In this video I’m going to talk about electrical

resistance, ohm’s law, and how to pick a resistor to limit

current in an LED circuit. In previous videos I talked about how voltage

can behave like a pushing force, pushing electric current

around a circuit. But in one example I connected an LED straight

to 7.5V, way too much current flowed, and the LED blew up. So you can see how it would be useful if there

was something that could resist the flow of electrical current. Something that could tame the flow in a controlled

way. That device is called a resistor, and here

are some examples of what resistors can look like. We’ve got a

very basic resistor over here, which is the kind of resistor that most hobbyists would

use at home when constructing circuits. And over here we have a tiny surface mount

resistor. This is something you’d expect

to see in a small device like your phone. And this big resistor is the type of thing

you’d use large power supply. So how do these resistors work? Remember how in my video about current, I

talked about electrons jumping from atom to atom, all at the

same time, like a conga line? Well in reality this process is not 100% efficient. The atoms in a material like

copper wire are always vibrating around just a little bit, and this is because of the heat

energy they have. When electrons try to move through the wire,

sometimes they’ll bump into an atom that’s in the way, and

effectively the flow of current gets resisted. As this happens, some of the kinetic or movement

energy from the electrons gets converted into heat. This is the fundamental principle behind how

electric heaters and incandescent light bulbs work. But it’s not just metals that have the property

of resistance, resistance can exist simply from the fact that some materials

just don’t have a suitable arrangement of atoms for

electrons to flow through. And some materials just don’t have enough

free electrons floating around for large amounts of current to flow. Keep in mind this is a huge simplification

and this is not how actual atoms and electrons are going to look and

behave at the subatomic level. Nearly everything on earth has some resistance

to electrical current, and metals tend to have the least

resistance. Sorry, I

had to put it in the video somewhere. We measure the amount of resistance with a

unit called ohms. The symbol is the greek letter omega. To give you a sense of scale, a resistance

of under 1 ohm is considered to be a very low resistance. That’s

something that you’d expect to see from a piece of wire that’s good at conducting electricity. 1 million

ohms, or 1 megaohm, is generally considered to be a very high resistance. That’s something that you might

expect to see from a bad conductor of electricity like this dried out piece of carrot. This thing that I am using to measure resistance

is called a multimeter, and it can measure the resistance of

almost anything. I have a separate tutorial on multimeters,

and I recommend you watch it as soon as possible to learn more about this important

tool. Now if you’re playing with electronics at

home, you’ll be using resistors that look like these. They have

colored bands on them, and there’s a special code that lets you translate the colors into

a resistance value. For example these red, violet, brown and gold

bands mean this is a 270 ohm resistor. Now you can

memorize the color code, but it’s a lot easier to just use one of the many resistor calculators

out there. Just search for resistor color calculator

on Google or in your phone’s app store. By having resistors with specific resistance

values we can carefully control the amount of current that

flows in a circuit. Today, let’s start out with everyone’s first

simple resistor circuit, using a resistor to limit

the current going through an LED. Make sure you’ve already watched my LED tutorial

and have bought some LEDs and resistors, which I am going

to link again in the video description section. In order to do the math for this circuit you

need to know about the mathematical relationship between

voltage, current and resistance. Here’s an old comic that I’ve always liked

that illustrates the relationship on an intuitive level. More formally, we use this equation. Ohm’s law. In textbooks you usually see it written as

V=I times R. Or voltage=current times resistance. If you use a little algebra you can rearrange

the equation to calculate any of the variables as long as you know the

other two. Although it’s important to understand that

all these versions of the equation are exactly the same thing,

our LED circuit is going to be using this version, so let’s focus on that. Let’s say we have a 10 volt power source,

and we want to make sure that no more than 10mA flows from

it. We can use ohm’s law to figure out what resistor

will accomplish this. The answer is really simple, just take the

voltage, divide it by the desired current, and we get the answer of

1000 ohms. So now we can either use the resistor color

code, or a resistor calculator app to figure out

what a 1000 ohm resistor looks like, and it turns out to be brown, black, red. The 4th color band all the way

on the right refers to the tolerance of the resistor. A real world 1000 ohm resistor might actually

