What exactly is an Amp?

crutschow

Joined Mar 14, 2008
34,280
You may refute an ideal component if you want. It doesn't bother me. MY ideal battery doesn't have discharge resistance.

My ideal components are of a higher quality than yours.

That's all for me here.
I'm glad because your misinformation causes confusion. :rolleyes:
If you have an "ideal" battery than it has neither charge or discharge resistance.
It has no resistance.
 

Marley

Joined Apr 4, 2016
502
Does it meant that the load is the one holding the power instead of the supply voltage? For example a battery does not have power just voltage until it is connected to the load the load will consume what is required and produce the power it needs.
A battery contains energy. When you connect it to an external load resistance, current flows. Power is then dissipated in the load. While this is happening, the amount of energy in the battery reduces.

Think of this like a tank of water on a tall stand. Someone has had to work hard pumping all that water up there. That work is now stored as energy in the tank. Now we run a pipe down to the ground. At the bottom of the pipe is a valve.

With the valve closed, there is a lot of water pressure. This is equivalent to voltage.
But the water is not flowing so there is no current.

Lets connect a water turbine to the outlet of the valve and crack open the valve a bit.

Now the water flows. Now there is current. The turbine spins: power is released in the turbine.
The water level in the tank goes down: the amount of energy left in the tank is reducing.

While the water is flowing, the pressure at the valve reduces.
This is due to the falling head of water and the flow resistance in the pipe: the voltage is falling.

Eventually the tank runs dry. The energy is all used up. All turned into power at the turbine. There is no pressure: no voltage. There is no flow: no current.

The water analogy is a good way of understanding current, voltage, power, energy.
Very important to get a grasp of what these things mean and why they are different.
 

Thread Starter

dante_clericuzzio

Joined Mar 28, 2016
246
A battery contains energy. When you connect it to an external load resistance, current flows. Power is then dissipated in the load. While this is happening, the amount of energy in the battery reduces.

Think of this like a tank of water on a tall stand. Someone has had to work hard pumping all that water up there. That work is now stored as energy in the tank. Now we run a pipe down to the ground. At the bottom of the pipe is a valve.

With the valve closed, there is a lot of water pressure. This is equivalent to voltage.
But the water is not flowing so there is no current.

Lets connect a water turbine to the outlet of the valve and crack open the valve a bit.

Now the water flows. Now there is current. The turbine spins: power is released in the turbine.
The water level in the tank goes down: the amount of energy left in the tank is reducing.

While the water is flowing, the pressure at the valve reduces.
This is due to the falling head of water and the flow resistance in the pipe: the voltage is falling.

Eventually the tank runs dry. The energy is all used up. All turned into power at the turbine. There is no pressure: no voltage. There is no flow: no current.

The water analogy is a good way of understanding current, voltage, power, energy.
Very important to get a grasp of what these things mean and why they are different.
I liked this answer and i think i start to understand what amp is...but i still have some more unanswered questions

1. Let say a charger capable of delivering 5 Amp and the phone is only required 1 Amp...will the phone burnt or only take 1 Amp and charge normally?

2. How do we know and how much amp the 240 AC current that we use at home...why is it seems capable of powering almost any electrical appliance from the smallest to the highest power let say from 1 watt up to maybe 10,000 watts or maybe 100,000 watts..how does the electrical company determine it can do that?
 

Marley

Joined Apr 4, 2016
502
1. Let say a charger capable of delivering 5 Amp and the phone is only required 1 Amp...will the phone burnt or only take 1 Amp and charge normally?
It will only take 1Amp.

2. How do we know and how much amp the 240 AC current that we use at home...why is it seems capable of powering almost any electrical appliance from the smallest to the highest power let say from 1 watt up to maybe 10,000 watts or maybe 100,000 watts..how does the electrical company determine it can do that?
It is not capable of powering any electrical appliance. The maximum current available is limited by the thickness of the wires, the size of the substation transformer, the high-voltage distribution network and ultimately by the size of the distant power station.

If you tried to draw a very large current (by connecting a very low value of load resistance) the wires or the sub-station transformer would overheat and be damaged. That is why you have fuses or circuit breakers in you house.

The electricity supply company decides how much current you are likely to use and installs cables, circuit breakers and transformers to suit.
 

Thread Starter

dante_clericuzzio

Joined Mar 28, 2016
246
It will only take 1Amp.

