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jackorocko
- Apr 4, 2010
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resist not only sounds better but it describes the physical nature of the resistor to the electron. AFAIK resistors oppose the flow of electrons which in turn cause a voltage drop and produces heat as a bi-product. The electrons aren't confined or limited in anyway and they do not disappear.
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A resistor, does not resist /oppose the electrons flowing through a resistor though, if it did the name would make sense, if it did do that, all resistors would get hot from even the smallest amounts of current...
Think about it this way, if i stick my foot in the door, now i'm 'resisting' you from closing the door and energy is wasted, the resistor does not do this kind of job at all, there really is no resistance taking place...
what's happening is that the resistor is not conductive enough to allow the electrons to flow through the resistor, so it restricts the current... think of it like this imagine a 100amp/h battery place a 'resistor' of 1k, if that resistor had to 'resist' the current from the battery it would have to tolerate a lot of heat...
imagine 100k ohm resistor on 1amp circuit rated at only 1/8th of a watt, if it had to resist the current it would die... instead the resistor is only capable of supplying a little amount of current, so it restricts the current, not resist the current...
No, it resists the flow of current.
A jfet with the gate tied to the source will restrict current -- i.e. it will prevent the current from rising above a certain value until the device is destroyed.
A resistor will resist the flow of electrons, the amount the flow through is dependent on the pressure (voltage) and the resistance.
People *think* that resistors somehow restrict current and they ask for a resistor to do something as if it had some special regulating properties.
It's a bit of a pointless issue though. Nobody's going to be changing their name any time soon.
If you stick your foot in the door, your doing more than resisting, you're effectively inserting a barrier -- like an insulator. However if nothing is moving, no energy is wasted.
And a 100k 1/8w resistor carrying 1A WOULD die, probably in an incandescent and almost pyrotechnic way. And a resistor supplies no current -- current flows through it.
A jfet with the gate tied to the source will restrict current -- i.e. it will prevent the current from rising above a certain value until the device is destroyed.
A resistor will resist the flow of electrons, the amount the flow through is dependent on the pressure (voltage) and the resistance.
People *think* that resistors somehow restrict current and they ask for a resistor to do something as if it had some special regulating properties.
It's a bit of a pointless issue though. Nobody's going to be changing their name any time soon.
If you stick your foot in the door, your doing more than resisting, you're effectively inserting a barrier -- like an insulator. However if nothing is moving, no energy is wasted.
And a 100k 1/8w resistor carrying 1A WOULD die, probably in an incandescent and almost pyrotechnic way. And a resistor supplies no current -- current flows through it.
Size -- seriously.
Bigger = more surface area = able to dissipate more heat.
For a given type of resistor, at it's rated power it's surface temperature will be very similar. There are some complicating factors like that the volume is proportional to the cube of the size and the area to the square of the size, but that is just detail unless you're a manufacturer.
Bigger = more surface area = able to dissipate more heat.
For a given type of resistor, at it's rated power it's surface temperature will be very similar. There are some complicating factors like that the volume is proportional to the cube of the size and the area to the square of the size, but that is just detail unless you're a manufacturer.
Resqueline
- Jul 31, 2009
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I believe the term restrictor/restriction is use in pneumatics and hydraulics, where it serves the same purpose/function as a resistor in electronics.
But I see no point in changing/debating the electronic term however, the present term seems very applicable/descriptive to me as it is.
Resistor power: what Steve said. Also, of course; metal & ceramic stands higher temperatures and can therefore dissipate more power than carbon & varnish can do.
But I see no point in changing/debating the electronic term however, the present term seems very applicable/descriptive to me as it is.
Resistor power: what Steve said. Also, of course; metal & ceramic stands higher temperatures and can therefore dissipate more power than carbon & varnish can do.
