Basic Circuit Math

1. Circuit Math
Discovery
Lab

2. Series Circuit Math
• Current in series is constant
IS = I1 = I2 = I3 …
• Total Resistance in Series is
sum of all resistances
RS = R1 + R2 + R3 …
• Total Voltage in Series is sum
of all voltages
VS = V1 + V2 + V3 …
VS
(S stands for Series)
V1=IR1
V2=IR2
V3=IR3

3. Sample: Series. Fill in the table.
VS=40 V
321
VS
= 40 V IS
= RS =
V1
= I1
= R1 = 1 Ω
V2
= I2
= R2 = 2 Ω
V3
= I3
= R3 = 3 Ω
1. RS = R1 + R2 + R3
2. VS = I RS
4. V1 = I R1
3. IS = I1 = I2 = I3
6 Ω6.67 A
6.67 A
6.67 A
6.67 A
6.67 V
13.3 V
20.0 V

4. Parallel Circuit Math
• Voltage in parallel is constant
VP = V1 = V2 = V3 …
• Current in parallel is the sum of all
the currents
IP = I1 + I2 + I3 …
• The reciprocal of the total
resistance is equal to the sum of
the reciprocals of the individual
resistances
1 1 1 1
RP = R1 + R2 + R3 + …
VP
1
2
3

5. Sample: Parallel. Fill in the table.
Vp
= 20.0 V Ip
= Rp =
V1
= I1
= R1 = 3 Ω
V2
= I2
= R2 = 2 Ω
V3
= I3
= R3 = 1 Ω
0.545 Ω36.7 A
6.67 A
10.0 A
20.0 A
20.0 V
20.0 V
20.0 V
VP
1
2
3
1. VP = V1 = V2 = V3
2. V = I R
3. IP = I1 + I2 + I3
4. VP = IP RP
Notice that there are
more than 1 way to go
about solving these
problems! This acts as
a great way to double
check yourself!

6. Sample: Parallel. Fill in the table.
Vp
= 20.0 V Ip
= Rp =
V1
= I1
= R1 = 3 Ω
V2
= I2
= R2 = 2 Ω
V3
= I3
= R3 = 1 Ω
0.545 Ω36.7 A
6.67 A
10.0 A
20.0 A
20.0 V
20.0 V
20.0 V
VP
1
2
3
1. VP = V1 = V2 = V3
2. V = I R
3. IP = I1 + I2 + I3
4. VP = IP RP
Notice that there are
more than 1 way to go
about solving these
problems! This acts as
a great way to double
check yourself!