Equivalent Resistance
Resistors in Series
As you add resistors
1.5 V
in series, you increase
resistance. Simply add
1.5 V
the amounts together.
Rtotal = R1 + R2 + R3 ...
Resistors in Parallel
12
10 Ω
12 Ω
15 Ω
1.5 V
As you add resistors in parallel, you open more paths for the electricity to
flow, increasing total current, and decreasing total resistance. For resistors in
parallel, the total resistance is always less than the smallest resistor.
A 4
1. These resistors are in:
RT = R1 + R2 + R3…
RT = 10 + 12 + 15
RT = 37
15
1.5 V
1
1 1 1
= + + ...
Rtotal R1 R2 R3
Example: Calculate the
total resistance of this
circuit.
10
Example: Calculate the total
resistance of this circuit.
1
1
1
= +
+ ...
R T R1 R 2
1
1 1 1
= + + = .1+ .083 + .067
RT 10 12 15
1
1
RT =
= 4Ω
= .25
.25
RT
11. A2 reads (current 2 = )
B
12
2. What is Rtotal from A to C?
3. What is Rtotal from B to D?
C
4. What is Rtotal from A to D?
8
D
5. Calculate the total resistance.
12. A3 =
12V
6Ω
6Ω
6Ω
13. A4 =
2Α
14. Since V = IR and
R = V/I, Rtotal =
A3
A2
A4
15. If one of the resistors is removed, Rtotal =
4
6. Calculate total voltage.
6V
18
7. Calculate total current.
6V
16.You are given four 100
A. If in series Rtotal =
resistors.
6
B. If in parallel Rtotal =
8. Calculate the total resistance.
17. Without calculating, you know
that Rtotal must be less than:
8
20
10
8
6
18. Calculate Rtotal.
9. How does Rtotal compare with
the individual resistors?
20
10.Why?
19.Calculate and label the total
resistance for each pair of
resistors in series.
20.Calculate the total resistance for
the two parallel branches.
cstephenmurray.com
3Ω
10 Ω
5Ω
2Ω
21. What is the equivalent
resistance of the parallel
resistors?
22. Calculate Rtotal for all three
resistors.
200Ω
200Ω
200Ω
Copyright © 2013, C. Stephen Murray