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Parallel circuits are very useful - we often use them when we want components to work independently.
But how does the current and potential difference vary in a parallel circuit? Let's learn all about it!
What is a parallel circuit?
A parallel circuit is a circuit where the components can be found in two or more different loops. In a parallel circuit, the electricity has different pathways it can flow through.
What happens to the current in a parallel circuit?
Let's take our example from the start of this activity. We will visualise the current using arrows.
We can imagine that the electricity flows from the positive terminal of the cell. The current is the rate of flow of charged particles.
At point X on the diagram, the current reaches what we call a junction. Here, the flow of electricity splits, and some current continues to flow from left to right, and some of the current flows down.
When current reaches a junction, it splits, some going one way and the rest going another.
From the diagram, you might be able to see that, just before the electrical flow returns to the cell, the current has joined back up.
So, what does this look like in practice, when we use ammeters to measure the current?
We can see that 3 A of current flows from the cell. The current splits at each of the junctions, and 1 A of current flows through each of the three loops. The current is evenly divided between the three loops with three identical bulbs.
The current is measured at 3 A again before the flow of electricity returns to the cell.
What happens to the potential difference in a parallel circuit?
To understand this next concept, we need to remember that the potential difference is a measure of the amount of electrical energy transferred. All of the charge carriers (the electrons in the wires) deliver the same electrical energy.
Here is another parallel circuit, this time with voltmeters to measure the potential difference.
The cell produces a potential difference of 5 V. The energy is carried around the circuit. The current splits at the junction, but, the potential difference hasn't changed. So, the potential difference of each loop will be equal to the potential difference provided by the cell!
More complex circuits
Some circuits include both series and parallel elements. Here is an example, of a cell and three identical resistors.
In this circuit, there are two parallel loops. The first parallel loop has resistor X and resistor Y in it. The second loop has resistor Z.
Resistor X and resistor Y are in series with each other because they are both in the same loop. That means that, no matter where we measure the current in this loop, it will always be the same.
The current in a parallel circuit is shared. We can think of it like this:
Current in loop 1 + current in loop 2 = current at the cell.
If the cell produces a potential difference of 4 V, resistor Z will have a potential difference across it of 4 V. But, resistor X and resistor Y will each have a measured potential difference of 2 V, as the 4 V is shared between them in the loop.
Now, let's try some practice questions!
