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voltages and currents make me crazy

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shankbond

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hi, guys i m a bit confused with voltages and currents how are they related and affect any electrical device?



To start a device one needs some specific voltage say 220 volts
and current is equal to I=n*A*e*(vd)


where n is number of electrons(or density)
A is cross section of device through which it is flowing
e is charge on one electron
vd is drift velocity




now to operate a device one needs that current should flow through the windings of the motor or device

the internal impedance will affect the velocity of charge carriers (i m asking ur opinion here)

it will try to decrease the velocity of charge carriers


so, a kind of same voltage has to be applied across the conductor


but


if i see it logically ,the voltage cant remain the same through out as it appears to us , it has to overcome the internal impedance of the device so as to remain a constant drift velocity(m i right?)


how is power related to both of them ?
do devices really need constant drift velocities to run properly?




kindly help me out here people
need your help here to sort things out here in my brain?


thank you
 
You seem to have jumped to a very high level without understanding the basics. Think of electricity as water, voltage is pressure and current as the amount flowing.

It may be that you understand both of these things far more than I, if so, hopefully someone will be along shortly to answer your question.

However, I will endeavor to answer your question, "hi, guys i m a bit confused with voltages and currents how are they related and affect any electrical device?" - google ohms law.:eek:

Mike.
 
Drift velocities, current densities, etc. are usually only of interest when examining the internal operation of semiconductor devices. These parameters are not typically used when referring to current flow through normal metalic conductors.

Yes, the internal resistance will tend to decrease the drift velocity (which is simply the movement through the conductor) of the charge carriers, but the voltage applied across the conductor generates an electric field that keeps the carriers moving. The higher the resistance, the higher the voltage (and electric field) required to maintain a given velocity (current), which increases the power dissipated in the conductor.
 
I like to think of current as the water's rate of flow and the voltage as the energy in "each particle of water". I like temperature, but it doesn't work too well when you think about a resistor- pressure works better for that.
 
What you have said sounds right, but you've said it in a complicated way for someone claiming to be a beginner.
I'm also at novice levels, but will try to add some charge to your wires.
Let's say you have a battery, this has a voltage rating, e.g. 12V, this is known as the e.m.f. (electromotive force). Now that's an interesting term, elctro - has to do with electric charge, motive - driven in some way or driving something. Roughly defined.
The e.m.f. - measured in voltage - is the driving influence causing current to flow. Current flow basically is electrons moving around in some conductor.
But now the interesting part, e.m.f is not a force, but represents the energy used during the process of moving the charge or passing it on.
Does that make sense? Please don't answer that.
You can thus say that e.m.f always has something to do with energy being converted between different forms.
Now let's say you connect a resistor to your 12V battery. That charge is now flowing through the various wires as well as the resistor. But remember, e.m.f has something to do with energy being converted, so, the energy transferred to make the charge move between two points is termed the p.d. (potential difference).
That is why a voltage reading is always less after a resistor than in front of it. So if your resistor we have connected to the battery uses all the energy from the battery to pass the unit of charge we can say the p.d. across the load (resistor) is equal to the e.m.f. the two oposes each other, but is essentially the same thing, e.m.f wants to produce a charge, and p.d. wants to oppose that charge.
Does that make sense? Please don't answer.

Welcome to the complex world of electronics.
 
well that seriously adds something to the topic,



the conclusions i derive are:

the velocity of charge carriers decrease when encountering a resistance

in order to work an electric device the charge carriers need not maintain the same velocity.
 
You seem to have jumped to a very high level without understanding the basics. Think of electricity as water, voltage is pressure and current as the amount flowing.

It may be that you understand both of these things far more than I, if so, hopefully someone will be along shortly to answer your question.

However, I will endeavor to answer your question, "hi, guys i m a bit confused with voltages and currents how are they related and affect any electrical device?" - google ohms law.:eek:

Mike.


hahaha
theoretically any one who has studied electronics or electrical subjects can answer that,
but the thing is the essence of the question: what is actually happening behind the scenes?

i hope you are getting my view

peace
 
i acknowledge carl and arrie for their contributions to the article



but i still request the more senior and more experienced members to throw some light on this topic
 
The velocity charge carries lose due to ohmic resistance in a conductor is simple heating, you're definitely making this a little more complicated than it needs to be. Even in a piece of copper that isn't conducting any electricity it's free electrons are still moving at 10e6 meters per second they're just moving randomly so there is no net current flow. Try looking up thermal noise on wikipedia or google. When different electric fields appear at opposite ends of the wires the NET motion of electrons is from the positive to negative, but individual electrons don't actually move that fast from one end to another, their net motion however transfers the equivalent energy. If the current is AC the individual electrons actually don't move that far at all. With large wires and low currents individual electrons may over a very very long period of time migrate the entire length of the wire. This is actually a problem that needs to be taken into account in semi conductors as DC currents over a long period of time can cause the material to 'smear' slighty. It's called electromigration.
 
Sorry,
your original post did not mention anything about behind the scenes. Also you said that you are a beginner, that's why it's always good to start things fundamentally slowly, to wrap your brain around it properly.
But....
It seems you might be a bit more than a beginner......
I detect some false pretences in your initial post.

But you should clearly understand all about charge, and voltage-current relationship now.
Even I learnt something when going through eric gibbs's link, and remembered a lot of stuff which I've forgotten a long time ago.

I also think the point some people tried to make in that thread was that as a piece of copper wire lies on the table, it's relatively unimportant what the electrons does, until you connect it to something and send an e.m.f. through it.
Enjoy your day(s) gentleman.
 
Sorry,
your original post did not mention anything about behind the scenes. Also you said that you are a beginner, that's why it's always good to start things fundamentally slowly, to wrap your brain around it properly.
But....
It seems you might be a bit more than a beginner......
I detect some false pretences in your initial post.

i didnt get your point :(
 
For ANY purely resistive circuit, Ohms Law is all you need to know.
It is 100% accurate for calculation PROVIDED you take into account ALL resistance in the circuit including the resistance of any wires AND the internal resistance of the battery or other power supply.
All else is just wank.
 
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