Geoscience Reference
In-Depth Information
When the individual drops are known, they can be added to find the total or applied voltage by
using Equation 11.27:
E
T
=
E
1
+
E
2
+
E
3
E
T
= 25 V + 50 V + 100 V
E
T
= 175 V
Key Point 1:
The total voltage (
E
T
) across a series circuit is equal to the sum of the voltages across
each resistance of the circuit.
Key Point 2:
The voltage drops that occur in a series circuit are in direct proportions to the resis-
tance across which they appear. This is the result of having the same current flow through each
resistor. Thus, the larger the resistor, the larger will be the voltage drop across it.
11.7.6.4 Series Circuit Power
Each resistor in a series circuit consumes
power
. This power is dissipated in the form of heat.
Because this power must come from the source, the total power must be equal in amount to the
power consumed by the circuit resistances. In a series circuit, the total power is equal to the sum of
the powers dissipated by the individual resistors. Total power (
P
T
) is thus equal to
P
T
=
P
1
+
P
2
+
P
3
+ … +
P
n
(11.28)
where
P
T
= Total power (W).
P
1
= Power used in first part (W).
P
2
= Power used in second part (W).
P
3
= Power used in third part (W).
P
n
= Power used in
n
th part (W).
■
EXAMPLE 11.29
Problem:
A series circuit consists of three resistors having values of 5 ohms, 15 ohms, and 20
ohms, respectively. Find the total power dissipation when 120 volts is applied to the circuit (see
Fig u re 11.32).
R
1
5 ohms
+
R
2
15 ohms
-
R
3
20 ohms
FIGURE 11.32
Solving for total power in a series circuit.
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