An ah-ha moment for me was when I was messing with an inductor placed before a capacitor, current flow controlled by a toggle, split directly from the inductor to the ground with a resistor. The resistor there was rated high and I noticed an led in the circuit began to fluctuate in brightness instead of staying lit with the toggle. Watching the amperage showed that, to me anyway, there's almost a fluid dynamic involved with the flow of electrons. This helped me realize why a resistor after an led works. It's like having a river pass through a delicate watermill wheel that is only built for a certain speed and volume of water. You can control the 'speed' and 'volume' of the flow before or after the 'wheel' just as long as the 'water' reaching the wheel isn't so much it 'floods' it. I realize this analogy isn't totally accurate to how electricity works, but it's pretty comparable.
I came to this video after watching your video on how to use a breadboard (fantastic BTW). I thought the same as a lot of people in that the resistance had to be before the LEDs positive to prevent damage (obviously after the first electrical cycle it would be fine). Your explanation was so well executed, and explanation was clear. Thank you
the way i envisioned it is that the flow of electricity is like a bicycle chain and you can put your hand anywhere along this chain to slow it down just like you can put a resistor anywhere before or after the led
I still can't visualize this in my head. If we use the good ol' water analogy, then the resistors are reducing the amount of water going into the LED (thus sparing its life). But if the LED is placed first then in my head, it would only make sense that the LED would get filled with water (and exploding it) before the water would go through the resistor and then be reduced. Needless to say, I am a total noob and am just getting started with this stuff.
Hi - you have to be careful with the water analogy, because while it can be useful sometimes, it is not perfect and electricity does not literally behave like water. If it helps, try thinking of voltage like elevation instead. To keep the math simple, say that a battery provides a voltage of 10 "steps" (so imagine walking up 10 steps). Say that the LED has a voltage "drop" of 6 steps. That means to close the loop and get back down to zero, the resistor would have a voltage "drop" of 4 steps. It does not matter if the resistor is first, then the LED (you go down 4 steps, then 6) or the other way around (you go down 6 steps, then 4). In either case, the "drop" across the LED is still the same. You can also think of it mathematically - the voltages in the circuit are described by the equation V_battery = V_resistor + V_LED. It does not matter if you switch the order of the resistor and LED, that does not change the equation. Again it's the same as writing 10 = 4 + 6 or 10 = 6 + 4 (this comes from something called Kirchoff's Voltage Law, which we do not have our own video on, but you should be able to find plenty on RUclips). Hope that helps!
@@pingupongu843 So the way I understood it, why it works using the resistor before OR after the LED(in series) is that if lets say you are using 9V battery and your LED can take only 5V, that means 4V too much for this LED. Now the way I got it about how the electricity woks is that if you put resistor AFTER the LED the Voltage that will flow through the resistor will be 5V so the battery will also give you 5V even if resistor is placed after. In short, the 9V battery can not output 9V from cathode (positive side +) and then the take in 5V in anode (negative side -) it has to balance it. So if there is resistor and it has limits the current to specific voltage well that is what the batter will output no matter where the resistor is (just be careful this works only in series not in parallel)
its like this if you put the resistor before the LED you're limiting the potential difference but the forward drop(of the LED) is going to be unchanged whether we have the resistor to suppress the voltage or not, but the TOTAL drop across LED will be higher(If there's no resistance) its a lot like the water true but the pressure is too high and not enough water?(or atleast that can flow through it) causing the pipe to rupture or implode. Think of resistances as heads which regulate the pressure differences which cause the current to flow and if there's too much of anything the component is gonna break.
