slides each day
If the two slides were identical, they would be able to carry twice as many people as two slides in series

11. So what does this really mean?
Think of this analogy in terms of a circuit
In a series circuit, the current must go through one resistor (R1), and then another (R2)…
However, in a parallel circuit, the current is split, so that some goes through each resistor
In parallel, the amount of current leaving the battery = amount of current in each resistor

12. So what does this really mean? P. 322
Series
Parallel
Total Current
IT = I1 = I2 = I3
IT = I1 + I2 + I3
Total Voltage
VT = V1 + V2 + V3
VT = V1 = V2 + V3
Total Resistance
RT = R1 + R2 + R3
RT = R/n
For n identical resistors

13. Question
A series circuit with a 90 V source has 3 identical resistors.
An ammeter measures current leaving the voltage source as 0.1 A, what is the current through the middle resistor?
What is the resistance of each resistor?

14. Question
A series circuit with a 90 V source has 3 identical resistors.
An ammeter measures current leaving the voltage source as 0.1 A, what is the current through the middle resistor?
I (current) = I1 = I2 = I3
I = 0.1 A

15. Question
A series circuit with a 120 V source has 3 identical resistors. 2. What is the resistance of each resistor? VT = 120 V IT = 0.1 A RT = ?? R = V/I = 120 V / 0.1 A = 1200 Ohms 1200 Ohms / 3 identical resistors = 400 Ohms

16. Question
Three identical resistors are connected in parallel. In the 3rd resistor, the total resistance is 63 Ohms and the current is 23 mA.
What is the total voltage of the circuit?
What is the total resistance of the circuit?

17. VT (in parallel) = V1 = V2 = V3…
Question
Three identical resistors are connected in parallel. In the 3rd resistor, the total resistance is 63 Ohms and the current is 23 mA.
What is the total voltage of the circuit?
VT (in parallel) = V1 = V2 = V3…
V3 = I3 x R3
V3 = A x 63 Ohms = 1.45 V
V3 = VT = 1.45 V

18. Question
Three identical resistors are connected in parallel. In the 3rd resistor, the total resistance is 63 Ohms and the current is 23 mA. 2. What is the total resistance of the circuit? RT = R/n (for n identical resistors) RT = 63 Ohms / 3 RT = 21 Ohms

19. Work
Complete the handout
HW: Page 325 # 2-8