It matters when people don't truly understand whats going on!

I have seen it FAR to many times where people think that you can make current (i.e. supply current which produces a voltage).

and what is wrong with that? ever used current source?

thinking that current is result of voltage can also be misleading....

so what is equation for calculating voltage drop? V=IR
and if you do anything analog (either power or opamps) voltage drop is everywhere.

where is voltage source when you have emission of ions? (radiation)

how do you explain chemical batteries?

how do you explain boost converters (SMPS), eddy current and more?

 

Point taken.

What Robin Mitchell is implying is that when you have a formula

y = f(x)

y is the dependent variable.
x is the independent variable.

Ohm's Law states that current I is directly proportional to the applied voltage V and inversely proportional to the resistance R.
Hence Ohm's Law stated algebraically is

I = V / R

I is the dependent variable.
V is the independent variable.

V = I x R and R = V / I are corollaries of Ohm's Law.

It is best to use I = V / R when trying to explain Ohm's Law to someone new to the subject.
Of course, if you are doing circuit analysis and I and R are both known then one can apply V = I x R.

 

@panic mode You raise a good point about ion flow (I would have to think on that one) but your other examples are wrong. A "current source" is a voltage device that adjusts its voltage until the desired current is met. Boost converters are a result of capacities coupling / induction fields collapsing which all involve electric fields (voltages). Eddy currents are a result of an induced EMF (voltage).

 

http://www.qrg.northwestern.edu/projects/vss/docs/power/2-how-do-batteries-work.html

This website explains chemical batteries well. The only reason why the electrons want to move around is due to their charge which results in a potential difference.....which results in current flow!!!!

 

As you say, Robin Mitchell, starting from voltage to explain things is probably a good idea. But your assertion the the "formula is wrong" is quite incorrect. It probably would have helped to rephrase your original post along different lines.

 

As you say, Robin Mitchell, starting from voltage to explain things is probably a good idea. But your assertion the the "formula is wrong" is quite incorrect. It probably would have helped to rephrase your original post along different lines.

I can see what you mean that to say the formula is wrong, is wrong. What I mean is that the formula V=IR should be written as I = V/R

 

don't get me wrong, i personally also like to think that (in most cases) current is a result of voltage. i am merely opposed to prescribing ... to others ... how to look at the world, particularly things that are not directly observable with human senses. algebraic equation presented in one for or another is more accurate than another when BOTH forms are used million times a day every day? because that is easier ... for others...? i would not hold my breath.

 

If you believe the left side of an equation causes the right side of the equation.......then everything can cause everything.
You can put anything you want on the left side. An equation only shows the mathematical relationship of the measurements....not the cause. It's an equality table of results. You may look at the equality from any side.

Does I = V/R explain why or how R limits the I? Even if R goes to zero.....I would be limited. There are only a certain number of charge carriers, in any media.

In a lightening strike the R is very low. The current is heavy, but not long lived. It runs out of charge(current).

 

What I mean is that the formula V=IR should be written as I = V/R

It all depends on what you are wanting to find. The unknown is on the left of the equation so you transpose the equation to suit the purpose of resolving this.
I'm really having trouble following your logic. R=V/I is just as valid as V=IR and I=V/R.
They are all the "same".

I use them all at one time or another. If all I had was "I=V/R" and could not transpose them to find the unknown, life would be a lit harder.
By the way, I use "I=E/R" anyway

 

Actually the correct way to express ohm’s law is…

“E” over I times R…not “V”

Spidey runs for door>>>>>

And JFTR, in most common circuits where the voltage is not from the primary or a secondary source, voltage is “developed” across a resistance when current is run thru it.

Ok, I’m really leaving this time…

 

Ok, I’m really leaving this time…

I think I will too. this has been done to death, and the original question from the TS lost along the way.