What's the difference between a 1/2watt resistor and a 5watt resistor, what exactly changes in the resistor? physically....
don't say sizeseriously, what changes to make it withstand the heat?
size as Steve said is true !
but more commonly anything resistor rated at over 2 Watts will normally be a wirewound one rather than carbon or metal film
Dave
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ok, so what's the difference between AWG (american wire gauge? off the top of my head) basically, inside the insulated wire you have hair thin strands of copper, it's never solid it's always intertwined...
now 100meters of intertwined copper wire which let's say is rated at 5amps good for small DIY jobs...
let's suppose the wire had an internal resistance of 100ohms, i have no clue actually i'm not going to look it up, and your 100 ohm resistor 50watt resistor sitting right next to the 100 meter cable, is it fair to say that in this instance both the Resistor and the huge length of wire are both doing the same thing.....
what is that exactly? both create a voltage drop, both have a resistance of 100ohms, yet how is the write 'resisting' the electrons the same way a resister does? or is it different?
on a side note, take your typical AWG chart and simply remove 1 copper intertwined strand, and allow 1 amp to flow though it, you'll get burnt so quickly if your did that, and yet with the length long enough it too could stop itself from being burnt out from a length resulting in only a hand full of ohms...
so a resistor to me is something that does not allow electrons to flow as easy as it would like (as indeed any material scaled up, including metals)... take a lead pencil scribble onto paper a nice square patch of lead, cake it on, right now with a 9v battery take the cathode and place the pin against a corner of the lead drawn scribble you just made, now take the other pen and place it against the lead, obviously you need to complete the circuit..
LED + ------[~~~~~~~~~~]------------ - LED - -Battery
basically, an LED in series with the 9 volt battery and your paper made 'resister' i don't agree with the analogy is all, a resistor no more 'resists' the flow of electrons than a piece of toast dipped in mercury...
how imagine it to work is like this...
the electrons travel at the speed of light when released from their other states of matter, eg chemically, electrochemically, photovoltaic, as the energy states move up and down, eg from photon to electron.., either way however the magnetic field is induced and captured these electrons can be manipulated to follow paths, the paths they go through are the ones with least resistance..
feel free to correct me if i'm wrong, but i'd like to show people may way of thinking regardless of how wrong i am here
however, if more electrons try to go through the semi conductor or conductor than the circuit, wire can handle, the electrons will become squeezed and no longer have any where to travel so they become heat as a side product, take 1 strand of wire and allow a few amps to flow, it will turn red hot and die and melt, you could even use a penny coin as a resistor....
So what's going on the resistor/any conductive object... well imagine fragmented pieces of metal, or metal conduits like a sewer system, now, you simply use any material that has a high resistance value, nichrome wire for example if not as a resistor it's found in electric blankets. use thicker wire and the blanket would cease to become hot....
So you say a bigger resistor has bigger heatsink, no i disagree, instead it's scaled up the impurities used in the resistor are bigger, the heat sink will still be in portion, simply larger and wider the conductor it is, more current will flow, hence when a 1million ohm resistor will quite gladly be connected to 240 volts and there would not be enough current to power an LED.
Ceramic has a high resistance value and can withstand the heat better, but you're not going to have /less/ heat it will be the same heat except Ceramic can tolerate the heat better than conventional resistors.
So a resistor /resists/ energy, it resists it no more than anything else on the planet that has some conductivity..
100ohm resistor or 100ohms of ceramic cut, you can dope anything none conductive like silicon with tiny amounts of impurities that allow it to conduct eg semiconductors and silicon.and arsenic and phosphorous... safe even on large scale.
so why use wire, why not just say wire as a resistor, oh yes, you need to roll up 300 meters to use it as a capacitor though lol, heat is only a by product if there's simply not enough conductive pathways for the electrons ...
maybe someone drugged me and told me all this I have no idea lol, does this theory not fit?... for example if a 3 watt cree LED consumes 3watts of power at 4.25volts, you could simply connect a 4.25v battery to the cree LED..
no resistor in sight, if i wanted 100ma to flow instead of 3watts to be consumed, i'd wire up a resistor to limit the current...
4.25/100 = 0.0425amps (0.0425*4.25 = 0.180watts)
So, let's say we use 3 resistors...