I'm no electrician... but I think of it like this: Imagine you have snow run off from a mountain, all this water collects and speeds up to a point, until it becomes a rushing river (The height of the mountain would equate to the Voltage Start and then when the ground levels off a little on until the point where the water collects into a lake or the ocean - this would be Voltage Finish or 0; and the difference between the two (Voltage Start and Voltage Finish or 0) would be the Voltage Drop). Now if you were to place a huge boulder so that only a small amount of water can get past either side (Resistance) then this would build up and cause the water on BOTH sides to slow down the speed at which the water flows (Current). Thus, it wouldn't matter if you were to place a water wheel generator (load/LED), upstream or down stream from the boulder (Resistor); because the OVERALL speed of the water (Current) on both sides would have slowed down. Or... if you reversed the order of the actions and placed the water wheel generator first (LED); and then placed the boulder (Resistor) second... you get basically the same result. That the water streaming (Current) past the water wheel generator (Load/LED) has slowed down. Which means that the Resistor or LED is not going to be burned out depending on the size or the capacity of the Resistor's resistance rating (Size of the boulder). However if you place the waterwheel first; then you have limited time before it burns out; whereas if you place the boulder first, then you have all the time in the world to place the water wheel. In the above setup, all the components were placed before the power (I'm using the term power loosely and not capitalized; for there is a very definite electronics definition which I'm NOT referring to here) was turned on. Thus... we have three possible ways to set up the experiment: It seems best to set all the components and not switch them in or out WHILE the power is running, or while current is flowing. The current or water flowing is a function of gravity or Potential Kinetic Energy, or simply Potential Energy (Based on the Height of the Mountain/Capacity and Charge of the Battery); the Kinetic Energy is the Current. This isn't a perfect analogy; because you are comparing molecules of water to electrons jumping from atom to atom; but it kind of illustrates the general idea.
So, if I’m understanding this correctly, it appears as though the “water pipe” analogy does NOT apply here, as the presence of a thinner pipe does not reduce the flow of water before it; only after. Or doesn’t it? The water does become somewhat backed-up before the mouth of the thinner pipe, and the flow does gradually become slower at points closer and closer to the water source until the flow is the same rate throughout. So maybe the water analogy DOES work. But there’s that momentary period at which flow is higher before it reaches the thinner pipe; anything in that path will be met with that higher flow briefly. Is that not the case with an electric circuit? Would the LED not be very briefly taking in a higher current before the resistor brings the current down?
Hi - in a closed pipe, the *volumetric flow rate* of the water must remain constant (the volume of water per unit time - so for example measured in something like cubic meters per second or gallons per minute). If you restrict the flow, for example by installing a thinner section of pipe in the middle, that is going to affect the flow rate both upstream and downstream of the restriction. You have to be careful not to get volumetric flow rate mixed up with *velocity*. For example, if you have a hose with the nozzle on the "jet" setting - the velocity of the water is slower inside the hose and faster once it goes through a narrow nozzle and exits the jet, but the volumetric flow of water is the same before and after the nozzle. Volumetric flow rate in this case is analogous to electrical current in a circuit - for a series circuit, the current must be the same everywhere. In this case, the current in the circuit is the same through the LED and the resistor since they are in series. Hope that helps - it's a bit much to explain in a RUclips comment, but there are other videos on RUclips that will provide more of a background on circuit theory that might be helpful in understanding.
"Conventional current" (from positive to negative) was defined before scientists fully understood the actual movement of electrons. The convention is still used in most applications today.
Are there any advantages to doing it a certain way tho? Also, is there a way to get the "lost" amps back after the electricity has gone thorugh the resistor?
As far as the physics of the circuit are concerned, it doesn't really matter. When physically laying the circuit out on the breadboard you may find that you prefer one arrangement over the other. Power dissipated in the resistor is converted to waste heat so it cannot be recovered directly within the circuit.
why some time I find a resistor connected to ground before the load? I read it's a current limiting resistor but I find not connecting it series makes me confused 😕 as I don't know how much does it lower the current.
Hi - a resistor connected to ground could serve different purposes depending on the circuit. There are online forums dedicated to electronics where you might be able to get more help if you can post a link to a specific circuit diagram.
I’m using an in hole resistor inside a car license plate light bulb socket to prevent random turn off of an LED bulb. I have one end of the resistor in contact with one contact inside the socket and the other end of the resistor in contact with the other contact inside the socket. Then I insert the bulb. It seems to be working. My question is: is this resistor connected in parallel as described? Also, if I wanted to connect it to the wires instead of inside the socket could I just connect one end of the resistor to one wire going into the socket and the other end of the resistor to the other wire going into the socket? If I calculated I need a 120 ohm, 1W resistor am I ok to choose a 120 ohm, 2W or a 120 ohm, 5 instead? It is my understanding that the 5W would dissipate more heat so it would be a better choice. Any idea what the operating temperature difference would be between a 2W resistor and a 5W? The LED is rated at 83 mA at 13.2V.
