V=IR R=V/I I=V/R

I don't know if this is a joke or if you miss heard. If it is in fact accurate <shudder>.

If Voltage(V) remains constant and Resistance(R) increases then Current(I) MUST decrease. It's the law, no way around it, you can try to confuse the subject by tossing in inductance, capacitance and galvanic effect plus make a very complicated series-parallel circuit but in the end Ohms Law still holds true.

Ohms Law Here is a link to wikipedia.

I hope the electricians you work with are just pulling your leg because if they are serious then they need to go back to the apprenticeship program.

Thank you very much for comment.Let 's assume we have a heating element of 500w(100v x 5ohms) of an electrical stove.Theoretically,when you increase/replace the element with a 1000w(100v x 10ohms) keeping the voltage constant ,IN THIS INSTANCE WHICH OF THESE TWO WOULD TAKE MORE CURRENT ???? If it is the 1000w then would you please explain to me a little more for me to really understand the circumstance because Mathematically, I am not able to prove this theory with Ohm's Law.

Theoretically, Ohm's Law is telling me once the heating element was increase from 500w to 1000w(obviously which is an increase in resistance) then the new current would be smaller which is practically it's not true.

OHM'S LAW IS TRUE AND CORRECT BUT I NEED SOMEBODY TO HELP ME WITH THIS TYPE OF ANALYSIS ABOVE. Probably I am missing some other compounded laws and theory.Thank you very much.

PEASE WANT TO MAKE A CORRECTION ON THE PREVIOUS REPLACE OHMS IN THE ABOVE WITH AMPS FOR CURRENT.(100V X 5A) AND (100V X 10A) THANK YOU.

Thank you very much for comment.Let 's assume we have a heating element of 500w(100v x 5A) of an electrical stove.Theoretically,when you increase/replace the element with a 1000w(100v x 10A) keeping the voltage constant ,IN THIS INSTANCE WHICH OF THESE TWO WOULD TAKE MORE CURRENT ???? If it is the 1000w then would you please explain to me a little more for me to really understand the circumstance because Mathematically, I am not able to prove this theory with Ohm's Law.

Theoretically, Ohm's Law is telling me once the heating element was increase from 500w to 1000w(obviously which is an increase in resistance) then the new current would be smaller which is practically it's not true.

OHM'S LAW IS TRUE AND CORRECT BUT I NEED SOMEBODY TO HELP ME WITH THIS TYPE OF ANALYSIS ABOVE. Probably I am missing some other compounded laws and theory.Thank you very much.

Hold everything mate! You've made a misstatement!

Theoretically, Ohm's Law is telling me once the heating element was increase from 500w to 1000w(obviously which is an increase in resistance) then the new current would be smaller which is practically it's not true.

Watts (W) and resistance are not the same! An increase in wattage doesn't imply an increase in resistance.

The problem with your example is that you left out resistance. It would be better to add it into your example for better clarity:

500W heater = 100V, 5A = 20 ohms (100V ÷ 5A = 20Ω)

1000W heater = 100V, 10A = 10 ohms (100V ÷ 10A = 10Ω)

Obviously, the 500W heater draws less current than the 1000W heater and has more resistance than the 1000W heater.

I don't know why your two electrician friends would say the opposite. They're either misleading you or you heard wrong (read my signature at the bottom).

Watts (W) and resistance are not the same! An increase in wattage doesn't imply an increase in resistance.

Very true..... check wiki for more information on the Watt.

Hooray, my faith in electricians is now restored!

Power = I*E = E^2 / R

Power (watts) = Current Squared (I^2) * Resistance (R)

Try ohms law now.

This is the form you need to remember when dealing with heating elememts!

Witch university did you graduate?

Start learning and understanding Ohm's law.

U = I*R

where

U = Voltage (you made V from it)

I = current

R = resistance

And now it makes sense.

What you called resistance is in fact the power.

When I have to engage electrical people I alway's ask them to give me Ohm's law. and explain it. It is a nice shifting method, not having to compare brown and blue eye's.

U = Voltage (you made V from it)

'E' and 'V' are commonly used to denote voltage in formulas though I must admit that I never knew that 'U' also meant voltage, I always thought it was used to denote something else.

'E' is generally used to express Electromotive force (e.m.f.).

'V' is generally used to express Volts.

'U' is generally used in Europe, particularly Germany, for Volts.

That is my understanding of the nomenclature.

John.

U is used to expressively note tension, where Volt is the unit.

It appeared that the originator doesn't really understands to formula and does not know what the letters stand for.

It is a bit like the question: I have a lamp of 60W that is broken, can I replace it with one of 20W?

Tension is free translated from "spanning", my knowledge of electricity is better than my English

Gwen

(shouldn't we start to discuss the RCD again, it has been a while since last time)

U? Here in the States it's E (electromotive force) Must be different there.

Let's blame Bush.

The E is used in electric motors, in my brain at least. (for what it is worth)

V - U - E strangely, we all know what we mean.

Guest,

I had ever the same case as yours, but my electricians were satisfied by formula P=V.I. We have 46 heaters in my factory with 15kW and 22kW at 230VAC 50Hz.

Then I challenge them to measure the resistance between 15kW and 22kW heater.

Found that 15kW = 3.2 ~ 3.5ohm, 22kW = 2.2 ~ 2.4ohm.