0.1watt resistor
0.5watt
5watt resistor..
now, the only resistor to get hot will be 0.1watt because there's more current going THROUGH that resistor than it can handle, even if you add a heat sink it's still going to get too hot....
now the 0.5watt is not going to get hot because it has enough pathways and enough conductivity up to 0.5watt's worth..
the difference between a 0.1watt and a 0.5watt or 5watt in all honesty?... nothing to do with heatsinking, it's not needed if the material is conductive enough....
the difference is, instead of 0.01mg of conductive material to pass the electrons, 0.01mg is used, you need to coat it with a bigger heatsink....
what you're telling me is a resistor resists, i don't see any more a case of that than any object with any kind of property that we call 'resistive' ..
now 100meters of intertwined copper wire which let's say is rated at 5amps good for small DIY jobs...
let's suppose the wire had an internal resistance of 100ohms, i have no clue actually i'm not going to look it up, and your 100 ohm resistor 50watt resistor sitting right next to the 100 meter cable, is it fair to say that in this instance both the Resistor and the huge length of wire are both doing the same thing.....
what is that exactly? both create a voltage drop, both have a resistance of 100ohms, yet how is the write 'resisting' the electrons the same way a resister does? or is it different?
on a side note, take your typical AWG chart and simply remove 1 copper intertwined strand, and allow 1 amp to flow though it, you'll get burnt so quickly if your did that, and yet with the length long enough it too could stop itself from being burnt out from a length resulting in only a hand full of ohms...
so a resistor to me is something that does not allow electrons to flow as easy as it would like (as indeed any material scaled up, including metals)... take a lead pencil scribble onto paper a nice square patch of lead, cake it on, right now with a 9v battery take the cathode and place the pin against a corner of the lead drawn scribble you just made, now take the other pen and place it against the lead, obviously you need to complete the circuit..
LED + ------[~~~~~~~~~~]------------ - LED - -Battery
basically, an LED in series with the 9 volt battery and your paper made 'resister' i don't agree with the analogy is all, a resistor no more 'resists' the flow of electrons than a piece of toast dipped in mercury...
how imagine it to work is like this...
the electrons travel at the speed of light when released from their other states of matter, eg chemically, electrochemically, photovoltaic, as the energy states move up and down, eg from photon to electron.., either way however the magnetic field is induced and captured these electrons can be manipulated to follow paths, the paths they go through are the ones with least resistance..
feel free to correct me if i'm wrong, but i'd like to show people may way of thinking regardless of how wrong i am here
however, if more electrons try to go through the semi conductor or conductor than the circuit, wire can handle, the electrons will become squeezed and no longer have any where to travel so they become heat as a side product, take 1 strand of wire and allow a few amps to flow, it will turn red hot and die and melt, you could even use a penny coin as a resistor....
So what's going on the resistor/any conductive object... well imagine fragmented pieces of metal, or metal conduits like a sewer system, now, you simply use any material that has a high resistance value, nichrome wire for example if not as a resistor it's found in electric blankets. use thicker wire and the blanket would cease to become hot....
So you say a bigger resistor has bigger heatsink, no i disagree, instead it's scaled up the impurities used in the resistor are bigger, the heat sink will still be in portion, simply larger and wider the conductor it is, more current will flow, hence when a 1million ohm resistor will quite gladly be connected to 240 volts and there would not be enough current to power an LED.
Ceramic has a high resistance value and can withstand the heat better, but you're not going to have /less/ heat it will be the same heat except Ceramic can tolerate the heat better than conventional resistors.
So a resistor /resists/ energy, it resists it no more than anything else on the planet that has some conductivity..
100ohm resistor or 100ohms of ceramic cut, you can dope anything none conductive like silicon with tiny amounts of impurities that allow it to conduct eg semiconductors and silicon.and arsenic and phosphorous... safe even on large scale.
so why use wire, why not just say wire as a resistor, oh yes, you need to roll up 300 meters to use it as a capacitor though lol, heat is only a by product if there's simply not enough conductive pathways for the electrons ...
maybe someone drugged me and told me all this I have no idea lol, does this theory not fit?... for example if a 3 watt cree LED consumes 3watts of power at 4.25volts, you could simply connect a 4.25v battery to the cree LED..
no resistor in sight, if i wanted 100ma to flow instead of 3watts to be consumed, i'd wire up a resistor to limit the current...
4.25/100 = 0.0425amps (0.0425*4.25 = 0.180watts)
So, let's say we use 3 resistors...