 

http://www.qrg.northwestern.edu/projects/vss/docs/power/2-how-do-batteries-work.html

This website explains chemical batteries well. The only reason why the electrons want to move around is due to their charge which results in a potential difference.....which results in current flow!!!!

But where does the potential difference come from? From a chemically-induced charge separation. But, by definition, the act of separating charge is a current. Those charges do NOT separate because of a potential difference -- they are going the wrong way for that! Work is being done on them by the chemical reaction which is what is resulting in the potential difference. So the chemically induced current results in the cell's potential difference.

Many examples could be constructed in which a current produces a voltage. Your every day static electricity is an example. The barrier potential across a pn junction. The inductive kickback voltage of a coil. The sensing current in an ionization smoke detector.

In fact, fundamentally, the only way to produce a potential difference is to create a charge separation and, once again, separating charge is, by definition, a current.

 

Currents dont magically move by themselves

 

In a battery, there is an ion buildup during the chemical reaction. However, this is due to a "electro potential difference" where ions move. These ions move due to an electric field from other chemicals / ions which is a voltage field (i.e no current flow without a potential difference)!

 

Currents dont magically move by themselves

Sure they do. What voltage is driving the current in a superconducting magnet?

But that's beside the point. I already stated that the current resulting in the charge separation that results in a voltage is the result of work being done on the system. Chemical work in the case of a battery, mechanical work in the case of static electricity.

 

In a battery, there is an ion buildup during the chemical reaction. However, this is due to a "electro potential difference" where ions move. These ions move due to an electric field from other chemicals / ions which is a voltage field (i.e no current flow without a potential difference)!

How does this electric field exist without a charge separation?

 

"Voltage or the current?". Dilemma...
It is all about energy. Electrical energy forms are either potential (shows as voltage) or kinetic (shows as current).
We can store electrical energy in:
1. Capacitor (potential form, separated charge carriers, voltage. Current is zero).
2. Superconducting coil (kinetic form, moving charge carriers, current. Voltage is zero.).
Resistor is very effective (efficiency factor = 100%) converter of electrical energy to electromagnetic waves (we feel them as heat, light).
If resistor is connected in parallel to capacitor, voltage creates current through resistor.
If resistor is connected in series with winds of superconducting coil, current creates voltage on resistor.
Relation between voltage and current is constant for a particular resistor (resistance=V/I, conductance=I/V).

 

In the superconductor, current flow was initiated via external magnetic fields which is essentially an electric field being applied on the electrons. i.e. charges only move once a force is applied on them. i.e. no current flow without a voltage field or some external force.

 

"Voltage or the current?". Dilemma...
It is all about energy. Electrical energy forms are either potential (shows as voltage) or kinetic (shows as current).
We can store electrical energy in:
1. Capacitor (potential form, separated charge carriers, voltage. Current is zero).
2. Superconducting coil (kinetic form, moving charge carriers, current. Voltage is zero.).

The problem with this is that current (as the energy carrier) in circuits usually carries very little kinetic energy because when it does have high kinetic energy that energy is usually converted to heat or radiation because of accelerations. Superconducting coils and Capacitors both store electromagnetic potential energy that can be expressed as an electric (charge separation) and/or magnetic (charge movement) fields in combinations.

The physics meaning of electricity is a 'flow' of charge (current). This charge is measured in a unit called the Coulomb. Coulombs are not a unit of electrical energy. Electrical energy is measured in a different unit called the Joule.
http://amasci.com/elect/elefaq1.html#ae

 

In the superconductor, current flow was initiated via external magnetic fields which is essentially an electric field being applied on the electrons. i.e. charges only move once a force is applied on them. i.e. no current flow without a voltage field or some external force.

Excellent! You are absolutely right!
Initially matter is neutral (charge carriers, their electrical and magnetic fields, compensate each other). When we make voltage source and electric field, we separate (move) charge carriers mechanically (electrophorus), chemically (galvanic cell) or any other way.
No electric field without moving charge carriers by external force.