Series and Parallel Circuits

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Principles of Physics
 A circuit with one resistor
 When one electron leaves the
voltage supply another one enters
 How fast this exchange occurs is
based on resistance
 One electron pushes another and
so on



More than one resistor in a
single path
Each electron must go
through every resistor
Total resistance increases
with every resistor added in
series
R1


R2
Current flow depends on all
resistors
Current through each resistor
is the same
IT = I1 = I2 = …



A voltage exists across every device (voltage
supply, resistors, light bulbs, etc.)
As an electron goes through a resistor or
device it loses energy because it does work to
get through
How much energy lost per Coulomb (voltage)
depends on the resistance
R1


R2
Voltage gained by electrons
when leaving the voltage
supply equals the total
voltage lost before returning
Since voltage is lost through
all resistors
VT = V1 + V2 + …
R1
R2
To determine the current leaving
the voltage supply the total
resistance must be used
RT = R1 + R2 +…
10 Ω
12 V
14 Ω
Determine the total current in the
circuit
V = IR
12 V = I(24 Ω)
I = 0.5 A
RT = R 1 + R 2
= 10 Ω + 14 Ω
= 24 Ω
10 Ω
12 V
14 Ω
Determine the voltage in the 10 Ω
resistor
V = IR
V= 0.5 A(10 Ω)
V=5V
10 Ω
12 V
14 Ω
Determine the voltage in the 14 Ω
resistor
V = IR
V= 0.5 A(14 Ω)
V=7V
or
VT = V1 + V2
12 V = 5 V + V2
V2 = 7 V
A
5Ω
12 V
B
5Ω
5Ω
12 V
5Ω
5Ω
By adding another resistor in series
Increase total resistance
Decreases current
Voltage across each resistor decreases



Adding a resistor in series increases the total
resistance
When one resistor is disconnected the circuit is
open – current does not flow
Everyone has to go through all doors to get out

The smallest door slows the movement the most

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