I said to them,"see that! which one have bigger resistance?".

So, less resistance more current more power, and at the other hand.

What theory you are missing about are P=V.I (pure resistive load) and R=ρL/A. There's nothing wrong with Ohm's Law.

Good Luck!

Heater elements (as well as tungsten etc) increase resistance with temperature.

When the element is red hot it will be drawing less current than when cold.

NOT TRUE!!!! WHO's LAW????

There are real practical devices (such as tunnel diodes AND SCRs and others), that exhibit NEGATIVE RESISTANCE characteristics!!!!!! BUT the most important thing to observe is that their ABSOLUTE RESISTANCE is not NEGATIVE! IT IS ONLY THE DYNAMIC RESISTANCE THAT IS NEGATIVE. Take a look at their characteristic curves.

Neil

IT IS ONLY THE DYNAMIC RESISTANCE THAT IS NEGATIVE. Take a look at their characteristic curves.

This is true when being measured in an energized circuit at component level but Ohm's law still proves out in the end. A simple coil is dynamic in its resistance when an AC signal is applied to it. It's been awhile since I have used the formulas so I don't recall them off the top of my head but it is a rather simple equation to determine the effective resistance as long as you have a couple knowns.

In the real world with real world applications that most of us deal with Ohms law holds true. In the box, out of the box, under the box and even on the moon it holds true.

Hi, I think someone had misguided you. When increase in resistance increases the current, you are breaking ultimate concept of ohm's law and it numerous application in the current world. The fact is When the diameter (cross sectional area) of the wire increases, the resistance decreases hence there is an increased flow in current through the wire and the Vice-Versa. Hence you could always see a thicker wire used for High voltage electrical transmission systems.

Ram

Hi Ram,

Your statement on your last sentence is not correct, because the size (diameter) of the cable/wire is not related to voltage but to the current that should be transfered through the tramsmission sistem.

You can still load a tiny wire with very high voltage and very small current. But you can't load a tiny wire with very low voltage but very high current --> it'll burn the wire.

I've put 200A @ 160 V thru a #22 ga wire. Only for a couple of ms, though! But it held it. It's a matter of heat.

Ohm's Law holds the essentials of electrical and magnetic theory. Whether it be circuit theory analysis or circuit application. It is used explicitly or implicitly in practically every electrical circuit problem.

There are electrical personals who like to mislead young electricals. I once worked with a few elecricians who tried to mislead theories and applications but failled. These situations happen espcially when thier old and your young (conflict of interest perhaps).

In my case, I was younger then them, and was thier engineering supervisor, they didn't like it, but I was incharge.

Electrical princepals/laws still holds and will not be mislead by people with conflicts of interests or joking minds.

Thankyou all for bringing to light the concept of Ohm's Law to our guest.

Long Lives Ohm's Law...Long Lives Ohm's Law...

Just a quick comment from a physicist:

Ohm's "law" is really a definition of resistance, and microscopically is represented by the formula J = sigma*E , where J is the (vector) current density (Amps/m^2), E is the applied electric field (also a vector, measured in V/m), and sigma is the (tensor) conductivity.

These may all be functions of location, temperature, pressure, etc, though typically we take them to be constant throughout the material and derive the macroscopically observable quantities I, V, R. For a wire of length L, cross-sectional area A and conductivity sigma, V = E*L, I = J*A, R = L/(sigma*A), so from the more fundamental J = sigma*E, we obtain Ohm's 'law' , V = I*R

In simple terms, applying a voltage across a conductive material creates a current that is linearly related to voltage. The constant of proportionality is simply defined as the resistance, which we can actually calculate in some simple cases.

But it gets more interesting...

This resistance may be imagined to be caused by inelastic collisions of the moving electrons with the stationary metal ions of the wire. To overcome the "friction" and keep the current flowing, the applied field must to work on the electrons and the power expended by the voltage source in doing this P =R* I^2 = V^2/R = I*V. This is the so-called Joule heating in resistive elements (like stovetop heaters), also known as "Eye-Squared-R" loss.

A typical conductor (like a copper wire or light bulb filament) will heat up as the electrons continually lose their energy from collisions. This heating causes the collisions to become more frequent and violent, so more energy is lost. This imakes it more difficult for the power source to maintain the current - the resistance has actually increased. Eventually, however, the current, voltage, resistance, and temperature all stabilize, but generally the resistance and temperature will be a little bit above their starting value.

This is very real effect and can cause problems with some halogen lamps. At room temperature they have a much lower resistance than they do at their very high operating temperatures (200-400C), so this initial ("inrush") current can be many times the operating current. Unless the power supply can deliver a short burst of this high current or the lamp is warmed up with first with a series resistor, the lamp won't start.

Stranger still, semiconductors have the opposite behavior - their resistance decreases with increasing temperature. Then we have the superconductors with no resistance at all!

This happens is true but to a certain point depending on the maximumun voltage set. Consinder this concept in AC current POWER = I²R.

FOR FIXED VOLTAGE AS YOU INCREASE RESISTANCE YOU NEED MORE CURRENT TO OVERCOME IT HENCE CURRENT WILL INCREASE WITH RESISTANCE BUT TO CERTAIN POINT WHEN FARTHER INCREASE IN RESISTANCE WILL NOT CHANGE CURRENT.