vs

If you tried to draw a very large current (by connecting a very low value of load resistance) the wires or the sub-station transformer would overheat and be damaged. That is why you have fuses or circuit breakers in you house.
This 2 answers confused me now...if the load only takes what it needs as in the first answer why the second answer it will damaged...since it should only takes what need? This makes me wonder why the all mobile phone charger have different amp rating..i am still confused
 

milmat1

Joined Jun 13, 2016
3
This 2 answers confused me now...if the load only takes what it needs as in the first answer why the second answer it will damaged...since it should only takes what need? This makes me wonder why the all mobile phone charger have different amp rating..i am still confused
The individual phone will have different circuitry as well as different size batteries. But the end result will be the same. No matter what the charger is capable of, the internal resistance of the phones charging circuit will determine how much current flows into the battery to charge it. BUT this does not say that all that current is always available from the charger !!
Leys say you connect a charger of 100 milliamp, (0.100 amp) Well its going to take a lot longer to charge a 2 amp/hour battery than if it were a 1 amp charger......
So the higher available current from a charger may charge the battery faster, Keep in mind there will be heat to deal with as well. A Slow charge is usually better for the battery, but in our fast paced world we want to charge our battery quickly. And so we suffer the loss of battery life.....
The higher output current
 

wayneh

Joined Sep 9, 2010
17,496
1. Let say a charger capable of delivering 5 Amp and the phone is only required 1 Amp...will the phone burnt or only take 1 Amp and charge normally?
That may be one of the top ten questions asked repeatedly in this forum. The answer is that everything is fine as long as the supply exceeds the demand. If the supply can handle 5A and the load demands 1A, no problem. If the supply is rated to 1A and the load wants 5A, big problem.

It's like the power available at your wall plug. Anything from a tiny nightlight up to a 1500W space heater is acceptable. The nightlight does not care that the wall plug can supply enough power for 100 more nightlights, or a million more. It just knows that there is adequate power. If you plug in any load larger than the space heater, a circuit breaker will blow to protect the wiring in your home (and your home from catching on fire).
 

nsaspook

Joined Aug 27, 2009
13,079
The water analogy is a good way of understanding current, voltage, power, energy.
Very important to get a grasp of what these things mean and why they are different.
One of my pet peeves, not directed at you. The water analogy because of it's limited partial nature (and usually a lack of knowledge of closed loop fluid flow in pipes), only causes deep misconceptions of the general electro-mechanical work relationships of current, voltage, power and energy. Potential difference (Potential and potential energy are position dependent) is often explained as a difference in pressure (energy per unit volume independent of position) across either side of the load with constrictions as resistors. Try to explain in any detail why there is a difference in pressure? What is it? What physical property of water makes the pressure different? What's the distinction from water that goes round and the transfer of 'pressure'?

"Eventually the tank runs dry. The energy is all used up." is a good example. It's seems perfectly logical to say this with linear DC circuits but as soon as you get to the next chapter in learning about AC currents the bottom falls out of the tank when we start to directly relate current flow direction to energy flow direction.
 
Last edited:

WBahn

Joined Mar 31, 2012
29,976
This 2 answers confused me now...if the load only takes what it needs as in the first answer why the second answer it will damaged...since it should only takes what need? This makes me wonder why the all mobile phone charger have different amp rating..i am still confused
If you short the wires (or try to power an entire auto assembly line from your house's wiring) the amount of current it needs would be thousands and thousands of amperes. Without the breakers in place, that would so far exceed the capabilities of the service provided to your house that the wiring and/or transformers would be damaged in the attempt to supply it.

Your car has an engine in it that has a certain horsepower rating. But when you are tolling down the road at a moderate speed (i.e., well below the car's top speed) are you using that full amount of power? No. So you control how much power the engine is actually giving out using the gas pedal. Now, if I took your car's engine and put it into a fully loaded eighteen-wheeler, do you think it would be able to pull that rig down the road at that same speed? Almost certainly not. That's because that engine's output capability (the horsepower rating) is less than the horsepower needed to move the big rig.

So if you have two mobile phones, one that is designed to charge slowly at, say, 1 A of current and the other that is designed to charge rapidly at, say, 5 A of current, then if you have a charger that is rated at 2 A (meaning that that is the maximum output that it is capable of delivering) that it can charge the first phone but not the second (unless the second is designed to be content with a lower charging rate and adapt it's current needs accordingly).
 

wayneh

Joined Sep 9, 2010
17,496
One of my pet peeves, not directed at you. The water analogy because of it's limited partial nature ...
It's very handy for visualizing a few concepts but falls apart in others, like inductance and the closed loop issue.

One thing I've noticed with some surprise is how many students – and working professionals – have a very hard time with units and dimensional analysis. I can remember professors describing how one unit times another gave a third, with the dimensions cancelling top to bottom. Most of the class would glaze over. When he would bring it back to an example, like mph times hours gives miles, some of the class would make the connection, at least for the moment, and "get it". A few never would.

I think the primary value of the water analogy is that it provides that dimensional awareness, that flow rate times elapsed time equals a quantity, all in terms of something familiar. It's like the mph x hours example. If the students all had a good grasp of dimensional analysis before learning electronics, you wouldn't need analogies to more familiar fields.
 

WBahn

Joined Mar 31, 2012
29,976
1 ampere = 6,241,510,000,000,000,000 electrons per second.
An ampere is a measure of how many electrons move past a point every second.
While certainly good enough for most purposes, it's actually more like

1 A ~= -6,241,509,126,000,000,000 electrons per second since the electronic charge is currently known to about 11 sig figs.

Interestingly, there is a proposal to redefine the electronic charge as a fixed constant (-1.60217E-19 A·s), which is actually a fairly significant change as it would make one ampere

1 A ~= -6,241,534,918,267,100,245.3 electrons per second

It would also make other constants, such as the permeability of free space, no longer exactly expressible.

