Current Flow in circuits?

Discussion in 'General Electronics Chat' started by Snapester, Apr 9, 2012.

  1. Snapester

    Thread Starter New Member

    Apr 9, 2012
    Hi guys, im a new member and just started getting into electronics, i have been reading alot but im having a problem grasping the issue of how the current flows through the circuit? I work with AC current mainly which flows + - but how does DC flow through circuit as it seems to flow everywhere?
    Does anyone have any good resources or could help me out?
  2. BSomer


    Dec 28, 2011
    There are two different theories on this. One is looking at it from the electron point of view which is - to +. The other is conventional, which is + to -. They both are right. Some of the more knowledgable members can shed some more light on this subject.

    However, you should be prepared for those that say current doesn't flow, electrons flow. Technically they are right, as current is the flow of electrons. I am not going to get into this though.

    Your statement about the current flow in AC is incorrect though. The current direction in AC circuits is bi-directional, hence the name Alternating Current.
  3. Snapester

    Thread Starter New Member

    Apr 9, 2012
    Yes i know that AC is bi-directional and works in pulses so its either - or + but my main concern was with how DC flows in a circuit i don't get it?
  4. bretm


    Feb 6, 2012
    The general idea is that with AC the direction of the current is repeatedly reversing direction. With DC, the direction of the current keeps going in the same direction (assuming everything else is constant). That's really the only difference.
  5. vpoko

    Active Member

    Jan 5, 2012
    In actuality, charge carriers in a metal are electrons, which flow from an area with an abundance of electrons (-) to an area with a dearth of them (+). In other materials, say the human body, in which ions - positive and negative - are the charge carriers, the charge carriers could flow in either direction (negative ones behave like electrons, positive ones flow from + to -). This is also true in semiconductors where charge carriers can be holes, which are positive (relative to the electrons surrounding them).

    When using electricity, we generally care about resistive loads, which give us things like heat and light, and magnetic fields created by moving, charged particles. The resistive load obviously doesn't care which way charge carriers are moving, a light bulb would work wired either way. Magnetic fields are reversed when the direction of charge carrier flow past a point is reversed, but it's also reversed when the polarity is reversed. Because of the double reversal, negative charge flowing from - to + has the same effect as positive charge flowing from + to -, and "true" direction of charge flow can be ignored. For convention's sake, most sources treat current as flowing from + to - (called "conventional current"), though there are exceptions, including the tutorials here at AAC. When looking at components like diodes, you'll find the stripe is on the cathode side, which is the side conventional current exits the diode. In reality, electrons are flowing into that side, but it's not important.
  6. studiot

    AAC Fanatic!

    Nov 9, 2007
    Direct current, Alternating current and pulsed current are all different.

    When you study circuits from an electrical or electronic engineering point of view it is best to (temporarily) abandon consideration of the physics of current flow.

    Current flow in circuits from an engineering point of view is a formalised model of reality set up for ease of calculation.

    From an engineering point of view a circuit is a collection or assemblage of components connected together in some way. The particular way is called the circuit topology.

    One of these components is a source of electricity. There are several different types of source, voltage or current, alternating or unidirectional, steady or varying, pulsed or continuous and so on.

    Direct current is unidirectional and continuous.

    The connection points of components are called terminals. Sources have at least 2 such terminals, sometimes more.

    Current is considered leave one terminal, pass through the assembly of circuit components and return to the source at its other terminal.

    For a source of direct current one terminal was labelled positive (+) and one negative (-) a long time ago.

    Engineering has considered current to leave the source by the + terminal and re enter by the - terminal for about a century.

    Recently there has been a move to reverse this idea for reasons of physics and this new convention is supported by this site All About Circuits in its online textbook.

    Most engineers use the older convention.

    Does this help and can you expand upon your query?
  7. crutschow


    Mar 14, 2008
    So what don't you get?

    I know some don't like the analogy but in a simple fashion you can think of current as the flow of water through a pipe from the output of a pump (voltage source), through the plumbing and back to the input of the pump. Current flows from the positive side of the source, through the circuit and back to the negative side of the source (this is for normal current direction, not electrons). The current must always have a complete path from the positive side of the source back to the negative side.

    Make sense?