I'm a newbie trying to learn, so go easy on me.
I'm having a difficult time reconciling in my mind why current in a simple DC-series circuit with two resistors of differing values is not determined solely by the highest Ohm-value resistor. For example, if a simple DC circuit has a battery of 100V and a resistor of 20 Ohms, the current is 5.0A. If you then insert a 10 Ohm resistor in series (which by itself would yield a current of 10.0A) the current drops to 3.3A. It seems like, if I imagine the charge carriers being passed along the chain, that once they get through the 20 Ohm resistor that they should be able to maintain that "speed" because the charge carriers would be coming out of the 20 Ohm resistor at a slower rate then they would be going into the 10 Ohm resistor. So, the 10 Ohm resistor would always be waiting for the next charge carrier and would not bring the speed down any lower. The classic water and pipes analogy doesn't help as it would seem to reach the same conclusion.
I know I'm missing something obvious here.
Thanks for helping.
I'm having a difficult time reconciling in my mind why current in a simple DC-series circuit with two resistors of differing values is not determined solely by the highest Ohm-value resistor. For example, if a simple DC circuit has a battery of 100V and a resistor of 20 Ohms, the current is 5.0A. If you then insert a 10 Ohm resistor in series (which by itself would yield a current of 10.0A) the current drops to 3.3A. It seems like, if I imagine the charge carriers being passed along the chain, that once they get through the 20 Ohm resistor that they should be able to maintain that "speed" because the charge carriers would be coming out of the 20 Ohm resistor at a slower rate then they would be going into the 10 Ohm resistor. So, the 10 Ohm resistor would always be waiting for the next charge carrier and would not bring the speed down any lower. The classic water and pipes analogy doesn't help as it would seem to reach the same conclusion.
I know I'm missing something obvious here.
Thanks for helping.
Thanks for you replies but I think I need to clarify my question a little. I understand that they are additive and that effectively there is just one resistor @ 30 Ohms.
But on an atomic level the electrons physically go through one resistor first, then a lead/wire connector, then the next resistor. Right? If so, and I picture atoms passing one electron at a time such that they can't pass one until the next atom in the chain is ready to accept (sort of like a firemen bucket brigade), then the atoms in the 10 ohm resistor must pass them faster than the ones in the 20 ohm resistor. Then, if the flow is such that the electrons go through the 20 ohm resistor first, isn't it's output slower than the 10 ohm's input?
One thought I just had is: "Is it because the voltage is lower after the 20 Ohm resistor and therefore the "pushing" pressure isn't as great on the 10 Ohm?"
I know Ohm's Law is a correct but I'm just struggling to understand at the lowest level. That's probably my mistake as I'm not that bright.
Anyway, if you can think of another way to explain it such that it gets through my thick head I would appreciate it.
Thanks
But on an atomic level the electrons physically go through one resistor first, then a lead/wire connector, then the next resistor. Right? If so, and I picture atoms passing one electron at a time such that they can't pass one until the next atom in the chain is ready to accept (sort of like a firemen bucket brigade), then the atoms in the 10 ohm resistor must pass them faster than the ones in the 20 ohm resistor. Then, if the flow is such that the electrons go through the 20 ohm resistor first, isn't it's output slower than the 10 ohm's input?
One thought I just had is: "Is it because the voltage is lower after the 20 Ohm resistor and therefore the "pushing" pressure isn't as great on the 10 Ohm?"
I know Ohm's Law is a correct but I'm just struggling to understand at the lowest level. That's probably my mistake as I'm not that bright.
Anyway, if you can think of another way to explain it such that it gets through my thick head I would appreciate it.
Thanks
Imagine a piece of resistance wire long enough to make a 30ohm resistor. It is easy with ohms law to accept that this will tak 3.3A from 100V.
Now cut the wire one third of the way along you then have a 10ohm and a 20ohm resistor, if you join the two cut ends together you then remake the 30ohms, but this time it is made of a 10+20 in series.
The wire when passing 3.3 amps will drop a given voltage for each unit length, and this will be regardless of the length used.
The 20ohm resistor will drop 66V at 3.3A and the 10ohm 33V, when added together these add up to the 100V.
