Figure 5.

Parallel-resistive circuit.

value plus that of the added path. In figure 5, if only R1 is connected to the 6-

volt source, it is known by Ohm's law (I = E/R) that the current is 6/3, or 2

amperes. When R2 is added, the same voltage is applied to it as was applied to R1.

The current through R2 must equal 6/2, or 3 amperes.

The total current from the

source is now 2 plus 3, or 5 amperes. When R3 is added, the total current from the

battery will be increased another 3 amperes or will equal 2 plus 3 plus 3, or 8

amperes. The greater the number of branches in a parallel circuit, the greater is

the current flow from the source.

c. Resistance.

Since the total current in the circuit and the applied

voltage are both known, the combined resistance of R1, R2, and R3 may be

calculated: R = E/I = 6/8, or 0.75 ohm. Note that the combined resistance is less

than the smallest value of any one resistor in the parallel combination.

d. Laws.

The three important laws relating to parallel circuits are:

(1) In a parallel circuit the same voltage is applied across each element.

(2) The total current in a parallel circuit is equal to the sum of the

currents flowing in the individual branches.

(3) The combined, or total, resistance of a parallel circuit is equal to

the applied voltage divided by the total current.

e. Combining Parallel Resistances.

(1) One method of determining the total resistance of a parallel circuit

was shown in c above. This method is satisfactory, provided the

Integrated Publishing, Inc. |