Voltage v/s current........!

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Girishh

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Hey guyss....


, please give your view...If voltage decreases current will increase or decrease.. ..??.:!:
 

As per Ohms law Voltage is directly proportinal to current. So with resistance remaining constant, if voltage decreases current will decrease and if voltage increases, current increases too.
 

It depends on the third parameter by which voltage and current are related - resistance. According to Ohm's Law, V = IR. So, if R is constant, V is proportional to I: current increases as voltage increases and vice versa.

If you have a resistance that is variable - changes depending on voltage and current conditions, you need to consider that. Despite that, however, in general, you should find that current increases with increasing voltage, even though they don't have to be directly proportional (eg incandescent bulbs).

Hope this helps.
Tahmid.
 

LvW (EDIT: and Tahmid) is right. Starting from Ohm's law, V=R*I, let's go through the maths:
V=R*I -> Let's assume R is constant, for instance: R=5. Then we will have:
V=5*I;
If current changes, what happens?
I=10A: V=5*10=50V;
I=100A: V=5*100=500V;
I=0.1A: V= 5*0.1=0.5V
If voltage changes, what happens?
We need to use the inverse formulas to get the current value based on voltage, so:
I = V/R -> Still assuming R is constant, R=5. Then we will have:
V=300V: I=300/5=60A
V=15V: I=15/5=3A
V=0.125V: I=0.125/5=0.025A

As you can see, considered a constant R value, Voltage and Current are directly proportional one to each other.
@yassin: The power is not constant! The power is dependent on the voltage and the current, as of W=V*I. Considered that V=R*I, you can also write W=R*I*I. In this last expression, considered a constant R=k value, the amount of current will determine the voltage (as of V=R*I) and consequently the amount of power. Changing the voltage value, considered the same R=k constant, means that I has changed too. If I it's kept constant, the voltage will not change; and if V is kept constant, I won't change.
 
Last edited:

LvW said:
Yassin, my suggestion is to answer only in case you are pretty sure that the answer is correct.
Did you ever hear about ohms law?
Click to expand...
Yes i know ohm law, it's basic law i learnt when i was in school, but me i am talking about power conservation, for example in a transformer the input power will be the same as output power, so P=Uin*Iin=Uout*Uout,
 

@yassin.kraouch, I understand why you have put this, the original question is vague and incomplete. The vast majority of people here would interpret the question to be about conduction though, whether through an ohmic conductor or not. Things get lost in translation I suppose.

@Girishh, See if this helps you understand what is happening:

'Voltage' is an improper term for potential difference (which is measured in volts). Everyone uses the term, but we should remember what it really means.

Potential difference between two points gives rise to an electric field between the points, and an electromotive force on anything charged within that field.

In a metallic conductor, there are free electrons that can move (slowly, termed 'drift') within the metal. These are negatively charged. So, when put under the influence of an electromotive force, the electrons drift towards the positive end and away from the negative end.

The rate of this drift of electrons is called current.

You can imagine how increasing the strength of the electromotive force will make the flow of electrons increase, just like increasing water pressure in a pipe causes more water current.

So, increasing the 'voltage' will cause an increase in the current that flows.

Never forget that it is always the electromotive force, which arises from the potential difference (voltage), that causes current to flow. Even in so-called current-controlled devices like bipolar transistors, it is still 'voltage' that causes everything to happen.
 

Hi FoxyRick,

I cannot agree with all of your comments.


So - what is your explanation for the term "voltage"? To me, it is just another name for an electric potential difference.


In this case - because the drift velocity is relatively slow - also the "current velocity" would be much smaller than can be observed in reality.
In contrary- the following definition applies: Current=Movement of charges (NOT of electrons).
That means: The phenomenon we call "current" is just an effect we can observe - but without the necessity for movements of parts (particles, electrons).

Regards
LvW
 

To me, 'voltage' is a term that has entered common use but does not convey as much meaning as the original term, potential difference. Historically, potential difference was the term and it was measured in volts. Thus, the word voltage eventually became a slang term for PD.

Yes, those of us with more than a certain level of knowledge know what it means and perhaps my point is trivial. When teaching though, I found that insisting on the use of the proper term, PD, tended to speed up the understanding of what was happening. Using a term that describes the phenomenon rather than a slang term is better.

I agree that current = movement of charges. That is a more general explanation that can be applied in more instances than current = movement of electrons. I was talking about a metallic conductor though.

I disagree that there is no necessity of movement of particles. Charges are bound to particles. Particles carry the charge that is actually moving, whether it be an electron, ion, positron, etc.
 

Agreed, sort of. I'm comfortable with the term "voltage", but don't like it when I see "amperage" and "wattage" instead of "current" and "power". Maybe that's a bit hypocritical, though. I can imagine that 50 Yrs ago serious folks got equally annoyed when the sloppy youth of the day started using the term "voltage".

Times are changing though. With the advent of texting a lot of people seem to have lost all interest in spelling, punctuation, grammar and capitalization. Another 10 years and the next generation will be grumbling that "wattage" is the correct term, not "wtatge LOL"
 

Not disagreeing with the replies...

Here is an example of a case where increasing the current will decrease the volt level...

example, when increasing current draw from a power source.

The direction of cause and effect is different in such a case, naturally.
 
Thanks for your views...Actuallyy acc to ohms law ...u r correct ...but if we consider the case of power like Power=V.I than if voltage decrease than to make power constant current has to increase....please comment
 

Girishh said:
Thanks for your views...Actuallyy acc to ohms law ...u r correct ...but if we consider the case of power like Power=V.I than if voltage decrease than to make power constant current has to increase....please comment
Click to expand...

If you do somehow have power constant then yes, if voltage increases, current decreases and vice versa. An example I can think of is if you have 2 200W DC-AC inverters (with 12V input, running from batteries), one with 110V out and the other with 220V out, then, at maximum load (which is 200W), the current will be half at the output of the 220V inverter than for the 110V inverter.

But, be careful regarding this, as the two loads will be different in this case and you have changed the resistance to keep power constant.

Another simple example would be just a transformer. Imagine a 220V to 22V transformer. The power in equals power out (power is constant). So, current through 22V winding is 10 times larger than the current through the 220V winding.

Hope this helps.
Tahmid.
 
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