YOURS

EUSTACE MURITHI NJERU ( REPUBLIC OF KENYA)

P = I²R

Not only in AC, also in DC

Resistance is nothing to overcome, if you have a constant voltage, and the resistance will rise. The current will go down. and also the power.

Believe me, for once.

Please can you helps us with two simple samples

"two simple samples"

See my post #58 below.

I thought Kenya is in Africa and Africa is part of the planet which somehow belongs to the universe.

These laws are universal and if you discovered a new law please apply to the Nobel prize committee or publish a development from your universe. Out of Africa always something new!

The only point where these realtionships do not hold is when the element or device melts

Eustace, you are using only one formula involving power, current and resistance but you're also stating voltage which is not in your formula. To examine the problem you need to also use the other variants of the formula.

Power, current, resistance and voltage are all dependent on each other.

When you increase your resistance and your current, the voltage will increase (E=I×R).

If your voltage is constant, you use another variant of the equation:

I=E/R

So, if your resistance increases and your voltage is constant, the current will decrease.

Can you site an example with a simple potentiometer keeping the voltage constant.Believe me Ohm's law will not work.Thank.

I think it's best that you prove it for yourself.

• Get a DC power supply with a regulated output. The actual voltage depends on you.
• Get a potentiometer and connect it to your power supply (set it to maximum resistance first, else you blow the power supply's fuse, trip the breaker, or burn the pot).
• Get a DC voltmeter and connect it across the power supply's output.
• Get a DC ammeter and connect it in series with the potentiometer.

• Switch on the power and watch the voltage and current as you vary your potentiometer (be careful that you don't set the resistance too low).

You'll find that as you increase the resistance, your current will decrease but your voltage will remain the same.

I find it curious that for someone who has graduated (I'm assuming), this law has not been drilled into you. This is a fundamental and basic law and everything that you'll be doing as an electrician will hinge on this law.

This is the last post that I will make on this thread. Ohm's law and all its variants are true, it was proved to me in school and I've proved it for myself. Anyone who says otherwise is either lying or was absent when the teacher taught the subject.

From your statement Increase in resistance means increase in current which is practical and true BUT OHM'S LAW SAYS THAT IS NOT TRUE according to his formular

R=V/I this implies RESISTANCE is inversely proportional to CURRENT

Please HELP ME

RESISTANCE is inversely proportional to CURRENT.

If you have low resistance you will have high current. High resistance, low current. Always look to opposite extremes to reason things out. For example, a big fat short copper wire has very little resistance. Hook it to an adequate power source and it will quickly get red hot because it is carrying a lot of current, melting any thermoplastic insulation that might be on it.

On the other hand, a rock has a very high resistance (not a good conductor). Little or no current will flow when opposite ends of the rock are clamped between the jaws of wires coming from a power source (jumper cables is a good example).

Glad to help!

Many times the artisans use odd jargons. The electricians have done the same.

When they say "added resistance for more power", actually they must have added extra heater coil, AND this extra coil is added in parallel. Thus the total current goes up and you get extra power. Adding coil is not same as adding resistance, as coil is added in parallel.

Ohm's law will be respected all the time!!!!.

Hey Guest

The electricans are playing with you. The current will always decrease when the resistance increase.

Keep your eyes open next time, and try to check the setup :-)

Have a nice day..

Don't be fooled the more wire used i.e the bigger the cross sectional ares of the cable cores then the lower the resistance not the opposite as these fools are obviously trying to tell you.

If you look in the tool boxes of your electrician friends I bet you will find sky hooks (for holding up ladders), rubber hammers (for knocking nails in quietly) and left-handed screwdrivers (why? - you might ask)

Ohms Law is tried and trusted. Stick with it, it will get you a long way in life.

Once upon a time there was an apprentice electrician. On his first day of work he was sent to the stores with a 10/- note (remember them?) with instructions to collect a 'short circuit'. The storekeeper looked at him for a moment, eyeing him up and knowing instinctively who sent him, and said, "Wait there, son, I'll go and make one for you." Upon his return he presented the apprentice electrician with his short circuit.

On returning to the job he offered this contraption to the electrician who had sent him. What he had brought was a short off-cut of 3c PVC/SWA/PVC cable, with the conductor ends correctly prepared and lugged, the three lugs being bolted together red/yellow/blue so as to form the short circuit as originally required. Somehwat perplexed by this, the electrician nearly exploded himself when the apprentice remarked, "The storekeeper made this one for you and hopes it's correct. By the way, here's your 6d change!"

You missed the tin of electron dust

It sounds to me like those electricians have discovered an answer to the energy crisis. Heck, we can just keep adding loads and we'll never run out of power. Fantastic! Well, OK, until the generator explodes.

About your 500W heating elements, that rating is the maximum rating. The resistance of the heater coil is nominally constant (disregarding a minimal increase when heated), so when you dial in the low setting on your stove, reduced voltage is applied giving you low heat. The heat ramps on up as you twist the dial to the maximum setting. As long as your maximum setting for the heater does not exceed the rated voltage for th element at full dial, you will be getting your 500W.

I can't believe that this is even a discussion! You must be one of the electricians that our young guest is talking about. Our young guest obviously is being missinformed either by a couple of idiot electricians or for jest.

".... when you dial in the low setting on your stove, reduced voltage is applied giving you low heat."