Hi - our channel is for K-12 students doing science projects; we are unable to help with automotive/hobby projects like this but you should be able to find other forums/channels online that can help with your questions.
@@Science.Buddies I’ve posted on about a dozen or more different videos in the last 3 weeks and nobody replies. You’re the first one. To be honest I don’t think anyone knows how to answer it.
We don't have our own video on it (yet), but we recommend searching for videos on "ohm's law" and "LED resistor calculation." The resistor helps prevent the LED from burning out by limiting the amount of current that flows through it.
So at the top in red, its 3V because its relative to ground(0V) right? that is its 3 because its 0+3 = 3V. At least thats what you said and at least thats what I think I understood. / So my question, if the ground node had some other potential instead of 0V (say 15V), then would that red node become 15V+3v=18V?
You're correct! Voltage is a *relative* potential difference between two points. In a battery-powered circuit, we *usually* assume the negative terminal of the battery is defined as ground (0V). Sometimes it's just implied and not explicitly stated. Think of it kind of like elevation - if I say "an elevation of 10,000 feet," you'd generally assume I mean relative to sea level, which we define as 0 feet. However, I could pick another arbitrary reference point to define as "zero" - say something 2,000 feet above sea level. In that case, my original elevation of 10,000 feet is now 8,000 feet relative to my new reference point, and sea level is now -2,000 feet (but those two points are still 10,000 feet apart). This video explains the same concept: ruclips.net/video/Qn9lwFMfO2c/видео.html
Wait, i dont think this is correct, voltage is a DIFFERENCE of potential. With 15v and 3v, voltage will be 12v and the current will flow in the opposit (compared to the example) direction.
Hi Allyn - it depends on the voltage of your power supply. In this case, 2xAA batteries only provides about 3 volts. Since the forward voltage drop over a red LED is usually over 1.5 volts, you can put two of them in series and get away with not using a resistor. However, for example, if you were using a 4xAA battery pack (6 volts) and only put 2 LEDs in series, they would still burn out because the voltage would be too high.
@@Science.Buddies PARDON? "Since the forward voltage drop over a red LED is usually over 1.5 volts" which means the Vf is Greater than 3V and so would NOT light since total Vf > Vcc Red LEDs typically have a Vf of around 1V8
@@Science.Buddies, I was pretty surprised at how fast that LED burned out. I've been playing around with a candle-flicker LED out of a dollar-store LED candle that used a single 3V button cell battery. I used two 3V cells and it didn't even seem a lot brighter. But that also (probably) uses a PWM circuit which would certainly reduce the heat the LED needs to dissipate, right? (I'm still VERY new to the whole electronics thing, so I'm really just guessing here.)
@@MyName-tb9oz Even though they provide the same voltage as 2xAA batteries, button cell batteries generally provide a much lower current. As a result, it's usually safe to connect an LED to them directly with no resistor. For example, see our LED stickies project: www.sciencebuddies.org/stem-activities/LED-stickies?from=RUclips. If you're new to electronics and want to learn more, Google "battery internal resistance." Batteries can have the same no-load voltage but different internal resistances, which affects the amount of current they can provide. Hope that helps!
An ah-ha moment for me was when I was messing with an inductor placed before a capacitor, current flow controlled by a toggle, split directly from the inductor to the ground with a resistor. The resistor there was rated high and I noticed an led in the circuit began to fluctuate in brightness instead of staying lit with the toggle. Watching the amperage showed that, to me anyway, there's almost a fluid dynamic involved with the flow of electrons. This helped me realize why a resistor after an led works.
It's like having a river pass through a delicate watermill wheel that is only built for a certain speed and volume of water. You can control the 'speed' and 'volume' of the flow before or after the 'wheel' just as long as the 'water' reaching the wheel isn't so much it 'floods' it. I realize this analogy isn't totally accurate to how electricity works, but it's pretty comparable.