0.1watt resistor
0.5watt
5watt resistor..
now, the only resistor to get hot will be 0.1watt because there's more current going THROUGH that resistor than it can handle, even if you add a heat sink it's still going to get too hot....
now the 0.5watt is not going to get hot because it has enough pathways and enough conductivity up to 0.5watt's worth..
the difference between a 0.1watt and a 0.5watt or 5watt in all honesty?... nothing to do with heatsinking, it's not needed if the material is conductive enough....
the difference is, instead of 0.01mg of conductive material to pass the electrons, 0.01mg is used, you need to coat it with a bigger heatsink....
what you're telling me is a resistor resists, i don't see any more a case of that than any object with any kind of property that we call 'resistive' ..
gosh, in all that there's so many wrong assumptions etc, I'm unsure where to start lol
highly likely
no incorrect V / A doesnt = A ...... V / A = R ( resistance)
NO incorrect again, the wattage rating of the resistor isnt the initial factor causing the heating what you DIDNT state was the resistor value and the voltage and from that work out the current flowing in the circuit.
lets for simplicity say 10VDC across a 10 Ohm resistor I (Amps) = V / R 10/ 10 = 1A...
now knowing the current flow you can figure out what Wattage rating of resistor you need so that it doesnt burn up, but rather just get a tad warm and stay working
W = V x I = 10W
now say its 10V across 100 Ohms instead of 10 Ohms, what is the current flowing now ?
10 / 100 = 0.1A (100mA) = 1W
yes it has, thats why large wattage, low resistance value resistors are heatsunk
"... not needed if the material is conductive enough " ?? so you have defeated the purpose of having the resistor there in the first place. The resistor is specifically there to limit the current flow. Making it more conductive destroys that ability
pretty much irrelevent
It really is time for you to do some basic electronics study
you are not really understanding why we use resistors, concentrate on DC resistive circuits and go from there here's one good site to start at the start there are others
http://www.allaboutcircuits.com/vol_1/index.html
cheers
Dave
highly likely
no incorrect V / A doesnt = A ...... V / A = R ( resistance)
NO incorrect again, the wattage rating of the resistor isnt the initial factor causing the heating what you DIDNT state was the resistor value and the voltage and from that work out the current flowing in the circuit.
lets for simplicity say 10VDC across a 10 Ohm resistor I (Amps) = V / R 10/ 10 = 1A...
now knowing the current flow you can figure out what Wattage rating of resistor you need so that it doesnt burn up, but rather just get a tad warm and stay working
W = V x I = 10W
now say its 10V across 100 Ohms instead of 10 Ohms, what is the current flowing now ?
10 / 100 = 0.1A (100mA) = 1W
yes it has, thats why large wattage, low resistance value resistors are heatsunk
"... not needed if the material is conductive enough " ?? so you have defeated the purpose of having the resistor there in the first place. The resistor is specifically there to limit the current flow. Making it more conductive destroys that ability
pretty much irrelevent
It really is time for you to do some basic electronics study
you are not really understanding why we use resistors, concentrate on DC resistive circuits and go from there here's one good site to start at the start there are others
http://www.allaboutcircuits.com/vol_1/index.html
cheers
Dave
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Thanks for the offer, I will continue to try and guide you in the right direction
After a statement from you I am sorry but I really have to point out an old saying....
Its better to remain quiet and be thought a fool, than to open ones mouth and remove all doubt
Sorry, dont take it too personally, you just left yourself wide open for that one lol
I couldnt RESIST
But its the low resistance of that wire or penny that alows the hi current to flow and thus heat up and melt.
no the thickness isnt really relevent cause its the resistance of the wire
( will qualify that by saying for example in a pure copper or aluminium etc conductor ... thicker wire lowers the resistance
therefore for a given current flow ... say 100Amps in an overhead AC power line the Voltage drop will be lower this is good for the generating company as they are not loosing as much power in losses in the transmission line)
---------------------------------------
take 2 pieces of wire, both 10 metres long ( 33ft for the Americans amongst us)
both pieces of wire are 10AWG ... so they are BOTH the same diameter, now one wire is copper and the other wire is nichrome.
They have the same voltage connected across them
Which will get hotter and why ?