OTH
Chris
Now cut the wire one third of the way along you then have a 10ohm and a 20ohm resistor, if you join the two cut ends together you then remake the 30ohms, but this time it is made of a 10+20 in series.
The wire when passing 3.3 amps will drop a given voltage for each unit length, and this will be regardless of the length used.
The 20ohm resistor will drop 66V at 3.3A and the 10ohm 33V, when added together these add up to the 100V.
OTH
Chris
Hi,
I'm not a physicist but I'll try to help.
At the electron level, trillions of electrons are floating about in a random cloud. Apply a voltage and then the cloud of electrons move in unison (i.e. all at the same time) to dissipate the driving voltage. That random cloud moving is the intrinsic noise in a perfect resistor and the unison movement is the current that we negatively measure. The electrons bump into things along the way & that is the heat we can feel.
Someone come in and help me!
I'm not a physicist but I'll try to help.
At the electron level, trillions of electrons are floating about in a random cloud. Apply a voltage and then the cloud of electrons move in unison (i.e. all at the same time) to dissipate the driving voltage. That random cloud moving is the intrinsic noise in a perfect resistor and the unison movement is the current that we negatively measure. The electrons bump into things along the way & that is the heat we can feel.
Someone come in and help me!
That sounds about right. It's the 'bumping into things' that really makes resistors resist, turning electrical energy into heat. The more resistors you put in series, the more things there are for electrons to bump into, causing them to lose more energy along the way, reducing the current for a given voltage.
if you put a valve on a waterpipe, the valve has a resistance, water pressure before the valve is higher than after it.
If the valve is placed there for that purpose it is called a choke, pressure is choked.
waterparticles bump into eachother, loosing kinetic energy transformed to heat.
The water looses energy passing the choke, place several choke valves behind eachother, the water will have no pressure, no energy left.
A turbine engine has several rotor stages.
After passing each rotor the gasses passing through the turbine have lower pressure, lower energy.
In the ideal turbine engine residual energy from gasses exiting the turbine is zero.
Why has a thin thread more resistance, because the same electrons need to pass through a smaller passage. They interact and loose energy.
If the valve is placed there for that purpose it is called a choke, pressure is choked.
waterparticles bump into eachother, loosing kinetic energy transformed to heat.
The water looses energy passing the choke, place several choke valves behind eachother, the water will have no pressure, no energy left.
A turbine engine has several rotor stages.
After passing each rotor the gasses passing through the turbine have lower pressure, lower energy.
In the ideal turbine engine residual energy from gasses exiting the turbine is zero.
Why has a thin thread more resistance, because the same electrons need to pass through a smaller passage. They interact and loose energy.
cfitzger said:
The phenomenon you describe might make more sense in a paralell connection scenario. The lower resistance will pass more voltage.... i.e will dominate the circuit more. In a series connection its the opposite, the larger resistance determines more of the circuit's character/ output voltage.
See what you made me do Jacco? reply seriously... !
I think this is where the problem is. None are faster..or slower. They are all pretty much the speed of light with the exception of the ones that are stopped and 'burned up'. The 20 ohm resistor simply burns off twice as many as the 10 ohm..
hum, correct me if I am wrong.
Does anyone really know the way this works at the lowest level? Isn't it mostly theory?
Yes speed is definitely the limiting factor in your understanding. If you have a circuit with just a wire and a light on an end, and a circuit with a resistor before that light, flicking on the switch will cause the light to turn on with the same delay (assuming this delay is easily measurable).
In other words, electricity travels same speed no matter what resistance its flowing through.
What you have to imagine this as is the following. A wire is a conductive material. It thus has free electrons that are easily separated from its atoms (this is what makes metals conductive and other elements not). So you have this "pipe" of free electrons in your wire that are packed in super close to eachother. The instant you apply a voltage to the wire, you are forcing new electrons (ex. from a battery) into the wire, these electrons will force the electrons in the entrance of your wire down, which in turn will force its neighbouring electrons down and this goes on in a chain reaction.