When you dial in a low setting on your stove a reduced voltage is NOT (let me repeat NOT) applied to the element! When you dial in a low setting to your stove the full line voltage is applied to the element! What is different between the low setting and the high setting is the amount of time that the voltage is applied. On High, the voltage is applied continuously and on LOW the voltage is switched on and off repeatedly to maintain the lower temperature. Between the Low setting and the High setting, the amount of time that the element is on relative to the amount of time that the element is off is what changes (duty cycle). The temperature is related to I^t, where t is time. It is a function of the physical properties of the material as well as the electrical properties. It is the integral of the Power dissipated in the element times a constant related to the thermal conductivity of the outer sheath, the electrical insulation and the power density of the element. The temperature setting on the stove has nothing to do with Ohm's Law! (unless you consider the switch being open having infinate resistance therefore there is zero current; but that analysis is just silly.)

Remember it is better to be quiet and be thought a fool than to open your mouth (or type) and remove all doubt!!!

If you don't have a clue, please be quiet.

Of course you are correct about modern heating equipment, but consider older DC stoves that used a rheostat (remember those) in conjunction with a thermostat and relay to cycle the power. And I never inferred that time had anything to do with Ohm's Law. I have thought long and hard about how to respond to your missive and looking back at your past inputs I think you are an arrogant SOB. True, you may be knowledgeable, but the nicest thing I can think to say to you is bye bye peckerhead.

Ohm's Law: It's just not a good idea; it's the law.

You know, regardless of what you are, Engineer or electrician, you were supposed to learn this law first. Everything is pretty much based on this.

I feel dumb reading some of these posts. If some of these people are engineers, heaven help the fools

At first I thought maybe the electricians might be referring to something like an AC inductance motor, which will pull more current as the line voltage drops, to maintain power output. But no, he mentions resistance heating as an example.

To give the electricians the benefit of the doubt (probably not a good idea!), maybe they meant something like the following statement "For a constant-power load, a decrease in voltage will mean an increase in current" ? Of course, there aren't too many examples of "constant power loads"

Tom (PCB designer and technician)

Kansas

I am not sure I am fully understanding what it is you are describing. However Ohm's Law is flawless. The only thing that I could refer you to when you are speaking of "a simple string of wire" is voltage drop. When running wire over lengths you will get a voltage drop. the longer the run the bigger the drop. and as per Ohm's Law when voltage drops current rises. Longer runs in wiring create an increase in resistance simply due to the length and properties of copper wire.

When running wire over lengths you will get a voltage drop. the longer the run the bigger the drop. and as per Ohm's Law when voltage drops current rises. Longer runs in wiring create an increase in resistance simply due to the length and properties of copper wire.

I think you have confused yourself a little about what a voltage drop is. A voltage drop is the voltage measured across a resistive device within a circuit. The sum of the voltage drops must equal the applied voltage.

So lets say you have a 24VDC circuit with 10 100Ohm resistors in series. From + to - terminals you measure 24VDC, across each resistor you would measure 2.4VDC.

Actually what I was referring to was say a #10 wire run say 40' as opposed to a #10 wire run over a hundred feet. Typically you will step up to the next largest wire size i.e. #8 wire, on the longer run, to compensate for the drop in voltage at the end of the run and therefore accomodate the subsequent increase in the ampacity required to deliver the voltage down the longer run.

This can also happen in larger equipment when running #18 or #20 sometimes the length of the run can be more than 100' thus creating a voltage drop and the consequential increase in amps.

Some of the machinery I have worked on in the past have had miles of wireing in them and usually during fabrication the wire is sized larger than is required by the measurable load but is again done to accomodate voltage drop.

Any how It was just another interpretation of what our guest was asking.

Let's not slam our guest too hard!

This question is reflective of very common misunderstandings of electricity. Additionally, the misunderstandings about units are very common as well. It is not until one understands the concepts and the fundamental units that these things become clear.

I appreciate our guest asking the question rather than assuming that he/she knows the answer.

Hi:

In my opnion, the Ohm's law always works if and only if you have a constant reistence (R) and constant voltage (V) or current (I). In this way you apply V=I*R and you conclude that anytime R is constant, if you increase the voltage then you increase the current.

The problem turns diefferent if you consider a constant votage applied to a line of transimission since there you have a distributed resistence and the equations to apply are known as Telegraphist's ones.

I hope this is going to be useful for you and in case I can help you more here is my e-mail:

agarcia@uns.edu.ar

With best regards,

Eng. Andres Garcia.

No, you are wrong, Ohm's law is a Law, meaning it will always hold true. You do not have to keep the resistance or the voltage constant for the Ohm's law to work. Have you ever taken a look to the DC load line of a bipolar transistor?. You don't even have to look a the DC load line of a bipolar transistor to see Ohm's law at work when the resistance changes just look at the example that Vulcan showed (the one with the power supply and the potentiometer, every time the resistance of the potentiometer changes there is a inverse change in current, that is something that you should had learned back in basic electricity training. Please do not confuse further this poor fellow.

