R3 = 40 Ohms - 20 Ohms

R3 = 20 Ohms

(2) *Current in a Series Circuit.*

Since there is only one path for

current in a series circuit, the same current must flow through each

component of the circuit.

To determine the current in a series circuit,

only the current through one of the components need be known.

The fact that the same current flows through each component of a series

circuit can be verified by inserting meters into the circuit at various

points, as shown in figure 22 (on the following page). If this were done,

each meter would be found to indicate the same value of current.

FIGURE 21.

CALCULATING THE VALUE OF ONE RESISTOR IN A SERIES CIRCUIT.

(3) *Voltage in a Series Circuit.*

The voltage dropped across the

resistor in a circuit consisting of a single resistor and a voltage source

is the total voltage across the circuit and is equal to the applied voltage.

The total voltage across a series circuit that consists of more than one

resistor is also equal to the applied voltage, but consists of the sum or

the individual resistor voltage drops.

In any series circuit, the sum of

the resistor voltage drops must equal the source