I came to this video after watching your video on how to use a breadboard (fantastic BTW). I thought the same as a lot of people in that the resistance had to be before the LEDs positive to prevent damage (obviously after the first electrical cycle it would be fine). Your explanation was so well executed, and explanation was clear. Thank you
Thanks! That's exactly why we made this video.
the way i envisioned it is that the flow of electricity is like a bicycle chain and you can put your hand anywhere along this chain to slow it down just like you can put a resistor anywhere before or after the led
I still can't visualize this in my head. If we use the good ol' water analogy, then the resistors are reducing the amount of water going into the LED (thus sparing its life). But if the LED is placed first then in my head, it would only make sense that the LED would get filled with water (and exploding it) before the water would go through the resistor and then be reduced. Needless to say, I am a total noob and am just getting started with this stuff.
Hi - you have to be careful with the water analogy, because while it can be useful sometimes, it is not perfect and electricity does not literally behave like water. If it helps, try thinking of voltage like elevation instead. To keep the math simple, say that a battery provides a voltage of 10 "steps" (so imagine walking up 10 steps). Say that the LED has a voltage "drop" of 6 steps. That means to close the loop and get back down to zero, the resistor would have a voltage "drop" of 4 steps. It does not matter if the resistor is first, then the LED (you go down 4 steps, then 6) or the other way around (you go down 6 steps, then 4). In either case, the "drop" across the LED is still the same. You can also think of it mathematically - the voltages in the circuit are described by the equation V_battery = V_resistor + V_LED. It does not matter if you switch the order of the resistor and LED, that does not change the equation. Again it's the same as writing 10 = 4 + 6 or 10 = 6 + 4 (this comes from something called Kirchoff's Voltage Law, which we do not have our own video on, but you should be able to find plenty on RUclips). Hope that helps!
@@Science.Buddies Ok cool that certainly helps! Thank you so much for the reply and ofcourse the video!
@@pingupongu843 So the way I understood it, why it works using the resistor before OR after the LED(in series) is that if lets say you are using 9V battery and your LED can take only 5V, that means 4V too much for this LED. Now the way I got it about how the electricity woks is that if you put resistor AFTER the LED the Voltage that will flow through the resistor will be 5V so the battery will also give you 5V even if resistor is placed after.
In short, the 9V battery can not output 9V from cathode (positive side +) and then the take in 5V in anode (negative side -) it has to balance it. So if there is resistor and it has limits the current to specific voltage well that is what the batter will output no matter where the resistor is (just be careful this works only in series not in parallel)
its like this if you put the resistor before the LED you're limiting the potential difference but the forward drop(of the LED) is going to be unchanged whether we have the resistor to suppress the voltage or not, but the TOTAL drop across LED will be higher(If there's no resistance) its a lot like the water true but the pressure is too high and not enough water?(or atleast that can flow through it) causing the pipe to rupture or implode. Think of resistances as heads which regulate the pressure differences which cause the current to flow and if there's too much of anything the component is gonna break.
Hell yeah, you answered my questions, thanks bro!
I already knew that the order don't mater, but didn't have a comprehensive explanation. Thank you for the later.
You're welcome!
It often confuses people when it is said that the resistor DROPS voltage. It is better to say, in this case, that there is voltage ACROSS the resistor
It should be said that the resistor absorbs some current therefore lowering the voltage?
@@nuovoaccount998 lol no
@@kennmossman8701 elaborate
@@nuovoaccount998 laughing out loud
@@kennmossman8701 on why "no lol"
Great explanation, Thank-you!
This was great. Thank you.
I'm no electrician... but I think of it like this:
Imagine you have snow run off from a mountain, all this water collects and speeds up to a point, until it becomes a rushing river (The height of the mountain would equate to the Voltage Start and then when the ground levels off a little on until the point where the water collects into a lake or the ocean - this would be Voltage Finish or 0; and the difference between the two (Voltage Start and Voltage Finish or 0) would be the Voltage Drop).
Now if you were to place a huge boulder so that only a small amount of water can get past either side (Resistance) then this would build up and cause the water on BOTH sides to slow down the speed at which the water flows (Current). Thus, it wouldn't matter if you were to place a water wheel generator (load/LED), upstream or down stream from the boulder (Resistor); because the OVERALL speed of the water (Current) on both sides would have slowed down. Or... if you reversed the order of the actions and placed the water wheel generator first (LED); and then placed the boulder (Resistor) second... you get basically the same result. That the water streaming (Current) past the water wheel generator (Load/LED) has slowed down. Which means that the Resistor or LED is not going to be burned out depending on the size or the capacity of the Resistor's resistance rating (Size of the boulder).
