# When putting a Resistor in series with an LED

• AchillesWrathfulLove
In summary: Resting potential (difference) of a typical neuron is about 70 mV, across a membrane approx. 10 nm thick. This gives 7 MV/m.

#### AchillesWrathfulLove

When putting an LED in series with a Resistor do you put it according to current convention (positive to negative) or to the actual current flow? Does it matter?

#### Attachments

• R-LED Circuit.png
5.7 KB · Views: 357
What is the role of the resistor, and will its position in the circuit change the way it works?

berkeman
AchillesWrathfulLove said:
When putting an LED in series with a Resistor do you put it according to current convention (positive to negative) or to the actual current flow? Does it matter?
The two diagrams you have shown are absolutely identical in every significant respect, and that would be true regardless of what element was in the place where you show the diode. If you don't understand that, then you seriously need to get back to basics before trying to go further.

phinds said:
The two diagrams you have shown are absolutely identical in every significant respect, and that would be true regardless of what element was in the place where you show the diode. If you don't understand that, then you seriously need to get back to basics before trying to go further.

I have only studied Circuit Analysis with Resistor networks and now beginning to get into RC/RL Circuits so I don't really have an idea how circuits function in reality with my current knowledge, heck I don't even know fully what an LED is. This is something I google about out of my own spare time to understand more about circuits.

Anyways... But wouldn't you want the resistor being the first thing to take in the current BEFORE it hits the diode instead of AFTER it hits the diode?

AchillesWrathfulLove said:
I have only studied Circuit Analysis with Resistor networks and now beginning to get into RC/RL Circuits so I don't really have an idea how circuits function in reality with my current knowledge, heck I don't even know fully what an LED is. This is something I google about out of my own spare time to understand more about circuits.
Then I say again, you need to go back to basics. You are getting ahead of yourself and trying to learn in a very scatter-shot way. Not a good idea.

Anyways... But wouldn't you want the resistor being the first thing to take in the current BEFORE it hits the diode instead of AFTER it hits the diode?
When you get back to basics you will realize that it it utterly irrelevant and in fact your question doesn't even make any sense.. The current in a series circuit goes through everything at the same time.

Fisherman199 and Guineafowl
You are trying to tackle speed-density engine maps without understanding that there are pistons going up and down inside...

Seriously, get a decent book (as recommended in your other thread) and start at the beginning. Voltage, current, charge, resistance... These concepts are deceptively simple and it’s tempting to skip over them quickly; however, they are the foundation of all your future studies. Learn them well; read different accounts from different authors; set out a piece of paper and pretend you’re explaining the concepts to someone else.

Otherwise you’ll end up like the narrator of a ‘science’ documentary I saw recently, who spoke of “4000 volts of direct current”.

davenn and phinds
Guineafowl said:
Otherwise you’ll end up like the narrator of a ‘science’ documentary I saw recently, who spoke of “4000 volts of direct current”.

I just read a pop-sci book on biochemistry, where the author (PhD, professor in evolutionary biochemistry, so not some random person) claimed there is an electric field in the cell membranes reaching 30 MV/m* "as in a lightning".

*Haven't checked, but the number itself looks reasonable, something like a bit over 100 mV across membrane several molecules thick can yield this order of magnitude.

Borek said:
I just read a pop-sci book on biochemistry, where the author (PhD, professor in evolutionary biochemistry, so not some random person) claimed there is an electric field in the cell membranes reaching 30 MV/m* "as in a lightning".

*Haven't checked, but the number itself looks reasonable, something like a bit over 100 mV across membrane several molecules thick can yield this order of magnitude.

Resting potential (difference) of a typical neuron is about 70 mV, across a membrane approx. 10 nm thick. This gives 7 MV/m. That’s given me a new appreciation of the dielectric properties of the phospholipid bilayer!

## 1. What is the purpose of putting a resistor in series with an LED?

The resistor helps to limit the amount of current flowing through the LED. LEDs are sensitive electronic components and can easily be damaged by too much current. The resistor ensures that the LED receives the correct amount of current to function properly.

## 2. How do I calculate the value of the resistor needed for my LED?

The value of the resistor can be calculated using Ohm's Law (R = V/I), where R is the resistance in ohms, V is the voltage across the resistor, and I is the current flowing through the resistor. The voltage across the resistor can be calculated by subtracting the forward voltage of the LED from the supply voltage. The desired current can be determined by looking at the specifications of the LED.

## 3. Can I use any type of resistor with an LED?

It is best to use a current-limiting resistor specifically designed for use with LEDs. These resistors are able to handle the high power dissipation that occurs with LEDs and are designed to provide a stable current flow. Using the wrong type of resistor can result in damage to the LED or an unstable circuit.

## 4. Can I put multiple LEDs in series with one resistor?

Yes, it is possible to put multiple LEDs in series with one resistor as long as the total voltage drop across the LEDs does not exceed the supply voltage. The resistor value will need to be calculated based on the total voltage drop and desired current for all the LEDs in the circuit.

## 5. What happens if I don't use a resistor with my LED?

If a resistor is not used in series with an LED, it will likely be damaged due to too much current flowing through it. This can cause the LED to fail or become dimmer over time. In some cases, the LED may also get very hot and potentially melt or catch fire. It is important to always use a resistor with an LED to ensure its proper function and longevity.