have a resistance of 1020 ohms, or 998 ohms, and

for most circuits you play with at home +/- 5% will be good

enough. So let’s double check our math in real life. I’ve got my power supply set to 10 volts,

it’s hooked up to a 1k resistor, and as you’d expect, 10mA is flowing

from the power supply. It’s also important to know that ohm’s law

is a linear relationship, meaning that for a fixed resistor value, if

you double the voltage, you double the current. Here’s 20 volts going into the same 1000 ohm

resistor, and as you’d expect, the current doubles to 20mA. I want you to understand that only pure simple

resistors obey Ohm’s law. The relationship between voltage and current

for most electronics is a lot more complicated than this. In a lot of cases things will work fine up

until their recommended voltage level, and if you exceed that then

things suddenly blow up. But for now, resistors are good enough to

help us limit current in a simple LED circuit. Let’s start out with a 9 volt battery, a resistor,

and an LED connected with the correct polarity. And notice

that it doesn’t matter which way we connect the resistor – unlike the LED, polarity doesn’t

matter for resistors. We want to find out what resistor will let

us safely use 9 volts with this LED. In my previous video

about LEDs we talked about forward voltages, and for this particular white LED the forward

voltage is 3 volts. That means that when the LED is on, there

is going to be a 3 volt drop across it. So… what is the

voltage across the resistor? Remember that voltage is all about differences

in electrical potential between two points. Our power source is a 9 volt battery, so we’ve

got 9 volts between here and here, and we’ve got 3 volts across the LED. So this must mean that we’ve got 6 volts across

this resistor, because 9 – 3 is 6. Ok so we’ve got our voltage. Now the current in this circuit is going to

be whatever we want to it to be. But the recommended maximum current for this

LED is 20mA, so we’re going to use that. And notice that I

am using conventional current here which moves from positive to negative. That’s what you are going to

see in every single electrical engineering situation, theoretical physics classes might

use negative to positive electron flow. So let’s apply Ohm’s law now. 6 volts divided by 20mA gives us a resistance

value of 300 ohms. Now I don’t have a 300 ohm resistor in my

parts collection, but a 330 ohm resistor will be good enough. If

you are messing around with LEDs at home it doesn’t matter if you get the current wrong

by 10%. Ok, so here I have my 9 volt battery and a

9 volt battery clip. The red positive wire is going to one side

of my 330 ohm resistor, and that’s going to the

LED’s anode. Then I’m just connecting the negative wire

from my battery to the LED’s cathode. 9 volts, roughly 20mA, and no exploding LEDs! Finally! If we increase the resistance to, let’s say,

18 kiloohms, we’ll get less current, and as you’d expect, the LED

is dimmer. In general, this is the equation you can use

to calculate the resistor for a simple LED circuit. But… there is a limitation! I’ve got another power supply here set to

give me 140 volts, and that’s enough to mess you up so don’t do

this at home. Let’s put 140 volts into this equation, we’ve

got 3 volts for our white LED, and we want to

stick to the 20mA current limit. So we get a resistance value of 6,850 ohms. I’ve got a 6.8k resistor in my

parts collection, which is very close to our theoretical value, so let’s see what happens. Huh. Now instead of the LED getting toasty, the

resistor gets too hot. So what’s going on here? To answer

that you need to learn about electrical power, which will be the subject of my next video. Finally, I can’t make a video about ohms without

mentioning Ohmnilabs! It’s a company run by a few

friends of mine that make some pretty cool robots. Check them out at ohmnilabs.com. Thank you for watching, subscribe and check

out the video description section to learn more about

electronics!

Do electrons actually move at approximately the speed of light? Not quite. It is an electric

fieldthat "moves". In a one meter wire, with one amp current, electron particles take 24 hours to move the length of the wire.I lost you in this video…:/

So letโs say I have a 8ohm amp that is 10 watts per channel, can I run it to a 4ohm speaker that is 30 watts rms. Without breaking the amp or blowing the speaker

I humbly disagree, it is easier to memorize the colour bands. I did it as a schoolboy in the eighties and it is still with me, forty years later.