I will let you try and answer that and if you do correctly you will see why your previous statement is incorrect.
no, inpurities in the resistor wire increase its resistance and therefore decrease the current flow and therefore run cooler. LOWER value resistors across a given voltage will have a higher current flow and therefore get hotter... see my previous post using Ohms law. to recap
A 1 metre length of 10AWG copper wire may have a DC resistance of 1 Ohm
Put that across 10VDC and you are going to have 10Amps flowing. That wire is going to get REALLY hot ... its dissapating 100W ------- 10V x 10A = 100W
That 1 metre of 10AWG copper wire now has impurities in it and it 's resistance is now 100 Ohms. 10V / 100Ohms = 0.1 Amp (100mA) 10V x 0.1A = 1Watt, you will be lucky if it gets warm
Well since ceramic is an electrical insulator, we use it as an insulator. We also use it around low Ohm, hi Watt resistors as a heat disapator.
whilst thats the way semiconductors like transistors and diodes are made its NOT the way resistors are made. As I spoke of above
cheers
Dave
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Hi CJ,
A most interesting post, but you have several things wrong.
1. Nothing travels at the speed of light except light. I used to use an elecron microscope which accelerated the electrons with 100kV, they never got near the speed of light. Electrons in a solid travel very slowly indeed.
2. All resistors will increase in temperature when they pass current. Whether they get hot depends on how you measure temperature and define hot.
3. A 100R resistor and a length of wire with 100R resistance will have the same effect but the heat produced spead along a length of wire means it will not get so hot.
4. The wattage rating of a resistor depends on how well it can get rid of the heat. The bigger it is, the more heat it can disipate. Hams use small resistors immersed in a can of oil to increase the cooling and the permissible dissipation. You can get resistors mounted in aluminium tubes which can then be bolted to heat sinks, these wil have a much higher power rating.
5. Ceramics are pretty good insulators but they will get coductive when red hot. They are used in resistors as a support for the resistance wire. Nichrome is used instead of copper since it has a higher specific resistance and will stand a higher temperature.
Whether you call a resistor a resistor, restrictor or cow, makes no difference. A name is just what it is called.
Duke
A most interesting post, but you have several things wrong.
1. Nothing travels at the speed of light except light. I used to use an elecron microscope which accelerated the electrons with 100kV, they never got near the speed of light. Electrons in a solid travel very slowly indeed.
2. All resistors will increase in temperature when they pass current. Whether they get hot depends on how you measure temperature and define hot.
3. A 100R resistor and a length of wire with 100R resistance will have the same effect but the heat produced spead along a length of wire means it will not get so hot.
4. The wattage rating of a resistor depends on how well it can get rid of the heat. The bigger it is, the more heat it can disipate. Hams use small resistors immersed in a can of oil to increase the cooling and the permissible dissipation. You can get resistors mounted in aluminium tubes which can then be bolted to heat sinks, these wil have a much higher power rating.
5. Ceramics are pretty good insulators but they will get coductive when red hot. They are used in resistors as a support for the resistance wire. Nichrome is used instead of copper since it has a higher specific resistance and will stand a higher temperature.
Whether you call a resistor a resistor, restrictor or cow, makes no difference. A name is just what it is called.
Duke
its often a single solid conductor depends on what you buy, Multi stranded wire is used in places where flexibility is required)
you cant just say that a wire has a resistance of 100 Ohms. you have to define that
100 Ohms per what ? cm ? metre? kilometre ?
for discussion sake and keeping with your comments.... its 100 Ohms for 100 metres
and its coiled up beside a 100 Ohm resistor ( forget the 50W its a side issue)
Yes you have in effect two 100 Ohm resistors the reason for the physical size difference is that the cable is relatively pure copper and the 100 Ohm resistor is a short length of copper wire with impurities increasing its resistance, or carbon rod or a metal film.
Yes they will BOTH produce the same voltage drop. Its only because of the physical makeup of the resistor that allows it to be manufactured in a much more compact size
no it wont
you will find that that single 100 metre strand will still be close to 100 Ohms, probably a few Ohms higher lets say 105 Ohms. So its not going to burn out any easier than a bunch of strands.
The addition of the extra strands in the multi- strand cable lowers the overall resistance of a given length ( just the same as having a single strand of the same thickness ( diameter) of all the strands bunched together.
As commented in my last post using overhead power lines as the example....
the voltage drop is proportional to the resistance of the wire and the current flowing through it. So for a fixed current flow, changing the resistance will change the voltage drop
example 100V power supply, 100 Ohm resistor first work out the current flow
I = V / R
I = 100V / 100Ohms
I = 1A
so there is 1A of current flowing in the circuit ... out of the PSU through the resistor and back to the PSU.
so what is the Voltage drop across the 100 Ohm resistor ?
