The answer to whether current is constant in a parallel circuit is definitively no. A parallel circuit is an arrangement where the electric current encounters a junction and splits to travel along two or more separate paths before recombining. Because the total flow of charge must divide among these multiple branches, the current cannot remain the same throughout the entire circuit. The overall current supplied by the source is the sum of the individual currents flowing through each separate pathway.
Voltage as the Constant Factor
The defining feature of a parallel circuit is the electrical potential difference, known as voltage, which remains uniform across all components. Every branch is connected directly across the terminals of the power source, such as a battery or wall outlet. This direct connection ensures that the full potential difference provided by the source is applied to every component simultaneously. Unlike a series circuit, where the voltage is divided, the parallel configuration ensures each load receives the same electrical push. The uniformity of voltage is the foundational principle that dictates how current must behave in the circuit.
Current Division and Kirchhoff’s Law
The phenomenon of current splitting at a junction is governed by Kirchhoff’s Current Law (KCL). This law states that the sum of the currents flowing into any junction, or node, must equal the sum of the currents flowing out. This principle is a direct consequence of the conservation of electric charge. For example, if 5 amperes of current enter a junction, the sum of the currents in all the branching paths must also total exactly 5 amperes. When the individual branch currents recombine, the total current returns to its original value before flowing back to the power source.
How Resistance Determines the Split
While Kirchhoff’s Law explains that the current divides, Ohm’s Law explains how the current divides among the parallel branches. Ohm’s Law establishes the relationship between current (I), voltage (V), and resistance (R), expressed as I = V/R. Since the voltage is the same across every parallel branch, the current flowing through any specific branch is inversely related to its resistance. A path with lower resistance offers less opposition to the flow of electrons, allowing a proportionally larger amount of current to pass through it. If one branch has a resistance of 10 ohms and another has 20 ohms, the 10-ohm branch will carry exactly twice the amount of current as the 20-ohm branch.
Practical Uses of Parallel Circuits
The current-dividing nature of parallel circuits is indispensable for almost every real-world electrical system, most notably in household and building wiring. Connecting devices in parallel allows each appliance or light fixture to operate independently of the others. If one device, such as a lamp, is turned off or burns out, it only stops the current flow in its specific branch, leaving all other parallel branches completely unaffected. This arrangement ensures that every appliance receives the full, consistent line voltage, typically 120 volts in North America. Furthermore, this independent operation increases reliability and safety, as circuit breakers monitor the total current drawn by the combined branches and interrupt the flow only if the sum exceeds a safe limit.