Voltage vs. Amperage

[pianobabe_56]

Whats the difference between the two? I've spent my whole life wondering if there is a simple, easy definition and way to remember the difference between Volts and Amps, and despite all of my physics courses, I still can't figure it out.

Then I remembered all my nerd buddies on PianoForum who know everything. *worships*

[rimv2]

Whats the difference between the two? I've spent my whole life wondering if there is a simple, easy definition and way to remember the difference between Volts and Amps, and despite all of my physics courses, I still can't figure it out.

Then I remembered all my nerd buddies on PianoForum who know everything. *worships*

Think of voltage as the size of the car, and amperage as how many times it runs you over

You can survive being run over once by a large car, but being hit a hundred of times by a small one can do you in.

Not exact but close enough

[thalbergmad]

One was German and the other was French.

[berrt]

Italian: Allessandro Volta

[musik_man]

Voltage deals with energy.  If the difference between two terminals is say 10V, you can find the amount of work done moving a charge across this by multiplying the charge by the voltage.  W=qV

Amps are the unit for current.  Current is defined as charge/time or q/s.  Basically, it tells you how many electrons move through something in a certain time period.

[thalbergmad]

Italian: Allessandro Volta

OK, One was Italian and one was French.

[abell88]

Think of water flowing through a hose. Voltage is the water pressure; the higher the voltage the more pressure. Current/amperage is how fast the water is flowing through the hose.  A big hose with low pressure can still equal a large flow of  water; a small hose with high presssure will still give low water flow.

[contrapunctus]

Amps are the units of measure for how many electrons/sec. are in a current, volts are the units of measure for the strength (energy) pushing the amps. Voltage is determined by the amount of positively charged ions flowing in the opposite direction of the amps. and VxA=Watts.

How did you miss that in highschool? that is third grade stuff.

[cziffra]

How did you miss that in highschool? that is third grade stuff.

you must get punched in the face alot

[quantum]

Randomly:

E = IR

E - voltage
I - current
R - Resistance


P = EI

P - watts


P = (I^2)R

[musik_man]

you must get punched in the face alot

One would hope...  Especially because his explanation of voltage seems wrong.  Voltage is defined as follows V=Int(E,ds,x1,x2)  where E is an electrical field, s is the path, x1 is the starting point and x2 is the end point.  An electrical field is defined as a E=F/q, where F is a force created when a test charge, q, is placed in a field.  The relationship between V and E is roughly the same as the one between Force and Work.  When you see a battery that reads 9V it means that Vp-Vn=9 where Vp is the positive terminal and Vn is the negative.  Vp and Vn are calculated by using 0 for x2 and infinity for x1.

In a circuit, there are no positively flowing ions.  I can't even begin to tell you how wrong that is.  First of all, electrons can easily flow through metal as they exist as a sea surrounding the nuclei.  This is why metals have relatively low resistances.  Positive ions would be virtually impossible to move.  The only substances that move a positive charge are semi-conductors.  Even they don't move positive ions.  Rather 'holes' of no electrons move.(which is in effect a positive current)  What's more, I is defined as the charge per unit time.  If any positive ions moved against the current(how would they even, what mechanism would do this?), they would have to be subtracted from current.  Your explanation is wrong.

You shouldn't berate someone for not knowing a subject that you apparently don't know yourself.

[musik_man]

Quantum, E is not the normal variable for voltage it is the symbol for electrical fields.  V is used for voltage; otherwise, everything you wrote is right.

[quantum]

Quantum, E is not the normal variable for voltage it is the symbol for electrical fields.  V is used for voltage; otherwise, everything you wrote is right.

Old physics book...really old.

[pianolearner]

Whats the difference between the two? I've spent my whole life wondering if there is a simple, easy definition and way to remember the difference between Volts and Amps, and despite all of my physics courses, I still can't figure it out.

Then I remembered all my nerd buddies on PianoForum who know everything. *worships*

Someone has already provided the formula known as Ohms Law. This is the relationship between Voltage, Current (amps), Resistance and power.

V= I x R

Or Voltage = Amps x Resistance

This can be transposed:

Amps = Voltage/Resistance

Resistance = Voltage/Amps

Power is the amount of current times the voltage level at a given point measured in wattage or watts.

Watts = Voltage x Amps


Water is a very good analogy for electricity.

Current is what flows on a wire or conductor like water flowing down a river. Current flows from points of high voltage to points of low voltage on the surface of a conductor. Current is measured in (A) amperes or amps.

Voltage is the difference in electrical potential between two points in a circuit. It's the push or pressure behind current flow through a circuit, and is measured in (V) volts.

Resistance determines how much current will flow through a component. Resistors are used to control voltage and current levels. A very high resistance allows a small amount of current to flow. A very low resistance allows a large amount of current to flow. Resistance is measured in ohms.

Power sockets in the USA are 110Volts. This is the POTENTIAL voltage. Imagine a bucket of water raised up 110 feet high with a tap, no water will flow until the tap is turned. With electricity, no current flows until a load (resistor) is added. A load is anything that draws current, like a light bulb, computer, TV, Blender etc.  When you turn on a 110-Watt light bulb you are placing 110Volts across its filament (which is a load) and it will draw 1Amp (110V x 1A=110W). If the light bulb was only 55 Watts, the same 110V potential is placed across it’s filament but because it is a higher resistance it will draw less current, only 0.5 A, so 55Watts = 110V x 0.5A.

