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Have you ever wondered why batteries sometimes need to be inserted in alternating directions?

A typical electronic circuit has lots of components connected together with wires. How these connections are made is important and can lead to very different results depending on what’s being connected.

If you put two resistors in-line with each other, then the total resistance will be the sum of each resistor. This type of arrangement is called in series.

Electronic components don’t care about how they’re arranged in a circuit or which direction they’re facing. The only thing that matters is how they’re connected. If current has to pass through multiple resistors, then they’re in series with each other and the total resistance will be the sum of all of the resistors. In effect, they all act like a single resistor.

If current can pass through any of multiple resistors, then they’re in parallel to each other and the total resistance will be lower than the smallest resistor. How much lower depends on how many resistors and their values. What you do is add the reciprocals of each resistance and then take the reciprocal of that sum to get the total resistance. A reciprocal of a number is just 1 divided by the number. So the reciprocal of 5 is 1 divided by 5. The reciprocal of 10 is 1 divided by 10. A good calculator will even have a button just for this purpose. It’ll be labelled as 1 over X.

The important thing to remember is that placing resistors in series increase the total resistance and placing them in parallel lowers the total resistance.

What about capacitors? They can also be placed in series or in parallel. Do they behave the same way? They actually are just the opposite. If you put multiple capacitors in series, then the end result is as if you replaced them all with another capacitor where the plates are spaced further apart. This lowers the total capacitance. And putting multiple capacitors in parallel is like increasing the size of the plates. That will increase the capacitance.

So when you have capacitors in series, you calculate the total capacitance just like resistors in parallel by adding the reciprocals and then taking the reciprocal of that. And capacitors in parallel add their capacitance just like resistors in series.

Listen to the full episode to understand how batteries behave in series and parallel. You can also read the full transcript of the episode below.

## Transcript

A typical electronic circuit has lots of components connected together with wires. How these connections are made is important and can lead to very different results depending on what’s being connected.

In this episode you’ll learn about series and parallel connections with resistors, batteries, and capacitors. Make sure to listen to recent episodes to get the most out of this episode.

Let’s start with a simple circuit with just a battery and a couple resistors.

That’s not a very useful circuit. But knowing where to place resistors, of what value, and what the result will be is useful.

If you put two resistors in-line with each other, then the total resistance will be the sum of each resistor. This type of arrangement is called in series.

Imagine a narrow hallway that makes it difficult for people to walk. This is like a resistor. If you then add another hallway so that in order to reach your destination you have to walk through both hallways, then they’re in series and the total resistance is the sum of both hallways.

But what if these narrow hallways are placed so they both leave the starting room through different doors and they both arrive at the same destination. Now to get to your destination, you no longer have to walk through both hallways but can take your pick. If you have a lot of people, then some people will use the first hallway and some will use the second. The hallways can be said to be in parallel in this case. They don’t actually have to be physically laid out so they are parallel to each other.

Electronic components don’t care about how they’re arranged in a circuit or which direction they’re facing. The only thing that matters is how they’re connected. If current has to pass through multiple resistors, then they’re in series with each other and the total resistance will be the sum of all of the resistors. In effect, they all act like a single resistor.

If current can pass through any of multiple resistors, then they’re in parallel to each other and the total resistance will be lower than the smallest resistor. How much lower depends on how many resistors and their values. Let’s say that you have two 10 thousand ohm resistors in parallel. The total resistance will now be just 5 thousand ohms. The way you calculate this is a bit involved but I think I can explain here. If you don’t understand this explanation, don’t worry. It won’t stop you from understanding the rest of this episode.

What you do is add the reciprocals of each resistance and then take the reciprocal of that sum to get the total resistance. A reciprocal of a number is just 1 divided by the number. So the reciprocal of 5 is 1 divided by 5. The reciprocal of 10 is 1 divided by 10. A good calculator will even have a button just for this purpose. It’ll be labelled as 1 over X.

Back to the two 10K resistors. The capital letter K means thousand. So two 10K resistors means there’s two 10,000 ohm resistors. Since they’re in parallel, you type 10,000 in your calculator, press the 1 over X button, press the plus button, then type 10,000 and again press the 1 over X button. And then finally press equals to perform the addition and then press the 1 over X button again to get the answer which will be 5,000 ohms.

The important thing to remember is that placing resistors in series increase the total resistance and placing them in parallel lowers the total resistance.

What about capacitors? They can also be placed in series or in parallel. Do they behave the same way? They actually are just the opposite. If you put multiple capacitors in series, then the end result is as if you replaced them all with another capacitor where the plates are spaced further apart. This lowers the total capacitance. And putting multiple capacitors in parallel is like increasing the size of the plates. That will increase the capacitance.

So when you have capacitors in series, you calculate the total capacitance just like resistors in parallel by adding the reciprocals and then taking the reciprocal of that. And capacitors in parallel add their capacitance just like resistors in series.

What about batteries? And why do we sometimes need to put batteries in different directions and sometimes not? Let’s first look at what happens when you connect batteries in series and in parallel.

Remember that voltage is always a difference between two points. So a one and a half volt battery will have a potential voltage difference of 1.5 volts between it’s positive and negative terminals. Just like how you can stack blocks on top of each other to build a tower that’s even higher, you can stack batteries on top of each other to raise the voltage. You do this by connecting the positive side of one battery to the negative side of the next battery in line. You wouldn’t actually reverse a battery in this stack because then it would just try to lower the tower. As long as all the batteries are facing the same direction, then the voltages will just keep on adding. The voltage will go higher but the overall amount of time this arrangement can maintain that voltage will be the same as a single battery able to maintain its charge.

Connecting batteries in parallel is like what happens when several people try to lift or push something heavy. Each person contributes a small portion of effort. People working like this will tire less and can keep going longer. The same thing happens with batteries. Connecting them in parallel doesn’t help increase the voltage any but they can last longer.

So now if you have a flashlight and are wondering why the batteries need to be inserted in a certain order, you’ll know. Is the flashlight designed to be really bright? Then the batteries are probably going to be connected in series. Or is it more important that the flashlight last a long time? Then the batteries will be connected in parallel.

Remember it’s the connections that are important. Not the actual direction of the batteries.