Resistor before or after LED?

I just published a new video where I answer the question:

“Does the resistor go before or after the LED?”

You can find the video here:

https://youtu.be/zWC_AiycHbo
If you don’t want to watch the video, I’ve attached the script below so you can read it instead:

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[VIDEO SCRIPT]:

This is an LED.

If the LED gets too much current flowing through it, it will burn out and die.

So it always needs a resistor to protect it.

But, in which order?

Here’s the thing…

It doesn’t matter!

The resistor can go before – or after – the LED, and it will still protect it.

You see…

the current that flows out of a battery is always equal to the current that flows back into the battery.

So in a circuit like this – with only one path for the current to flow – the current is the same everywhere in the circuit.

The current through the resistor is the same as the current through the LED.

Now, you might wonder – what controls the current then?

An LED has something called a “forward voltage”.

That’s the voltage drop the LED will have under normal conditions.

A typical forward voltage is 2V.

In a circuit with a 9V battery, an LED, and a resistor, you will have 2V across your LED.

The rest of the voltage – 7V – will be across the resistor.

Ohm’s law tells you that current equals voltage divided by resistance.

So if you have a 1000 Ohms resistor, you would get 7 divided by 1000 equals 0.007 – which is 7 mA.

Since the current is the same everywhere in the circuit, you’ll also get 7 mA through the LED – no matter if the resistor is before or after the LED.

What matters is the size of the resistor.
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Keep On Soldering!
Oyvind @ build-electronic-circuits.com

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