Using Ohms law we can work out what the resistance of the two filaments are:

110W bulb

Resistance = Voltage/Amps

Therefore: Resistance = 110/1
= 110 Ohms

55 Watt bulb
Resistance = Voltage/Amps

Therefore: Resistance = 110/0.5
= 220 Ohms

[timothy42b]

The water analogies are the easiest way to understand though they fall short of a complete explanation.

If you have the math, this is easy.  Maxwell wrote 4 very simple short equations that explain it all.  Faraday did the experimental work that verified these.  Those two giants really produced the theory hundreds of years ago.  The math all works today.  As I said it is simple, but requires calculus.

A couple of points.  Terminology depends on who is using it.  E is universal for college trained people while V is used by mechanics.  College types think current flows from plus to minus while electricians think the other way around.  Electricians talk only about electron flow, while physicists and engineers talk about "charge carriers" in general, which can be electrons, holes, ions, or other. 

Some thing you might not realize:  There is no such thing as voltage.  There is only voltage difference.  A 9 Volt battery has a difference of 9 volts between terminals.  That difference is the pressure which will push electrons through the wire and ions through the battery.  That voltage difference is constant through the life of the battery as it depends only on the materials used.  However the resistance increases and by E=iR the voltage will seem to decrease. 

Electricity travels through wires pretty quickly, near light speed.  There is no apparent lag when you turn on the light switch, even with direct current from a battery.  However the speed of the electrons in the wires is slow, a few mm/sec.  You can turn on a light and walk to it before any electrons get there. 

[pianolearner]

The water analogies are the easiest way to understand though they fall short of a complete explanation.

 

True. But is it necessary to explain horology to someone who only wants to learn how to tell time? 

There is no such thing as voltage.  There is only voltage difference.  A 9 Volt battery has a difference of 9 volts between terminals.

Voltage by definition is the potential difference across a conductor , so it is incorrect to say "voltage difference". Technically you cannot have voltage without current. If you have an energy source such as a battery or regulated power supply the Voltage specified is normally quoted as 'Open Circuit' potential difference. They will usually specify the max current that can be delivered for the particular voltage when a load is attached.

[prometheus]

Moving positive ions, well that is way off

First off no analogy will truely make sense. But when ones interest in physics is low and the math is insufficient is will do.

I was very suprised to read that they teach US college students(?) learn that current flows from positive to negative.

I think other people already covered everything, probably better than I would have done. I would suggest that if people  want to make sure Pianobabe_56 has understood everything you should stop nitpicking and wait for her to ask questions/give feedback on/over the explanations.

[pianolearner]

Moving positive ions, well that is way off

First off no analogy will truely make sense. But when ones interest in physics is low and the math is insufficient is will do.

I was very suprised to read that they teach US college students(?) learn that current flows from positive to negative.

I think other people already covered everything, probably better than I would have done. I would suggest that if people  want to make sure Pianobabe_56 has understood everything you should stop nitpicking and wait for her to ask questions/give feedback on/over the explanations.

Since when has a thread been steered by the original poster? 

[musik_man]

Moving positive ions, well that is way off

First off no analogy will truely make sense. But when ones interest in physics is low and the math is insufficient is will do.

I was very suprised to read that they teach US college students(?) learn that current flows from positive to negative.

I think other people already covered everything, probably better than I would have done. I would suggest that if people  want to make sure Pianobabe_56 has understood everything you should stop nitpicking and wait for her to ask questions/give feedback on/over the explanations.

Current does flow from positive to negative per convention.  It makes the signs a bit easier, even if this isn't what really happens.(cept in certain semi-conductors)

[contrapunctus]

I was just kidding about all the positive ion (cation) stuff. I am glad you caght me.  Electricity is just composed of waves of electrions. Diffraction patterns made by electron waves are really cool.

[timothy42b]

Current does flow from positive to negative per convention.  It makes the signs a bit easier, even if this isn't what really happens.(cept in certain semi-conductors)

Yes. 

In the general case it makes no difference at all.  And college students in physics or engineering are just as likely to be dealing with charge carriers other than electrons as not, so it makes sense.

However in the real world it can occasionally get you in trouble, when diodes are involved and you can't be sure what current convention was used in the manuals.  I had some trouble rewiring a motorcycle once that was caused by that.  I'm still not sure what convention the translated from Japanese service manual used. 

[pianolearner]

Circuit diagrams and their symbols for diodes and transistors usually show conventional current which flows from positive to negative. Anode and Cathode is more appropriate when talking about components. You need to be careful when measuring semiconductors or current with a moving coil analogue multimeter as opposed to a digital mutimeter. Digital mutimeters use conventional thinking, ie/ Positive to Negative. So if you were to measure a diode using a digital multimeter it would conduct when the positive probe is placed on the anode and the negative probe on the cathode. The opposite is true with moving coil analogue multimeters, certainly the older ones.