Vdrop = I x R
Vdrop = 1A x 100 Ohms
Vdrop = 100V
cheers
Dave
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Sorry, what's the difference between AWG and...? Or what's the difference between different AWG's?
Yes and no.
If they both have the same resistance, then yes, they both have the same resistance. (edit see davenn's comment -- I assumed you meant "enough length of wire to have a resistance of 100 ohms")
However, the wire and the resistor may differ in many ways.
The wire will have some inductance and distributed capacitance which will make it respond to AC signals in a way different to a small resistor (some resistors do this too). In addition it is very long and a signal will take longer to get from one end of the wire to the other compared with the resistor.
They may have different changes in resistance with temperature, age, etc. and the spool of wire may be able to withstand a higher voltage (not that it's important with a very low resistance).
If you connected them up to a LED however, you'd not notice any difference.
In terms of resistance yes, they're both providing the same function, but there are other properties as discussed above that would be different.
Well, you'd take the strand from a wire, not a table, but yeah. The total power drops off with the length of the wire (for a given voltage) and the additional length means the power per unit length is inversely proportional to the square of the length of the wire. So yeah, as you make the wire longer it gets less hot, and very quickly too.
yep, that's pretty much OK. Electrons flow less freely in the pencil marks because a thin layer of graphite is not a great conductor.
But that's exactly what happens...
You imagine wronghow imagine it to work is like this...
the electrons travel at the speed of light when released from their other states of matter, eg chemically, electrochemically, photovoltaic, as the energy states move up and down, eg from photon to electron.., either way however the magnetic field is induced and captured these electrons can be manipulated to follow paths, the paths they go through are the ones with least resistance..
feel free to correct me if i'm wrong, but i'd like to show people may way of thinking regardless of how wrong i am here
Electrons move very slowly in a conductor. In fact they have mass and therefore never travel at the speed of light.
think of metal as having a sea of electrons. As you push one in at one end, it forces one out the other end. The electrons move very slowly, but like a line of billiard balls, hit a ball on one end and one flies off the other end. The shock wave travels through the line of balls faster than the ball was moving.
No, just like the felt on a billiard table slows down the billiard balls, the structure of the conductor resists the movement of the electrons. This resistance, like friction, causes heat to be released as electrons are moved. It doesn't matter how fer or how many electrons are moving, they still generate heat. The more you try to move them the hotter it gets. This heat energy comes from the voltage across (the pressure) and the current through (the flow), and the heat generated consumes some of this available power and is seen as a voltage drop across the resistor.
In a metal, there are many weakly held electrons, it's easy to get them moving.
In a semiconductor, there are fewer free electrons and so the resistance is higher.
In an insulator, the electrons are bound tightly and it is very hard to pull them free. They have a very high resistance.
No, if you used thicker wire it would get *very hot* and probably catch fire.
The wire has a constant voltage across it and as the wire gets thicker, more current can pass through it. The power is voltage times current, so more heat.
If you want it to stay cold, use a much finer wire. It will still get warmer, but dramatically less so.
For a given voltage and length (and composition) of wire, thicker wire will cause more heat to be released.
Well it is true that a wider (thicker) conductor will heat up less for a given current, but that is simply because it has a lower resistance.
If we imagine a piece of fine wire, assume it has a resistance of 1 ohm, and can safely dissipate 1 watt. How can we make a 1 ohm resistor capable of more current?
OK, take 2 pieces of wire twice as long and put them in parallel, Now there is 4 times as much wire, so it can dissipate 4 watts but still has the same resistance. But note that as I make the wire twice as wide (2 strands) I have to make the total length twice as long to maintain the resistance.
If I wanted to make the combined piece of wire the same length, I would have to use a different wire which had a composition which gave it twice the resistance for the same physical dimensions.
So to get back to your example, there would be *more* impurities (not bigger) in a higher power resistor. But mainly the size is there to increase the surface area so that the additional heat can be dissipated without a correspondingly larger rise in temperature. As suggested in other posts, the higher power resistor may also be composed of some materials which can withstand more heat. In this case the resistor may be less larger, and get more hotter. Some resistors have fins to increase the surface area to allow more heat to be dissipated.
