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#128571 - 06/08/03 11:00 PM amperes  
electricman03  Offline
Junior Member
Joined: Jun 2003
Posts: 6
i understand that volts is how many electrons are in one body, but i dont understand amps. is amps how fast electrons flow through a conductor, or how many? and if it is how many, then im confused about coulumbs. and if its how fast, do you find amps by the length of the whole conductor? im so confused help is very much appreciated

thanks, scott


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#128572 - 06/08/03 11:58 PM Re: amperes  
Scott35  Offline

Broom Pusher and
Member
Joined: Oct 2000
Posts: 2,707
Anaheim, CA. USA
Here's a "quickee":

Voltage (Electromotive Force or the symbol "E"):
Electrical "Pressure". The "Pressure" resulting from the Potential Difference of the opposite polarity points of a power supply (very, very basic description!),

Amperes (Intensity of currents flowing in a closed circuit - Symbol = "I"):
The level of current flowing at a given point on a circuit. 1 Ampere is 6.28 x 10^19 (I think that's right) Electrons flowing across a given point in one second. This equals 1 Coulomb (sp???).

Ohms law dictates that on a fixed Resistance, the level of current ("I") which will flow across that Resistance ("R"), is dependant on the Impressed Voltage ("E"). The combination of E × I on this type of circuit results in a level of True Power ("P") - measured in Wattage - being delivered from the power supply and dispersed into the load element.

Example:
Circuit with 10 Ohm Resistor connected to a 10VDC power supply, results in one ampere flowing in the circuit - delivering 10 watts of true power to the load Resistor.

Formula:

I = E ÷ R
or simply 10 Volts pushes 1 Amp across a 10 Ohm Resistance.

P = E × I
or simply 10 Volts times 1 Amp equals 10 watts

Good luck!

Scott35


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#128573 - 06/10/03 03:26 PM Re: amperes  
Bill Addiss  Offline
Member
Joined: Oct 2000
Posts: 3,875
NY, USA
Here's a link to some info on this subject. If you root around that website more you should be able to find more answers to some of the other questions you have too.
http://science.howstuffworks.com/question501.htm

Bill


#128574 - 06/12/03 05:26 PM Re: amperes  
PCBelarge  Offline
Member
Joined: Jun 2003
Posts: 681
Dobbs Ferry, NY, USA
Electricman03,

Try thinking like this, When you turn the water on in a hose there is a certain amount of pressure, as you turn on more pressure, more water comes out. That is the voltage, more pressure, more voltage.

As you apply pressure, water flows, that is current. The amount of water flow is like the amount of current flow.

Maybe that will help

Pierre


Pierre Belarge

#128575 - 08/19/03 01:25 PM Re: amperes  
cavil  Offline
Junior Member
Joined: Aug 2003
Posts: 6
The volt is a unit of electric potential. It is fundamentally energy per unit charge (joules per coulomb). When we measure a voltage with a voltmeter it reads the electric potential difference between two points. This is the amount of energy in joules that one coulomb of electric charge would acquire if it moved from the point of higher potential to lower potential under the action of the electrostatic coulomb force.

A good way to think about this is to use the idea of gravitational potential which (close to the earth's surface) is proportional to height. A point at the top of a hill is at a higher potential (gravitational voltage as it were) than a lower point. Some mass e.g. water can naturally flow from high potential to low potential. It would be a CURRENT of mass. Similarly charge flowing from high potential to low constitutes an electric current. It is a flow rate of charge in coulombs per sec or gallons per minute in plumbing. The coulomb per second is called an ampere.

High currents do not necessarily mean high speeds of the charges themselves. In typical wiring the average "drift rate" of charge for DC is less than one inch per second.


#128576 - 09/05/03 01:10 PM Re: amperes  
JohnS  Offline
Member
Joined: Jul 2003
Posts: 36
Cleveland, Ohio USA
The ampere (A)is an SI base unit and is defined as:

"The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 metre apart in vacuum, would produce between these conductors a force equal to 2 × 10-7 newton per metre of length."

The volt (V) is an SI derived unit and is defined as:

the SI unit of electric potential. Separating electric charges creates potential energy, which can be measured in energy units such as joules. Electric potential is defined as the amount of potential energy present per unit of charge. Electric potential is measured in volts, with one volt representing a potential of one joule per coulomb of charge. The name of the unit honors the Italian scientist Count Alessandro Volta (1745-1827), the inventor of the first battery.

See: http://www.unc.edu/~rowlett/units/

for further info on units

Quote
High currents do not necessarily mean high speeds of the charges themselves. In typical wiring the average "drift rate" of charge for DC is less than one inch per second.


Where did you get the inch per second figure from? I understand and prefer to know these things in SI units. I loathe converting FFU (Fred Flintstone Units) to SI as their is a high probabilty the FFU is wrong to begin with. There is a tendancy when converting SI to FFU to round the result to give the impression of neat numbers in FFU. Thus, when attempting to return to SI, the numbers are not the original.

Electric current is indirectly a measure of the number of electrons passing a given reference point in a unit time of one second. Since the ampere is also equal to (but not defined as) one coulomb of charge moving per second, and there is a fixed number of electrons per coulomb (approximately 6.241 506 x 10^18), one can see that current is the amount of electrons moving and not the speed at which they move (speed being in units of metres per second).

The actual electron speed varies with the medium it is moving through and I believe it is equal to the speed of light when in space (299 792 458 m/s exactly).

coulomb (C)
the SI unit of electric charge. One coulomb is the amount of charge accumulated in one second by a current of one ampere. Electricity is actually a flow of particles called electrons, and one coulomb represents the charge on approximately 6.241 506 x 10^18 electrons. The coulomb is named for a French physicist, Charles-Augustin de Coulomb (1736-1806), who was the first to measure accurately the forces exerted between electric charges.


#128577 - 10/02/03 01:44 AM Re: amperes  
cavil  Offline
Junior Member
Joined: Aug 2003
Posts: 6
The slow drift rate of charge is a well known result. (See any elementary university physics text). For a copper wire with a density of 8.95 g/cm^3 and cross-sectional area of 3 x 10^-6 m^2 carrying 10A the drift rate turns out to be about 0.25 mm/s. Do not confuse this with the average speed of electrons between collisions which is much higher.

Electrons have mass and so can never travel at the speed of light. The electric field, such as the one turned on when you flip a switch, does propagate at a speed close to that of light.



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