I am afraid he is partially correct, although he stated it poorly. The exception to Ohm's law applies to radio frequency losses which happen at high frequencies. In communications work this is a good thing, because it means that more electrical energy is turned into RF radiation. Please note the following abstract from The Journal of Applied Physics:

The Telegraphist's Equations at Ultra-High Frequencies

Ronold King , Department of Physics, Lafayette College, Easton, Pennsylvania

(Received November 1, 1934)

The telegraphist's or long line equations are derived from the Maxwell field equations for ultra-high frequencies. By taking into account retardation and the time rate of change of current, a new circuit parameter is obtained in addition to the four usually found in the conventional low frequency equations. This new parameter integrates into the radiation resistance of the parallel wires. The approximations involved are discussed, and application is made to a specific example. Physics is copyrighted by The American Institute of Physics.

At radio frequencies, RF, the "ultra-high frequencies" mentioned above (and sometimes even lower frequency AC circuits), even parallel conductors have some characteristic impedance (a resistance-like quality that is the combination of pure resistance and inductive or capacitive reactance). When conductors are at resonance (i.e. their length is some fraction or multiple of the wavelength) it becomes an antenna, receiving or transmitting electromagnetic energy, depending on what kind of circuit it is connected to. This is what make RF wireless communications and control possible.

However, this really has nothing to do with the original question, and bringing it up was just a "red herring", possibly meant to show-off his "knowledge". I agree, I don't see the connection to "variable resistance" and he only served to confuse the poor fellow. Ohm's law does hold true for all DC circuits and AC circuits which do not have significant "radiation resistance".

In fact, the RF circuit laws could even be thought of as extensions of Ohm's Law, due to the similarities between resistance and reactance and their effect on available power. While a pure resistive load converts electrical energy into heat, a purely reactive load (from inductance or capacitance) will "hide" power by shifting the phase angle between voltage and current waveforms to limit effective power. That is why industry (and even some homeowners) often install devices called "power factor correction", which are mostly just big capacitors, which counteract the inductance added to a circuit by most AC motors. Otherwise these loads must pull "KVA" and the power companies charges you more, then does its own power factor correction! They don't really charge you for "kilowatt-hours". They charge you for "kilovolt-ampere-hours". When there is no reactance, these are the same, but NOT when reactance is added.

I don't consider electricians to be the brightest, but after reading alot of these responses, I'm beginning to wonder how useful this forum is. You people are sounding like a bunch of school kids bragging about what you learned in a book. How about some actual real life thought as to why they might think the way they do. Then show how it is a more complicated formula than Ohms Law. As someone pointed out about half way through most of this garble, Ohms Law is based on the assumption that things are held constant. In real life, even passive circuits can become active. Example: In resistive welding, I have a power supply/controller connected to 2 electrodes. After I have set up the power source to the particular weld materials, if I get variations in the resistance, like air gaps, corrosion, oxidation or other types of contamination, I can get an increase in current. I would compare it to a capacitive discharge effect that can literally destroy the weld. My point is for all you responders, try adding something productive in your responses and quit wasting everyone's time on how tried and true ohms law is. I think by now everyone gets it. Think outside the box (or book as it appears here).

As a humble electrician I don't expect to be taken seriously by those outside the box, but I think you will find the increase in current that accompanies an increase 'resistance' (due to 'faults' in the weld ) still obeys Ohms Law, because there is an accompanying (but overlooked) loss of ionisation of the arc, that causes a reduction in arc resistance (by a disproportionate amount) - which (having less resistance overall) - brings about an increase in current.

I think I was trying to describe that earlier with the voltage drop occurance. I really don't think you need to be quite so abrasive. Not you horace but the other misguided gentleman above.

That being said I do have to agree with you as far as Ohms law being based on things that are held constant. However when you take into consideration we are not talking about quantum physics here just simple basic electricity then you point is quite useless.

Sorry to make a useless point, but it is a way of life for me. It is a pastime that breaks the monotony of what otherwise might have been a boring day.

But as long as we convince the 'Guest' to stick with Ohms Law; as a sound basis for making engineering decisions; it won't have been a waste of time.

Dear Sonave Sunsets ,

You said it!! Whenever we get into some vague problem, and we are not able to solve it by simple solutions my boss used to tell, "sometimes you have to stop using brains and you will get a solution to the problem." It happened many times to me as well. I was in the field for setting up PC and other hardware for a software engineer to collect data from model exchange at a training centre. I had carried whole set of tools including multimeter. We were given a table in the lab where already many PC's were connected and operators were busy with them. So we setup our PC on one of the tables and switched on. Monitor is on and PC is not switching on not even error beeps. I desperatly tried to diagnose where could be problem. We switched the power sockets, opened up the PC tried some voltage measurement and what not I tried, called the AMC holder asking him for instructions or requesting him to replace the motherboard etc. Finally my boss, sitting 2000km away (Bangalore India)from the field setup asked us to visit our other office just 50km away (New Delhi India) and said he has arranged a new PC for us to pick up and set it up. We took faulty(?) PC to the office and as didn't have time to analyse the problem, we just got a new PC came to the field and tried powering up. Alas! The problem repeated. For moment I thought my brain will explode with the tension. I calmed myself and thought for a while and in a sudden flash the idea appeared in mind to check the supply voltage. Alas! it was 110VAC. AHHHHHHHH! that was the problem. Why I didn't think of this, because the other PC's were up and running and our monitor was powered up. The other trouble was that the Lab incharge was watching us all the while but did not hint us about the voltage he very much knew that the Japanese equipment along with the PC's were working on 110VAC. By now we got a call from our office that whichever PC we had carried to the office was perfectly ok. When my boss came to know about this he said that "sometimes you have to stop using brains and you will get a solution to the problem.", for the first time to me. Though I am not apply this always, many times I remember this and have applied simple solutions to what looked like complex problems.

