3)
Let call the total resistance RT.
Craft students need only state the expression for series
connections.
Key Fact
Resistors
In series circuit, total resistance
RT ohms.2
A parallel circuit.
Now, since common all terms the equation, can divide both
sides the equation This will cancel out leave with expres-
sion for the circuit resistance:
R R
T 3
Note that the derivation this formula given for information only. The total current will divide when reaches resis-
tor junction, part flowing each resistor. For any parallel circuit, is
common all branches the circuit and
I I
T (5.
We can summarize these statements follows. The sum the individual
currents, I1, and for example Fig.2, will equal the total cur-
rent IT. 5.2, the same voltage acts across all
branches the circuit.Basic Electrical Installation Work
104
R1
R2
R3
IT
I1
I2
I3
V
FIGURE 5.4)
.
Parallel-connected resistors
In any parallel circuit, shown Fig.
From Ohm’s law know, that I
V
R
and therefore
the total current
the current through is
th
T
T
1 1
1
I
V
R
R I
V
R
e
e current through is
the current through is
2 2
2
3
R I
V
R
R I
3
3
3
V
R
(5. 5
