jrannis
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Ok lets go back and look at the 240 volt water heater operating on 120 volts.memyselfandI said:Can you increase voltage and current simultaneously?
Ok lets go back and look at the 240 volt water heater operating on 120 volts.memyselfandI said:Can you increase voltage and current simultaneously?
In most real applications however, as the current increases the voltage will decrease. The reason the current increases is due to a reduction in resistance and (so long as the source and keep up) an increase in current flow will be, for the most part, proportional to the increase in Watts produced.
Although it is rare, it is possible to increase voltage and current simultaneously. It probably is rare because without a corresponding change in resistance, such a simultaneous increase would cause damage to the system.
memyselfandI said:Can you increase voltage and current simultaneously?
Yes, but is the current instantaneous?chaterpilar said:Coming back to OP, another misconception people have is that "voltage" kills....it is actually "current" which kills...and high voltage just has higher potential to drive the current through the body.
LarryFine said:Yes, but is the current instantaneous?![]()
The first time I read this, I did not follow. I read it again and still don't follow. The best I can tell is maybe you are trying blending in the idea of economic line design, where some of the contributing factors are voltage drop and line loss.K8MHZ said:All Ohm's Law states is a relationship between (at the basic level) volts, amps and Ohms.
*Any* of them can go up or down in any manner, simultaneous or not, and the equation still holds. The manner is dictated by the system or the device and is only explained by the Law.
In most real applications however, as the current increases the voltage will decrease. The reason the current increases is due to a reduction in resistance and (so long as the source and keep up) an increase in current flow will be, for the most part, proportional to the increase in Watts produced.
Although it is rare, it is possible to increase voltage and current simultaneously. It probably is rare because without a corresponding change in resistance, such a simultaneous increase would cause damage to the system.
We like it when the volts go up and the amps go down. Conductors are sized in amps and the smaller the conductor, the less money needed to buy them.
True. As we all know, relationship for instaneous V and I values for reactive loads are:rattus said:...We can extend Ohm's law to impedances, but in that case V and I must be RMS values, ...
Again, as we all know: Really hasn't got any thing to do with E leading I, or E happening before I - or which causes the other. Just has to do with with what happens when a function (waveform) is differentiated. ELI the ICEman works only with sine waveforms.rattus said:... and for practical purposes changes in V and I occur simultaneously.
gar said:080621-1833 EST
rattus:
Your quote is incomplete and I have no idea what the intent of the statement is without the complete discussion.
If I have a dissipating device (meaning power, and no energy storage) then r = v/i makes good sense even if resistance is not constant.
A 100 W incandescent lamp with 120 V excitation has a resistance of 144 ohms and a current of 0.83 A at that operating point, and also has a small signal resistance of 144 ohms at that point. Does it make sense to describe the resistance under these conditions?
This same lamp has a resistance of 9.6 ohms at very low current. Fluke 27 measurement. Does it make sense to define the resistance at this point?
Subject this lamp to some infrared excitation, a heat lamp, and the low current resistance measurement is 12.5 ohms. Again does it make sense to define resistance at this point?
Are you saying that we can not define resistance as v/i under these different conditions for the same device?
The resistance of the lamp when cold will define the initial inrush current from a DC source, and the steady-state resistance when 120 V is applied will define the power consumed over a long term average and thus your electric bill. Certainly I would not use 9.6 ohms at 120 V to determine power consumption as it relates to my electric bill. However, it is true that the instantaneous power at turn-on with 120 V DC is 14400/9.6 = 1500 watts.
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ELA said:Rattus,
Nice quote from 1954I am almost that old!
As a strict definition, many definitions for ohms law can be found , even today, that state the choice of R as the constant of proportionality.
Would you agree that like many math equations you can also choose another quantity to be the "given" or as some might call, the constant, and then calculate to determine the "unknown" quantity?
I myself have used ohms law often to calculate voltage or current in circuits with variable resistances? Or used a constant current source and a variable resistance to generate a varying voltage.
There are resistances that are not independent of current , of course these are non linear. While ohms law is generally described as being used in a linear circuit, or the linear portion of the curve, does it not still apply at any given instant along the E or I curve of a non linear resistance device?