I hope I have not bored you people.

So not only do you not understand basic electronics but are unable to perform basic electrical troubleshooting. I would applaud your courage in your willingness to tell us about your shortcomings if it was not done in agreement with another person with obvious shortcomings.

Try re-reading some of the original replies, you will notice that the simple "No Brainer" answers were given by several people.

This is sad, very sad.

I suggest that people should look at the literature first. Simple and simple. Ohms law is consistent, it works, has worked, and will continue to work for the practical world. However, in the nano world, > 500 nm ohms law runs into a physics wall. That wall being contact resistance, polaron formation, and work function barriers, and this is just the start for a simple measurement. But for all other applications, ohms law works to the second order function.

Now lets move off the silly and move to a something good, like hole injection, tunneling, HOMO and LUMO for organic conductive materials.

I can not think of anything else but a practical joke, unless your electricians were talking about parallel circuit

V=IR

P=VI

1000W @ 10A - V= 100V, R=10 ohm

500W @ 5A - V=100V, R=20 ohm

Pineapple

Ok, lets put this one to bed with a nice cup of Milo (or hot chocolate), personally I prefer a nice cup of tea . Anyway, from the information provided by the original poster (the original post and the followup #3 and #4) it is quite clear that the guest has misinterpreted the ohms law formulas.

V=IR, P=VI, and P=IV²R. Enough said, oh except for this (directed at everyone on CR4). Please, Please, Please read the original poster's questions and followup replies carefully. I cannot tell you how many people on this site will go of and answer a question that wasn't asked or, miss the point of the original question entirely.

Anyway I digress, now in response to the requested information on setting permissions within Vista when running a quad-core Intel processor with a system memory of only 500MB.........

Quote > "P=IV²R."

WTF??

misprint, right?

yes.

The current? The resistance? Huh,I am pretty sure there are two off-duty electrician out there doing upstream kayaking...

OMG!

This just goes to show you the sad state of industrial technology in the Third World. Perhaps instead of sending all their bright young university students to Western universities and colleges, they should consider sending their top scoring apprenticeship applicants to our trade schools, or else recruiting some of our Vo-Tech and trade school teachers to staff their schools.

I wonder how many Indonesians died of accidental electrocution so we can enjoy our Walkmans, I-pods, and HDTV's here in New Zaustralnorthameropa and Japan?

Tongue is firmly planted in cheek of course.

And to the fellow that inferred that sky-hooks, rubber hammers, and left-handed screwdrivers do not exist...guess again!

Sky-hook: What dangles on a cable below a load lifting helicopter.

Rubber Hammer: Used to safely nudge all manner of delicate, but motion resistant items. Especially useful for woodworking, plumbing with PVC, and knocking plastic or aluminum tent pegs into the ground!

Left-handed screwdriver: Shift a right-handed screwdriver to your left hand. Now it is left-handed!

I especially enjoyed the story about buying a Short Circuit!

In Boy Scouts we used to send the newest Tenderfoot over to the next Troop to borrow their Smoke Shifter (for campfires) or their Tent Stretcher (back when most Scouts used canvas wall tents).

In the US Air Force many young Airmen fresh out of training were sent to fetch striped paint, elbow grease, prop wash, or 100 yards of Flight Line. I guess these days they might be sent to get a Jet Stream or a Radar Range.

Oh, well. Off to the Hunt. Now where did I leave my Snipe Bag? Ah, yes. I loaned it to the fellow out in the woods the other day who was left holding it while I and the other Beaters began driving the Snipe towards him.

ROFLMAO

It was a 'leg pull' ...And to the fellow that inferred that sky-hooks, rubber hammers, and left-handed screwdrivers do not exist...guess again! .. as you say they do exist, but in the context of the original question these were the things that (as apprentices) we were sent on as fools errand - much to the fun of everyone else.

I know only too well about the rubber hammer - it was one of the first I was caught on. I did not believe it for the moment - but back in the 50's you did as you were told - and I was sent to the stores to get one (the Store-man was in on it) and quite explicitly I was told by the foreman not to return to site without one, even if it meant going around the builders merchants to buy one. Obviously the stores' did not have one, so of I went to the tool shops, but to no avail. I popped into Woolworth's and quite by chance I found a rubber hammer on the baby's toy counter - 7¼d it was (an hour's wages for me).

Anyway to cut a long story short, I went back to site - but not before spending an hour or so in the local News Theatre (no TV then). Where the bl**dy h**l have you been all the afternoon!...

I kept that one quiet, other than to say I had trouble finding a shop that sold them (lots of laughter). The sequel to that was when I asked the foreman for my 7¼d back which he paid - but the joke was still on me.

To be honest, although I was convinced it was a leg-pull, there was a little nagging doubt in my mind that (perhaps remotely) rubber hammers (not the toy ones) were real.

And this is the point here, we all believe in Ohms Law. But, and it is a big but, is it possible there might be some truth in the original concept - and if true - wouldn't we all like to know.

Electricians typically aren't that up on the mathematics of electricity unless they're into some pretty sophisticated commercial stuff. The formula holds true. If you change the value of any of the variables, then the value of one or both of the other two must change to maintain the equality.

Ohms Law throws up some interesting questions when you change the variables.

