Current flow direction in circuit

[apurvmj]

Hi all,

I'm having a small question about current flow direction indication in circuit diagrams.

Its shown as current flow from +ve pole to -ve pole, but -ve pole has higher electron concentration (potential) & electrons flow from -ve to +ve.

Whats the logic of showing the direction of current flowing in opposite way.

Hope I have made myself clear.

Waiting for reply.

Thanks.

[Spyman]

Conventions

A flow of positive charges gives the same electric current, and has the same effect in a circuit, as an equal flow of negative charges in the opposite direction. Since current can be the flow of either positive or negative charges, or both, a convention for the direction of current which is independent of the type of charge carriers is needed. The direction of conventional current is defined arbitrarily to be the direction of the flow of positive charges.

 

In metals, which make up the wires and other conductors in most electrical circuits, the positive charges are immobile, and the charge carriers are electrons. Because the electron carries negative charge, the electron motion in a metal conductor is in the direction opposite to that of conventional (or electric) current.

 

Reference direction

When analyzing electrical circuits, the actual direction of current through a specific circuit element is usually unknown. Consequently, each circuit element is assigned a current variable with an arbitrarily chosen reference direction. When the circuit is solved, the circuit element currents may have positive or negative values. A negative value means that the actual direction of current through that circuit element is opposite that of the chosen reference direction. In electronic circuits the reference current directions are usually chosen so that all currents flow toward ground. This often matches conventional current direction, because in many circuits the power supply voltage is positive with respect to ground.

 

http://en.wikipedia.org/wiki/Electrical_current#Conventions

[apurvmj]

How can we explain +ve charge in AC or DC generator?

Coz in magnetic field only electron that moves.

Also in lightening strike, as heavily -vely charged clouds discharges to neutral ground. Ground is not +vely charged I guess.

Pls correct me if I'm wrong.

[Spyman]

You can choose a reference point from where you measure a differential charge to another point in the circuit whereever you like, but usually it is the negative pole that is chosen as ground.

 

In electrical engineering, ground or earth is the reference point in an electrical circuit from which other voltages are measured, or is a common return path for electric current, or a direct physical connection to the Earth.

http://en.wikipedia.org/wiki/Ground_(electricity)

 

 

Don't know much about lightning but here are two seeminly revelant quotes with links to different chapters on the Wikipedia page of lightning:

 

Unlike the far more common "negative" lightning, positive lightning occurs when a positive charge is carried by the top of the clouds (generally anvil clouds) rather than the ground. (...) Positive lightning makes up less than 5% of all lightning strikes.

http://en.wikipedia.org/wiki/Lightning#Positive_lightning

 

As a thundercloud moves over the surface of the Earth, an electric charge equal to but opposite the charge of the base of the thundercloud is induced in the Earth below the cloud. The induced ground charge follows the movement of the cloud, remaining underneath it.

http://en.wikipedia.org/wiki/Lightning#Leader_formation_and_the_return_stroke

Edited June 13, 2012 by Spyman

[Enthalpy]

...It's shown as current flow from +ve pole to -ve pole, but -ve pole has higher electron concentration (potential) & electrons flow from -ve to +ve.

Whats the logic of showing the direction of current flowing in opposite way...

 

It's because electrons have a negative charge. This megastupid convention was taken as physicists still didn't know about electrons.

[Joatmon]

...............Coz in magnetic field only electron that moves..................

.................Pls correct me if I'm wrong.

Just a small detail. In different materials there is movement by what are termed positive charge carriers from positive to negative. In liquids they may be ions, in metals and semi-conductors they are known as holes. Basically a hole can be thought of as a place just vacated by an electron. Holes are rather strange as they are not really objects but spaces where objects (i.e. electrons) would be attracted to. If you are dealing with basic electrical circuits just tuck this away at the back of your mind for now. If you want more information just follow the link.

 

http://en.wikipedia.org/wiki/Charge_carrier

 

 

[burhan hafiz]

it is used only because of a convention and it is thus called a conventional current

 

Edited July 22, 2012 by burhan hafiz