However if you place the waterwheel first; then you have limited time before it burns out; whereas if you place the boulder first, then you have all the time in the world to place the water wheel.
In the above setup, all the components were placed before the power (I'm using the term power loosely and not capitalized; for there is a very definite electronics definition which I'm NOT referring to here) was turned on.
Thus... we have three possible ways to set up the experiment: It seems best to set all the components and not switch them in or out WHILE the power is running, or while current is flowing. The current or water flowing is a function of gravity or Potential Kinetic Energy, or simply Potential Energy (Based on the Height of the Mountain/Capacity and Charge of the Battery); the Kinetic Energy is the Current.
This isn't a perfect analogy; because you are comparing molecules of water to electrons jumping from atom to atom; but it kind of illustrates the general idea.
So, if I’m understanding this correctly, it appears as though the “water pipe” analogy does NOT apply here, as the presence of a thinner pipe does not reduce the flow of water before it; only after. Or doesn’t it? The water does become somewhat backed-up before the mouth of the thinner pipe, and the flow does gradually become slower at points closer and closer to the water source until the flow is the same rate throughout. So maybe the water analogy DOES work.
But there’s that momentary period at which flow is higher before it reaches the thinner pipe; anything in that path will be met with that higher flow briefly. Is that not the case with an electric circuit? Would the LED not be very briefly taking in a higher current before the resistor brings the current down?
Hi - in a closed pipe, the *volumetric flow rate* of the water must remain constant (the volume of water per unit time - so for example measured in something like cubic meters per second or gallons per minute). If you restrict the flow, for example by installing a thinner section of pipe in the middle, that is going to affect the flow rate both upstream and downstream of the restriction. You have to be careful not to get volumetric flow rate mixed up with *velocity*. For example, if you have a hose with the nozzle on the "jet" setting - the velocity of the water is slower inside the hose and faster once it goes through a narrow nozzle and exits the jet, but the volumetric flow of water is the same before and after the nozzle. Volumetric flow rate in this case is analogous to electrical current in a circuit - for a series circuit, the current must be the same everywhere. In this case, the current in the circuit is the same through the LED and the resistor since they are in series. Hope that helps - it's a bit much to explain in a RUclips comment, but there are other videos on RUclips that will provide more of a background on circuit theory that might be helpful in understanding.
Question: shouldn’t the current (yellow arrow) be following the electron flow? (from negative terminal to positive terminal)
"Conventional current" (from positive to negative) was defined before scientists fully understood the actual movement of electrons. The convention is still used in most applications today.
Are there any advantages to doing it a certain way tho? Also, is there a way to get the "lost" amps back after the electricity has gone thorugh the resistor?
As far as the physics of the circuit are concerned, it doesn't really matter. When physically laying the circuit out on the breadboard you may find that you prefer one arrangement over the other. Power dissipated in the resistor is converted to waste heat so it cannot be recovered directly within the circuit.
@@Science.Buddies Thank you for the fast reply, appreciate it!
why some time I find a resistor connected to ground before the load?
I read it's a current limiting resistor but I find not connecting it series makes me confused 😕 as I don't know how much does it lower the current.
Hi - a resistor connected to ground could serve different purposes depending on the circuit. There are online forums dedicated to electronics where you might be able to get more help if you can post a link to a specific circuit diagram.
Can I have a resistor before the led and 1 after. For example 220 before and 100 after instead of 1 that is 330 ?
Good video btw. Thanks
Yes, if you have more than one resistor you could put both of them before, both after, or one after and one before. Great question!
I’m using an in hole resistor inside a car license plate light bulb socket to prevent random turn off of an LED bulb. I have one end of the resistor in contact with one contact inside the socket and the other end of the resistor in contact with the other contact inside the socket. Then I insert the bulb. It seems to be working. My question is: is this resistor connected in parallel as described? Also, if I wanted to connect it to the wires instead of inside the socket could I just connect one end of the resistor to one wire going into the socket and the other end of the resistor to the other wire going into the socket? If I calculated I need a 120 ohm, 1W resistor am I ok to choose a 120 ohm, 2W or a 120 ohm, 5 instead? It is my understanding that the 5W would dissipate more heat so it would be a better choice. Any idea what the operating temperature difference would be between a 2W resistor and a 5W? The LED is rated at 83 mA at 13.2V.
