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
(5.2
A parallel circuit.
Key Fact
Resistors
In series circuit, total resistance
RT ohms.
Parallel-connected resistors
In any parallel circuit, shown Fig.2, will equal the total cur-
rent IT. For any parallel circuit, is
common all branches the circuit and
I I
T (5. The sum the individual
currents, I1, and for example Fig. 5.3)
Let call the total resistance RT.
We can summarize these statements follows.Basic Electrical Installation Work
104
R1
R2
R3
IT
I1
I2
I3
V
FIGURE 5. The total current will divide when reaches resis-
tor junction, part flowing each resistor.
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.4)
.
Craft students need only state the expression for series
connections. 5.2, the same voltage acts across all
branches the circuit