A 240 volt circuit with a 20 ohm resistance, when switched on, will pass 12 amps in steady state conditions.

Now switch it off. The resistance is now infinite (nigh on) - but at that instant when the current was 12 amps - what was the voltage - at that instant (240 or I x R ?).

Interesting what.

Theoretically the current drops to zero as soon as the switch is turned off, or the resistance turns infinite, while the voltage across still and always remains 240.

But in reality the current can not be turned off to zero immediately. Instead, it will keep flowing for a very short or almost invisible period. But it doesn't mean anyting against Ohms Law. Once the two contacts of the switch take apart, the voltage will apply to the air (or any other insulation media in-between) gap, which results in spark which bridges the residue current. As the contacts leave each other further, the gap becomes wider and wider, the spark gets thinner or the resistance getting bigger, causing the current dropping lower (see, Ohm Law!) untill the voltage is not enough to maintain the spartk. That's the time for the current hits its ground zero at last.

All above happen in a very short period...too short for my eyes to catch...I am near-sighted, by the way.

Voltage, type of insulation, the resistance in series, or even ambient temperature play their rols in the way the current drop. All are matter of drop gradient of current.

Thanks for that. There also could be inductive and capacitive energy to dissipate - so there might be a rise of voltage - such as in an ignition coil due to the rapid loss of current. Similarly in power switching of grid lines, the voltage across the contacts of an open circuit breaker could increase enough to re-strike the arc.

What a load of twaddle has been talked about on here.

Sounds more like school kids arguing in the playground than experienced engineers.

This is yet another discussion being deleted from my watch list...

I think it's entertaining..

(yes I'm having a dull day)

In order to solve this problem and get to the truth in it, you MUST think like an electrician and not like an electronic designer. Electricians think in terms of LOADS. If someone buys a toaster and plugs it into an existing home service, he has added a load (resistive or not, it's a load). When a load is added to the circuit, more current is reqired to power it (at a constant voltage) so the electrician says the current increases because the load(resistance) increases. He can prove it too because he says that as you add more loads you get to the point where it pops the circuit breaker and that wouldn't happen if the added resistance( his load) didn't increase the current. Therefore, in the mind of an electrician, increasing resistance increases the current. What he is really saying is that the current DEMAND increases at a constant voltage. The LOAD he refers to is actually power and not pure resistance.

Are you saying that electricians do not know the difference between LOAD (power consumed), which is Voltage multiplied by Current, and RESISTANCE, which is Voltage divided by Current?

That would be one very sorry dumb SOB! I have never met a qualified electrician who was that stupid!

To avoid any further confusion, delete the last sentence in my post #66. How would you respond to the line of thinking of the electrician in my post?

Your last sentence notwithstanding, a qualified , competent electrician would NEVER confuse a LOAD (measured in watts or Horsepower) with RESISTANCE (measured in Ohms). I could understand some confusion between Impedance and pure Resistance, since they are both measured in Ohms, but not LOAD!

If I was working with an electrician who was espousing the line of thinking you describe, I would first check to see if he was pulling my leg (as many are known to do with Engineers), then politely explain the difference. If he continued in his erroneous thinking I would find a electrical circuits text, photocopy the appropriate pages, and highlight the most significant text before handing it to him.

maxmutant,

I had said that I wasn't going to contribute to this thread anymore (though I kept it in my subscribed threads). I was getting a bit distressed at all the misconceptions I was reading. This time I just had to come back and say something.

Load and resistance are not the same. Electricians need to get that into their heads. Your concept about load being equal to resistance doesn't apply to electricity.

You seem to be equating this to an example like a wagon that is being pushed. Adding load to the wagon increases its resistance (it's harder to push). Remember, however, that the term "load" here refers to the weight (which determines the resistance of the wagon to pushing). It is not the same as power (which electricians refer to as "load"). So what's it going to be? Are you going to think like an electrician or as a non-electrician.

I believe that in order to understand what the electrician meant when he told his assistant(the originator of this forum) that "increase in resistance, increased the current", I will have to think like THAT electrician. Here is an example of how I believe THAT electrician was thinking:

Add an electric space heater to a room. The heater is rated at 1100 watts at 110volts. Therefore it draws 10 amps current. The heating coil is 11 ohms. By adding the heater to the existing circuit you are increasing the resistance in the circuit and increasing the current in the circuit. Therefore, the electrician turns to his assistant and says, " you see, increase the resistance, increase the current"

Now, I'm not saying that I think that way and I know ohm's and Kirchhoff's laws inside and out. I'm trying to solve the mystery that was presented to all of us and the solution has not been as simple as telling the guy that he doesn't know what he's talking about. There are semantics involved here which are being overlooked and that's why I said in my post #66 that it is necessary to think like an electrician whether or not his terminology is technically (electrically) correct.

I would like to suggest that the originator of this forum print out this post, take it to the electrician and ask him if that was his line of thinking when he said increase resistance, increase current. Knowing that would solve everything. I hope he reports back.

By adding the heater to the existing circuit you are increasing the resistance in the circuit

Ah! But any electrician worth his salt knows that when they add a load to a house circuit, they are putting it in parallel with everything else. Connecting resistances in parallel actually reduces the total resistance, thereby increasing the current and the power consumption. Therefore, Ohm's law still rules.