I don't see the value of the redefinition. I would see it a bit better if they defined the ampere to be a fixed number of electrons per second and then used that to define the kilogram.
 

WBahn

Joined Mar 31, 2012
29,976
You may refute an ideal component if you want. It doesn't bother me. MY ideal battery doesn't have discharge resistance.

My ideal components are of a higher quality than yours.

That's all for me here.
Well, MY ideal battery doesn't have charge resistance, either. So THERE!
 
The 6 megaWatt power plant that provides power to your home is more than you need. That's the key, the DC adpater. as built, can supply a certain amount of current and Voltage just like the power plant.

The power plant provides regulation my basically throttling natural gas generators and other ways.
 

nsaspook

Joined Aug 27, 2009
13,079
I think the primary value of the water analogy is that it provides that dimensional awareness, that flow rate times elapsed time equals a quantity, all in terms of something familiar. It's like the mph x hours example. If the students all had a good grasp of dimensional analysis before learning electronics, you wouldn't need analogies to more familiar fields.
I understand but most beginning students are most familiar with facets, open-ended hoses, buckets and tubs so their dimensional awareness of current in this view is that of a mass/charge that's not conserved because they intuitively know that water has momentum as it moves out the nozzle as the energy carrier in a tank ready to be lost on the other end of the pipe down the sewer or ground after the 'work' is done. Until you get to electron guns or high voltage circuits that's not the way electricity works as the KE of the electrons (current) is essentially irrelevant for most circuits.
 
nsaspook:

Your right, electron guns and thermonic emission is a totally different concept than a wire.

Electrons really don't flow in a wire. Net charge does. then there's that "conventional current" thing. Positive to Negative. Do a search on "Ben Franklin conventional current".

Electrons, kinda collide with each other, sort of like "bumping cars in a carnival" with lots of pushes with "Voltage". In the process of moving, heat is created.
 

GopherT

Joined Nov 23, 2012
8,009
While certainly good enough for most purposes, it's actually more like

1 A ~= -6,241,509,126,000,000,000 electrons per second since the electronic charge is currently known to about 11 sig figs.

Interestingly, there is a proposal to redefine the electronic charge as a fixed constant (-1.60217E-19 A·s), which is actually a fairly significant change as it would make one ampere

1 A ~= -6,241,534,918,267,100,245.3 electrons per second

It would also make other constants, such as the permeability of free space, no longer exactly expressible.

I don't see the value of the redefinition. I would see it a bit better if they defined the ampere to be a fixed number of electrons per second and then used that to define the kilogram.
Are you:

a) :p:D:p:D:p:D:p:D:p a comedian, :p:D:p:D:p:D:p:D:p

b) some kind of troll

c) :oops:a victim of Asperger's Syndrome

d) other?


A whole paragraph for part-per-billions rounding error? I don't want to start laughing and be mean in case the answer is "c". If it is "c", I am truly interested in how do you make it through a day if this amount of "error" was worth a paragraph?

Do you do things like carefully select items when shopping so the total can be multiplied by the 2.9% state sales tax comes out to a perfect cent with no rounding error? Do you bring your own certified scale to the market when you buy blueberries to make sure you are not getting ripped off? Do you record your odometer and fuel purchases in a little notebook - then calculate and record your mileage to 11 digits of "accuracy"?
 

nsaspook

Joined Aug 27, 2009
13,079
The Qu-Ampere is big news in semiconductor metrology for future devices. The amount of uncertainty with the current standard seems small until you start dealing with nano-scale components that need meters calibrated with primary current standards in attoamperes.

http://www.eurekalert.org/pub_releases/2014-03/pb-hpf033114.php
The ampere has for long been a problematic unit: in spite of its being a base unit - and thus a basis for all electric measurements - it can only indirectly be realized in a metrologically accurate way via the derived electric units the volt and the ohm. Those two units can be accurately realized on the basis of fundamental constants - the Josephson constant (for the volt) and the von Klitzing constant (for the ohm). Scientists worldwide have been putting great effort into doing the same with the ampere with the appropriate fundamental constant being the charge of a single electron. A quantum standard for the ampere could in principle be realized by controlling the capturing and emission of single electrons in an electronic nano-circuit. The circuit could then serve as a so-called "single-electron pump", a device which was first designed in the 1990s. However, only recently, scientists from PTB have developed an optimized single-electron pump allowing both the generation of a clocked single-electron current and its independent measurement with minimum uncertainty.
 

GopherT

Joined Nov 23, 2012
8,009
The Qu-Ampere is big news in semiconductor metrology for future devices. The amount of uncertainty with the current standard seems small until you start dealing with nano-scale components that need meters calibrated with primary current standards in attoamperes.

http://www.eurekalert.org/pub_releases/2014-03/pb-hpf033114.php
That may be true but this guy is asking "what EXACTLY is an Amp?" When it is obvious he means, "can you help me understand what an Amp is?" ...in terms and numbers he can understand.
 
Top