So you say keeping the current off by 10% is not a problem? im asking because i have 2x AA batterie in series with 1.6V and my LED is recommended for 3V and 20mA. so i don't need to get a resistor at all? Im just double checking. 3.2V-3V = 0.2V –> 0.2V/0.02A = 10 Ohm. with 10% Current diviation i would be at 3.2V-3.3V and therefore 0V/0.02A=0 ๐

Sweet ohm Alabama.

Thank U , Valueable

I don't understand, I generated 10V using self made battery using coper and zync and use water as solution, I attached the 3V led and it barely glows, the 10V drops down to 2.4V. how do I get more Amps or what do I need to do to keep the Voltage to 10 or at least not to drop so low?

why don't you have a video on how to find the resistance value of a resistor with their bands

so with atoms moving due to heat and power drops due to heat transfer. is that why they super cool things now i.e super conduction

Resistance is not futile

Great video, all are great in fact. I'm just starting out with electronics and your videos explain things by well. Thanks. Subscribed.

Complete newb here actually taking notes like this is a school lecture. ๐คฃ So helpful!

Thanks

But please upload video on

How many give resistance in the way of crunnt

Your videos are Awesome! It took me 2 years to fully understand all of these things myself, if I would have found this channel beforehand it would have taken 2 days. I hope your videos get to as many enthusiasts as possible!

Thank You!

Sir if we want to connect 3LEDs in

Series

With 9V battery which value resister is recommended.

Also if we connect them in parallel then which Resistor is recommended.

Plz reply or make a detailed video in this scenario

Thanks

Thank you.

โค๏ธโค๏ธโค๏ธ๐จ๐ฆ

Where did you get the comic picture? Can I use it in my video?

3:50 has done a much better explanation than anything anyone else has ever told me.

French version of Ohm's law : U = R x I.

Hi! Is the resistance calculated differently for a string of 20 LEDs?

I feel bad for that rasberry pi

Everyone knows about resistance.

Itโs futile.

Nice video, and a very easy to swallow robot ad.

Hi, Thanks for the video, very informative. Do you know if there is a LED that works with 7uA at 1.1V? Thanks,

I need to buy pass the light affect on my rotary or rewire it to turn off by a switch

As per electron flow we need to connect resistor from Negative side of battery and LED, but we are connecting on positive side.

So this electron theory is right or wrong? as per concept due to electron flow we got electricity. What is correct? Or any other charge is there.

OK I've looked at the comments and didn't find what I was looking for . So I guess I'm the one who will say …….

" Resistance is futile " . After reading the comments I wouldn't worry about being assimilated .

It would cause a Downgrade in the Collective .

voltage drop minimize current manage current = carbon resistor 2 wire wend resistor .3 un flamable resistor v variable resistor resistor not short they break . checking resistor color and code need any one in computer hardware

thank you for the explanation, this is very easy to understand

Join the resistance! Viva La Ohm!

I have just found this video. Thanks. I will watch it again when I get ohm.

This video explained well than my electrical subject professor whom I paid a lot. life sucks

Why all the resistance???

2:11 true

Resistance is futile

Someone in here asked a good question: Does it matter where in this circuit one places the resistor? (1) Why or why not? (2) Where should the resistor go? (3) In DC, where do the electrons really come from–positive side or negative side?

That poor Pi…

Irresistible!!

…WILL THIS WORK WITH A EVERY READY 9 VOLT BATTERY?

An easy way to remmeber the equation is a triangle E at the top I bottom right R bottom left. Then you can work out which values in what place. I have discalculear ( like dslexia only with numbers) so anything to make maths easiear. You also forgot the 4th band on the resistor. Gold +/- 5% Silver +/- 10% no band +/- 20%

Why do you and everyone else say that resistors resist current (amps) when they also affect voltage?

This is why it is so confusing.

00'.20" That poor wee LED … ๐ข Good video, thank you. R

Wow…this video is very creative with live electrical components!!!๐

nice i wish i had a proper DC power supply haha. just using a battery.

RIP raspberry pi

btw its runs on 3.3v logic

7:23

i don't get this.

if all the resistance in this case is is taking the voltage and dividing by the current, you could still get exactly the same resistance with vastly different values for voltage and current. 3v and 10mA would also give 300ohms. how does the resistor know exactly the right balance of volts and amps you want it to pass?

Omg… this was a huge help!! Thank you so much!! Iโll sub to that!!

