Circuit consisting of two or more components is common thing. These components in circuit can be connected in two different ways i.e. series or parallel. Now, the questions are, what is series connection? What is parallel connection? What are the advantage of series connection or parallel connection? How is voltage and current in case of series or parallel connection? What are the reallife application of series and parallel connection? Well, I am going to answer all these questions in this article so, if you want to have the answers and the basics of series and parallel connection, read this article.
Before getting to content directly, I would like to tell you guys that, people who are having their interest in electrical wiring or PLC programming, or some logical wiring, must go through this article because, this will make your basics very clear.
So, first take a look at the things that you will be understanding today –
 What is series connection?
 Key points and application of series connection.
 What is parallel connection?
 Key points and application of parallel connection.
To understand these connections, consider an example of water pump and pipes. Let’s say you are having three pipes and a water pump. You connected those three pipes as shown in figure 1. Now how will water flow? Yes, you guessed it right, from pipe A – B – C and then in to the tank. As you can see, there is only one flow of water through out all the pipes and there is equal amount of water in all the 3 pipes. This is nothing but an example of a series connection!
Fig 1
Now, let’s say I connected the pipes in the way as shown in figure 2. In this case water, will flow through pipe A then some part of water will get divided into pipe B and remaining will continue to flow in pipe A, again it will get divided in pipe C and remaining will continue in pipe A (Fig 2). As you can see there are multiple flow of water in this type of connection and the quantity of water may be different in all the 3 pipes (depending upon the size of pipe). This is an example of parallel connection!
Fig2
If you understand this pump and pipe example, you have understood 50% of stuff. Yes, it is as simple as that. Remaining 50% you’ll understand soon, just keep reading.
 Series connection.
First let’s get into the details of series connection. Instead of a pump let’s say, we have a battery, instead of pipes we have resistors and instead of water, current is flowing. You’ll get the details in the below figure 3.
If resistors are connected end to end than it is called as a series connection.
Alike water, current has a single flow and it is equal in all the 3 resistors. But, what about voltage? Will it be also equal? No, it will not. The total voltage will get distributed across each resistor (the amount of voltage across a resistor depends upon the value of its resistance), and this is called as “voltage drop”.
So, how to calculate total voltage drop in the circuit? It’s simple, while calculating remember we have voltage of 9 volts and it’s ‘total voltage’, and to calculate ‘total current’ in the circuit we’ll need ‘total resistance’ (ohms law V=IR) but, what we have is individual resistance and that will not work. So, what we need to do is simply find out total resistance by adding all the 3 resistances. Remember resistance in series adds! (If you want to have details about resistance and how they behave, click here – Resistance and Ohm’s Law.)
R total = R1 + R2 + R3
R total = 3 + 5 + 10
R total = 18 ohms
Now, as you have total resistance you can calculate total current flowing thorough the circuit by ohms’ law.
I = V/R
I = 9/18
I = 0.5 mA
This 0.5 mA is the current flowing through each of the resistor. As you now have the current through each resistor you can now calculate voltage drop across each resistor by using ohms’ law.
Voltage drop across 3ohm resistor is = I x R = 0.5 x 3 = 1.5V
Voltage drop across 5ohm resistor is = I x R = 0.5 x 5 = 2.5V
Voltage drop across 10ohm resistor is = I x R = 0.5 x 10 = 5V
Now, here comes the magical thing, let’s add the voltage drop across each resistor
= 1.5 + 2.5 + 5 = 9V
Addition of voltage drop across each resistor is 9 volts, which is nothing but our source voltage!
Now we’ll see what are the key points in series connection –
 Current through any component is equal, because electron has only one path to flow.
 Voltage across each component is different.
 Total voltage in series circuit is equal to the drop across each individual. (Vtotal = V1 + V2 + V3).
 Resistance adds up in case series connection.

Application of series connection –
 Series connection is generally used where voltage division is needed.
 Reactors in power systems are connected in series.
 Most of the logical wiring where multiple conditions are to be checked is connected in series.
These are the few application of series connections.

Parallel connection.
Now, instead of connecting 3 resistors in series we’ll connect them in the other way like we connected pipes (fig 2). Alike water, current gets divided in this type of connection (fig 4), as there are multiple paths to flow. So, the current through each resistor will be different. The connections where current has number of paths to flow is called as parallel connection.
So, current will going to be different across each resistor but what about voltage? Voltage in this case remains equal across each resistor as the resistor are directly connected across the battery. Now, as you know resistance of each resistor and voltage across it, you can calculate current flowing through each resistor.
I1 = V/R1 = 9/10 = 0.9 mA.
I2 = V/R2 = 9/2 = 4.5 mA
I3 = V/R3 = 9/1 = 9 mA
These currents are individual current flowing through their respective resistor, we still don’t know the total current and total resistance. In this case, total current is equal to the sum of all individual current.
I total = I1+I2+I3 = 0.9 + 4.5 + 9 = 14.4 mA
So, now you have total voltage and total current from this you can calculate total resistance of circuit by using ohm’s law.
R = V/I = 9/14.4 = 0.625 k ohms.
Here you may have observed the total resistance of the circuit is very low as compare to the individual resistance. That’s the property of parallel circuit, ‘total resistance reduces in case of parallel connection’. If you want to have details about how resistance behave click here, Resistance and Ohm’s Law.
Let’s list out what are the key points in parallel connection
 Voltage remain same across each resistor.
 Current has multiple path to flow and hence, current flowing through each resistance is different.
 Total resistance decrease in case of parallel connection.
 Total current is equal to the sum of individual current.

Application of parallel connection
The biggest application of parallel connection is the wiring in our home. The wiring of our home is in parallel because, equipment we use every day are design for standard voltage of 230V AC (in case of India it may be different for different country) and current of each equipment is different and this can be satisfied by parallel connection only.
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