Hi - our channel is for K-12 students doing science projects; we are unable to help with automotive/hobby projects like this but you should be able to find other forums/channels online that can help with your questions.
@@Science.Buddies I’ve posted on about a dozen or more different videos in the last 3 weeks and nobody replies. You’re the first one. To be honest I don’t think anyone knows how to answer it.
You may have better luck with forums dedicated to electronics, like something on Reddit or Stackexchange, as opposed to RUclips comments. Good luck!
Great explanation! I was wondering, when does the position of the resistor in reference to the LED matter?
We're not aware of any situations where it does matter - you can just swap them!
If I put the resistors before and after the led, how to calculate the current? And also what's the benefits using this circuit?
We don't have our own video on it (yet), but we recommend searching for videos on "ohm's law" and "LED resistor calculation." The resistor helps prevent the LED from burning out by limiting the amount of current that flows through it.
So at the top in red, its 3V because its relative to ground(0V) right? that is its 3 because its 0+3 = 3V. At least thats what you said and at least thats what I think I understood.
/
So my question, if the ground node had some other potential instead of 0V (say 15V), then would that red node become 15V+3v=18V?
You're correct! Voltage is a *relative* potential difference between two points. In a battery-powered circuit, we *usually* assume the negative terminal of the battery is defined as ground (0V). Sometimes it's just implied and not explicitly stated. Think of it kind of like elevation - if I say "an elevation of 10,000 feet," you'd generally assume I mean relative to sea level, which we define as 0 feet. However, I could pick another arbitrary reference point to define as "zero" - say something 2,000 feet above sea level. In that case, my original elevation of 10,000 feet is now 8,000 feet relative to my new reference point, and sea level is now -2,000 feet (but those two points are still 10,000 feet apart). This video explains the same concept: ruclips.net/video/Qn9lwFMfO2c/видео.html
@@Science.Buddies thanks so much
Wait, i dont think this is correct, voltage is a DIFFERENCE of potential. With 15v and 3v, voltage will be 12v and the current will flow in the opposit (compared to the example) direction.
Apart from the math theory, still doesn't make any sense. There has to be something else that's going on here.
So can you use 2 LEDs in series without any resistors?
No. A resistor limits the current through an LED. Even if you have 2 of them, you'll need something to limit the current.
Hi Allyn - it depends on the voltage of your power supply. In this case, 2xAA batteries only provides about 3 volts. Since the forward voltage drop over a red LED is usually over 1.5 volts, you can put two of them in series and get away with not using a resistor. However, for example, if you were using a 4xAA battery pack (6 volts) and only put 2 LEDs in series, they would still burn out because the voltage would be too high.
@@Science.Buddies PARDON? "Since the forward voltage drop over a red LED is usually over 1.5 volts" which means the Vf is Greater than 3V and so would NOT light since total Vf > Vcc Red LEDs typically have a Vf of around 1V8
@@Science.Buddies, I was pretty surprised at how fast that LED burned out. I've been playing around with a candle-flicker LED out of a dollar-store LED candle that used a single 3V button cell battery. I used two 3V cells and it didn't even seem a lot brighter. But that also (probably) uses a PWM circuit which would certainly reduce the heat the LED needs to dissipate, right? (I'm still VERY new to the whole electronics thing, so I'm really just guessing here.)
@@MyName-tb9oz Even though they provide the same voltage as 2xAA batteries, button cell batteries generally provide a much lower current. As a result, it's usually safe to connect an LED to them directly with no resistor. For example, see our LED stickies project: www.sciencebuddies.org/stem-activities/LED-stickies?from=RUclips. If you're new to electronics and want to learn more, Google "battery internal resistance." Batteries can have the same no-load voltage but different internal resistances, which affects the amount of current they can provide. Hope that helps!
mmmmmmmmmmm You do know that in a schematic a single cell symbol implies just 1V5?