I already understand what those two electricians mentioned in the original post thought or at least what our original poster thought they said. The fact remains that the concept that current increases with an increase in resistance is incorrect.

Let's put this thread to rest PLEASE!

Mr. Vulcan,

I believe the human electricians in question were either being deceitful in a vain attempt at "pulling his arm", as the humans would say, or they were being completely illogical. I would put the odds at 66.6666% in favor of the former and 33.3333% in favor of the latter, with a .0001% chance they were under some form of mind control by an evil alien creature.

Live Long and Prosper!

either being deceitful...or they were being completely illogical

It's difficult to determine which of which they were trying to be. I could probably find out by using the Vulcan mind meld but we haven't worked out a way to do it via the Internet.

Still in all, this thread seems to have opened up a bad case of inadequate training in some schools or colleges. I've had the fortune of having good teachers but even then, I've had classmates (who had the same teachers) still get it wrong! Just an another example of the IDIC:

Infinite Diversity in Infinite Combinations

It makes life so challenging/frustrating/interesting/sad/funny...

I've re-read the first few posts by the "guest" and nowhere do I see any mention of college or any other formal institution of learning. I believe he's just an apprentice working with electricians who may have an interest in electricity and knows how to use the words -"theoretically, mathematically and compounded laws"

By the way.. where is our guest? He could at least thanked us for trying to explain Ohms Law to him (or her)

"Add an electric space heater to a room. The heater is rated at 1100 watts at 110volts. Therefore it draws 10 amps current. The heating coil is 11 ohms. By adding the heater to the existing circuit you are increasing the resistance in the circuit and increasing the current in the circuit. Therefore, the electrician turns to his assistant and says, " you see, increase the resistance, increase the current"

Max, by your way of thinking you could just as easily have said, "The heater is rated at 1100 watts at 11 ohms. Therefore it draws 10 amps. The heating coil voltage is 110 volts. By adding the heater to the existing circuit you are increasing the resistance in the circuit and increasing the voltage required in the circuit. Therefore, the electrician turns to his assistant and says, " you see, increase the resistance, increase the voltage. Better put in a transformer to bring the voltage up to 220!"

Is that not a ridiculous statement?

The 1st post read:

"increase in resistance increased the curent" -could mean increasing the physical number of heater elements in the building or room or oven or..., not properly explaining Ohms Law, but a simple numerical concept to try to convey not electrical formulas, but a situation to help a beginner understand, not realizing that he would try to apply Ohm's Law to it. Or.. (as mentioned before)--they were pulling his leg.

Steve-O,

That is the same argument that "maxmutant" tried to sell in his post#66, but I (for one) am not buying it. Electricians know what "resistance" means, and they don't confuse it with "loads", "physical number of heating elements", or whatever. If they do, then they are not much of an electrician in my book.

Electricians (and others) use a simple mnemonic device to remember Ohm's Law, and don't need to memorize any complelx electrical formulas:

I still believe they were either pulling his leg, or just plain ignorant. Although, there is still that outside chance their minds are being controlled by evil space aliens!

I like the space alien theory.

Actually, judging by the spelling (or lack thereof) in the guest's posts, he's on the other side of the earth and sometimes things do not translate from there to here very well. (my theory)

Hello Guest,

I also was also blinded all these days about the increase in resistance-increase in current concept. All while I was applying I=V/R and everybody else in forum were talking mostly about that same formula. The electrician is just trying fool you and don't get carried away by him. You just apply the following formula:

1/R = 1/R1+1/R2+...1/Rn

See it yourself. With addition of resistances the overall resistance decreases and thereby increasing the current simple. When your electrician says he has increased he is hiding the information that he is actually adding the resistance parallely and not serially which has the formula:

R=R1+R2........Rn

R. GANAPATHI RAO,

C-DOT

INDIA.

Yes I agree. It is a play on words.

I built a little 12 volt circuit board initially using 5 resistors. When measured, the current was 2 amps.

I really wanted 3 amps - so I added more resistors until I got it.

But yes, as you say, they had to be added in parallel.

I agree. "Adding" more resistance -( in parallel)- equals more I.

Please, let's not encourage this wrong-headed thinking. When you place resistors in parallel, you may be adding "resistORS" but you are NOT adding "resistANCE" to the circuit.

If anyone says that current will INCREASE when adding "resistance", ask them what happens when you add that "resistance" in series and not in parallel. If they say that current will then decrease, ask them how it is possible that adding the same characteristic to a circuit can have the opposite effect. Then politely point out that they are NOT adding "resistance" but adding "resistors" to the circuit and that adding resistors in parallel causes overall resistance to DECREASE, because you are increasing the number of paths that the current can flow in while the average resistance in each path remains pretty much the same and that is why current will increase. However, if you put all of your resistors in-line (series), you are not increasing the number of paths, but you are increasing the resistance of the one path, so current must decrease with this increasing resistance.

I think that we're just trying to figure out what the original poster was trying to say.

Agreed, it's incorrect, backward and nonsensical.

we have no idea what any of this information in the fromula V=IR. whats should we do?

As this is Ohm's Law.

As it concerns Electricity

There is only one advice for the future: Keep your hands off.

Sorry if it seams rude, but electricity is dangerous and you only feel it when it is to late. If you don't have a clue about Ohm's Law you should take back your school books of the first grade, somewhere in the physics the answer must be hidden.