… Rรฉsistors – are like Rings of Saturn – one against all in your Radio.

Great job sir! Awesome work.. I think you should do all the videos on Youtube period. Well done! I was just fooling around and wasting time watching videos and I was very happy. Do more vid's..

Download Electrodroid on Play Store….Thank me later

No I donโt remember ur last video

Why is this in my recommended in 2019

Repeal OHM's Law. Repeal OHM;s Law!

Resistor color calculator. I dreamed of one in 1969 when I studied this stuff

How many amps can you put thru a resistor? Lets say I have a 1,000 watt resistor. can I put 1,000 amps at 1 volt? Is there something that determines the amperage a resistor can take other then power?

I just bought a 2,000 watt 100 ohm resistor. I'm using it at work to generate 3 amps on a 300 volt power supply. I was just curious if there was an amperage limit because the terminals are not beef nor is the size of the wire that is wound.

ya electrons like to flow away from electrons

Great content for the beginners! โ๏ธ

What a nice explanation too good, You have a great knowledge in yours field , please keep it up ๐๐๐๐๐๐๐๐๐๐

I just want to stop the hyperflashing of my LED taillights…

You like torturing LEDs, aren't you.

I need a resistor for my head it's getting fryed

thanks from Egypt ๐๐

Well done. Thank you for your concise explanations.

can someone explain/link me a video to why the resistor was smoking at the end there?

Wow its amazing

Good video for the basics of electricity. I'm a HVAC Contractor and a lot of technicians don't understand electricity like they should in the electrical and HVAC industry. Hell I have asked electricians what actually make breakers trip and all they can say is heat or over current. Both are right, but they don't understand the concept and internal components.

Ok, guess i know now why i cant get four white leds to light up using two AA batteries.

Came to learn about current, ended learning about voltage drop.

I have leart many from your video thanks bro

this vedio cleared all my concepts feeling that i have acquired extreme knowledge

i m very thankful to you ๐๐๐๐๐๐

hi, first of all thank you for your video, it's very helpful, as many other here I'm just a beginner so that might be a stupid question, but what if I want to light up let's say 6 led of different colours, what would be the ideal resistance, current and power supply?

thank you

Resistance is futile…………

ุดูุฑุง ูู

Resistance is futile

thanks sir very usefull

Very Well explanations.Happy to get onboard

wow very interested,Good luck.and please i have a question

what a legend

3:51 ๐

Love the way you explain things. Very useful

Always so well explained. Thank you!

it's videos like these that make me second guess why I'm in college learning this stuff when amazing people like you explain it so much more thoroughly than any of my professors ever could, and it 's their JOB.

I remember experimenting to prove Ohm's law for 'O' level physics.

Then we went on to 'A' level, and the teacher pointed out that the experiments were worthless, because the meters we used to prove Ohms law themselves relied on Ohm's law..

(Yes, you CAN prove Ohm's law, but you have to be careful what tools you use to do it.)

Use a color calculator, really. 5 seconds on using the color charts would have earned much more credibility to this guy. Decent video otherwise.

@Afrotechmods. Just a couple quick question. Does it matter if we connect the resistor to the positive or the negative cable? If it does, which is the recommended practice?

I donโt get one thing at the start of the video you mentioned the resistance or โbumpingโ causes loss of heat energy due to which bulbs light up so why at the end of the video the LED became dimmer when the resistance was high? Doesnโt high resistance means loss of more amount of heat energy so it should be brighter

watt are you talking about ?

Thank u

Keep going

Great video – new use for old carrots! ๐

Great video

I have a question… I want to connect 3.7v 2500mah lithium ion to a circuit which needs 100 r 200mah what to use to step down the current….

At 8:35, why is the resistor on the cathode side of the circuit? At 7:00, the resistor is is on the anode leg. I am a rookie at this.

Oh my God! Thanks so much for that comic! Everything makes sense now.

Hole flow sucks

Is it possible to reduce the charge speed of a phone by adding a resistor inbetween the charge and the phone? It reduces the voltage as well, does it?

You are a hero!

I could smeel that smoke from my phone screen.

Thanks

What if a motor ,without any further load, is used in a simple circuit with a resistor, what would happen? How much current will the motor be needing?