That's correct (ceramic can generally tolerate heat better). For a given dissipation (amount of heat) you're going to get the same amount of heat (dissipation) -- that's because they are the same thing. Ceramic resistors are not necessarily high in resistance. Construction and resistance are not that tightly coupled.
Yes (but it may have other -- often unwanted -- characteristics)
Not sure what you're saying here.
Capacitors are something else entirely. Heat is *always produced*. The amount of heat can be calculated by any combination of 2 of resistance, voltage and current. (IV, I^2R, V^2/R)
No, that wouldn't work. See my thread on driving LEDs for the reasons why.
you're talking apples and oranges here, That statement makes no sense.
that's fine as long as you remove the LED
(EDIT: I assumed that 100 was a resistance of 100 ohms -- Davenn points out that you said 100mA -- which incidentally is 0.1, not 100)if all resistors have the same resistance, then each will dissipate the same power (0.18W). All will heat up. However the 0.1W resistor will heat up much more than the 0.5W resistor, and that resistor will in turn get hotter than the 5W resistor.
No, it heats up too. But because it is larger and has a larger surface area (presumably) the heat will be radiated (and convected, and conducted) away faster.
It is possible that the 0.1W and the 0,5W resistor are exactly the same size. In this case both will get to the same temperature. The difference will be that the 0.5W resistor will have been designed to get that hot and the 0.1W will not have been.
No, presuming that both are allowed to get to the same maximum temperature, the *only* meaningful difference is how fast one can get rid of heat compared with the other.
In theory, the resistive element could be the same, with the heatsink being larger. This is exactly what we do with semiconductors to allow the same device to dissipate more heat without increasing it's temperature too much.
That's simply restating the definition. a resistor resists because it is resistive. Anything resistive is a resistor. However anything resistive is not necessarily a perfect resistor any more than anything with 4 wheels is a perfect car.
You may get confused with some of my descriptions because you have various examples assuming constant voltage, current, or power. Each of these are different and in some cases I do not think you fully understand the difference.
You really need to review ohms law and understand the relationship between voltage current and resistance, then between these and power.
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Hahahaha. The problem with long posts is that if you have your basics wrong you get yourself very badly astray.
In addition you get very long replies (which I hope you will read),
You also (as in this case) get many replies because it takes so long to prepare them that several people do so at once. I paused during my reply to have dinner, do out and get a cat, answer the phone, and reply to some late work email. It took forever.
I have tried to go back and edit my replies to explain the difference between my replies and some others. The problem is that when you get so much wrong, it is easy for different people to read the same thing different ways, or to pick different things as the starting point.
Everyone gets stuff wrong, however you're facing a rapid (re)education. Do it with grace. We've all been there. I was fortunately there in an age before the internet where my worst mistakes were not openly visible to the world
In addition you get very long replies (which I hope you will read),
You also (as in this case) get many replies because it takes so long to prepare them that several people do so at once. I paused during my reply to have dinner, do out and get a cat, answer the phone, and reply to some late work email. It took forever.
I have tried to go back and edit my replies to explain the difference between my replies and some others. The problem is that when you get so much wrong, it is easy for different people to read the same thing different ways, or to pick different things as the starting point.
Everyone gets stuff wrong, however you're facing a rapid (re)education. Do it with grace. We've all been there. I was fortunately there in an age before the internet where my worst mistakes were not openly visible to the world
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- Nov 28, 2011
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- 8,393
Excellent advice and descriptions on this thread. Especially, I like Steve's summary.
Personally I find that I don't need to think about the physics in my everyday electronics design process - when you're choosing between a 10K and a 22K pullup resistor, for example.
I think of a resistor as a way of converting a voltage into a current, or vice versa. That, plus Kirchhoff's law(s?) (and sometimes the power law and heating calculations) are enough for the general purpose stuff I design.
I agree that talk about changing its name is pointless, at least.
Personally I find that I don't need to think about the physics in my everyday electronics design process - when you're choosing between a 10K and a 22K pullup resistor, for example.
I think of a resistor as a way of converting a voltage into a current, or vice versa. That, plus Kirchhoff's law(s?) (and sometimes the power law and heating calculations) are enough for the general purpose stuff I design.
I agree that talk about changing its name is pointless, at least.
