Why does current increase in a parallel circuit

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How can i calculate resistance of a wire? How do you calculate voltage drop across a resistor? How can i calculate voltage drop in a parallel circuit?

See all questions in Current and Resistance. Impact of this question views around the world. Nonetheless, when taken as a whole, the total amount of current in all the branches when added together is the same as the amount of current at locations outside the branches. The rule that current is everywhere the same still works, only with a twist.

The current outside the branches is the same as the sum of the current in the individual branches. It is still the same amount of current, only split up into more than one pathway. Throughout this unit, there has been an extensive reliance upon the analogy between charge flow and water flow. Once more, we will return to the analogy to illustrate how the sum of the current values in the branches is equal to the amount outside of the branches. The flow of charge in wires is analogous to the flow of water in pipes.

Consider the diagrams below in which the flow of water in pipes becomes divided into separate branches. At each node branching location , the water takes two or more separate pathways. The rate at which water flows into the node measured in gallons per minute will be equal to the sum of the flow rates in the individual branches beyond the node.

Similarly, when two or more branches feed into a node, the rate at which water flows out of the node will be equal to the sum of the flow rates in the individual branches that feed into the node. The same principle of flow division applies to electric circuits.

The rate at which charge flows into a node is equal to the sum of the flow rates in the individual branches beyond the node. This is illustrated in the examples shown below. In the examples a new circuit symbol is introduced - the letter A enclosed within a circle. This is the symbol for an ammeter - a device used to measure the current at a specific point. An ammeter is capable of measuring the current while offering negligible resistance to the flow of charge.

Diagram A displays two resistors in parallel with nodes at point A and point B. Charge flows into point A at a rate of 6 amps and divides into two pathways - one through resistor 1 and the other through resistor 2. The current in the branch with resistor 1 is 2 amps and the current in the branch with resistor 2 is 4 amps. After these two branches meet again at point B to form a single line, the current again becomes 6 amps. Thus we see the principle that the current outside the branches is equal to the sum of the current in the individual branches holds true.

Diagram B above may be slightly more complicated with its three resistors placed in parallel. Four nodes are identified on the diagram and labeled A, B, C and D. Charge flows into point A at a rate of 12 amps and divides into two pathways - one passing through resistor 1 and the other heading towards point B and resistors 2 and 3. The 12 amps of current is divided into a 2 amp pathway through resistor 1 and a 10 amp pathway heading toward point B.

At point B, there is further division of the flow into two pathways - one through resistor 2 and the other through resistor 3. The current of 10 amps approaching point B is divided into a 6-amp pathway through resistor 2 and a 4-amp pathway through resistor 3. Thus, it is seen that the current values in the three branches are 2 amps, 6 amps and 4 amps and that the sum of the current values in the individual branches is equal to the current outside the branches.

A flow analysis at points C and D can also be conducted and it is observed that the sum of the flow rates heading into these points is equal to the flow rate that is found immediately beyond these points.

The actual amount of current always varies inversely with the amount of overall resistance. There is a clear relationship between the resistance of the individual resistors and the overall resistance of the collection of resistors. Since the circuit offers two equal pathways for charge flow, only one-half the charge will choose to pass through a given branch. With three equal pathways for charge to flow through the external circuit, only one-third the charge will choose to pass through a given branch.

This is the concept of equivalent resistance. The equivalent resistance of a circuit is the amount of resistance that a single resistor would need in order to equal the overall effect of the collection of resistors that are present in the circuit. For parallel circuits, the mathematical formula for computing the equivalent resistance R eq is. The examples above could be considered simple cases in which all the pathways offer the same amount of resistance to an individual charge that passes through it.

The simple cases above were done without the use of the equation. Yet the equation fits both the simple cases where branch resistors have the same resistance values and the more difficult cases where branch resistors have different resistance values. For instance, consider the application of the equation to the one simple and one difficult case below. It has been emphasized throughout the Circuits unit of The Physics Classroom tutorial that whatever voltage boost is acquired by a charge in the battery is lost by the charge as it passes through the resistors of the external circuit.

The total voltage drop in the external circuit is equal to the gain in voltage as a charge passes through the internal circuit. In a parallel circuit, a charge does not pass through every resistor; rather, it passes through a single resistor. Thus, the entire voltage drop across that resistor must match the battery voltage. As with alternating current, however, simple Children should identify complete loops in battery-powered devices and devise their own records of that loop, using their own Classroom Activity Electrical Circuit.

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