Picture a group of people sitting around a round table continuously switching seats to the right. There is one person standing behind one seat, checking if there is movement. The second the person in the seat infront of him moves, he will put his hand up. Now realise that no matter who moves first on the table, the man's arm will go up right away, since everyone is forced to move. The man is the light that turns on when the circuit is closed.
Inside a wire, there are more than one row of seats. So there are many possible seats for the electrons to get bumped into when forced out of theirs. The lower guage your wire is, the less openings there are, and the less CURRENT flows at once as electrons must "wait" to flow into the wire, but the bumping always occurs at the same speed.
An interesting note, is that electrons actually flow very slowly around a circuit. the speed, if i remember correclty, is dependant of the material and cross section area. Its not unreasonable for an electron leaving a battery to take more than 20 minutes to make it through the light in a small circuit of a few cms. The speed of electricity comes from the chain reaction, which is yes, about the speed of light.
In other words, electricity travels same speed no matter what resistance its flowing through.
What you have to imagine this as is the following. A wire is a conductive material. It thus has free electrons that are easily separated from its atoms (this is what makes metals conductive and other elements not). So you have this "pipe" of free electrons in your wire that are packed in super close to eachother. The instant you apply a voltage to the wire, you are forcing new electrons (ex. from a battery) into the wire, these electrons will force the electrons in the entrance of your wire down, which in turn will force its neighbouring electrons down and this goes on in a chain reaction.
Picture a group of people sitting around a round table continuously switching seats to the right. There is one person standing behind one seat, checking if there is movement. The second the person in the seat infront of him moves, he will put his hand up. Now realise that no matter who moves first on the table, the man's arm will go up right away, since everyone is forced to move. The man is the light that turns on when the circuit is closed.
Inside a wire, there are more than one row of seats. So there are many possible seats for the electrons to get bumped into when forced out of theirs. The lower guage your wire is, the less openings there are, and the less CURRENT flows at once as electrons must "wait" to flow into the wire, but the bumping always occurs at the same speed.
An interesting note, is that electrons actually flow very slowly around a circuit. the speed, if i remember correclty, is dependant of the material and cross section area. Its not unreasonable for an electron leaving a battery to take more than 20 minutes to make it through the light in a small circuit of a few cms. The speed of electricity comes from the chain reaction, which is yes, about the speed of light.
speed
Hi.
The electrons in a cable or resistor move very slowly (well compared the the speed of light) only a few meters per second if the wire is of the correct guage.
Imagine a long thin tube full of beads, if you push an extra beed in one end then a bead will pop out of the othe end instantaniously, but the individual beads move very little, the bead out of the end is not the same one you put in.
Now for resistance, if the tube is thinner then it will take more force to push a given number of beads a minute through the tube, the beads will have to move faster and will have more friction. The tube will warm up with the friction of the beads.
This is what happens in a resistor or wire, as the electron jump from atom to atom they use energy (supper conductors are another thing) this energy loss is the resistance and is what causes the wire to warm up if too high a current is used. In a purpose made resister, there are less atoms with available electrons to pass the signal so the electons need a higher voltage to drive them from one atom to the next and when they reach there they are going faster and generate more heat.
This is a bit of a rough explination but it's early morning and i need another cup of tea, but i hope it helps.
Chris
Hi.
The electrons in a cable or resistor move very slowly (well compared the the speed of light) only a few meters per second if the wire is of the correct guage.
Imagine a long thin tube full of beads, if you push an extra beed in one end then a bead will pop out of the othe end instantaniously, but the individual beads move very little, the bead out of the end is not the same one you put in.
Now for resistance, if the tube is thinner then it will take more force to push a given number of beads a minute through the tube, the beads will have to move faster and will have more friction. The tube will warm up with the friction of the beads.
This is what happens in a resistor or wire, as the electron jump from atom to atom they use energy (supper conductors are another thing) this energy loss is the resistance and is what causes the wire to warm up if too high a current is used. In a purpose made resister, there are less atoms with available electrons to pass the signal so the electons need a higher voltage to drive them from one atom to the next and when they reach there they are going faster and generate more heat.
This is a bit of a rough explination but it's early morning and i need another cup of tea, but i hope it helps.
Chris
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