question about breaking +/- leads

Discussion in 'General Electronics Chat' started by lexmark, Dec 17, 2005.

  1. lexmark

    Thread Starter New Member

    Dec 17, 2005
    Hello everyone!

    This is my first post here. Im a freshman student taking electrical engineering, and I am just starting out in my journey of electrical systems! I hope that later on I can contribute to the community here, but Im still learning the basics lol. I am hoping that someone here could answer a question that has been on my mind lately.

    From my understanding, the conventional flow method is the most widely used. This means that the change from positive charge to negative charge shows the direction of the current flow. In reality however, the electrons repel from - and flow to +.

    My question is, when i am working with a circuit board and want to make an adjustment to my circuit ( remove a resistor for example) with leads coming from an active power supply, why is it that I am suppose to disconnect the red alligator lead (+) instead of where the electrons are coming from (-)? Won't the electrons coming from - flow try to flow to my skin, or anything with a positive net charge? Why shouldn't I make a break where the electrons are flowing from?

  2. alva


    Dec 14, 2005
    Hello there. Not to be flippant but why not turn the circuit off to make sure there aren't electrons flowing through your skin? In a very low voltage battery situation it won't matter but it's a bad habit to get in to when higher voltages are around!

    I believe conventional current is mainly used for easier calculation of circuits since there are less negative numbers than if you use electron flow calculations.
    And as for free electrons, they are everywhere a conductor is, even if there is no current. When a voltage source is applied to a conductor the electrons align and start pushing each other toward the positive charge all along the conductor simultaneously and at a relatively slow rate individually but with the net effect of current flowing at the speed of light.
  3. n9xv

    Senior Member

    Jan 18, 2005
    Hi Lexmark,

    Assuming the black (negative) lead to be at ground potential;

    the reason for disconnecting the red (positive) lead from a circuit is because the positive lead carries the voltage on it. With the red lead connected, the circuit is still "live". You could easily short something out, or if the voltage was high enough, you could be shocked or injured. With only the black (ground) lead connected, there is no "possible" paths for current to flow.
  4. Gorgon

    AAC Fanatic!

    Aug 14, 2005
    Hi Lexmark,
    You should take care when you are working on logic designs. If you cut power on parts of the circuit only, you may overload and wreck the logic parts connecting the the powered and the unpowered circuit. The unpowered logic will be powered through the input protection circuits from the active outputs in the powered part. Depending on the power requirement of the unpowered part you may fry the chips.

    So, a golden rule is never to power a design/ circuit partially! (without knowing what the result is.)

    TOK ;)
  5. buddyengineers


    Mar 19, 2005
    Hi frnd...,
    A newbie never mind.., welcome to the place where u can share wat u learn.
    As for ur query is considered..., a good question.
    Now u hav learnt tht electroncs flow thru the negative, and are attracted towards the positive. But we always follow the reverse logic..., mind u ALWAYS.
    So instead of grounding the +ve of the battery..., we gnd the negative of the battery. (Thts wat is the reverse funda).
    Now u must ask y do we gnd the -ve terminal, bcoz v want some point as reference, and we take Earth as reference.
    Now as i said.., in most of the electronic circuits, the -ve is gnded, so both are at the same potential. U must know tht the -ve of the battery is at zero potential and also gnd is at zero potential.
    And when u r working on a circuit, and u dnt disconnec the -ve terminal, and if u touch the -ve terminal, wat will happen is tht: U are at gnd potential, and the battery -ve is at gnd potential. So no Potential Difference.., so no current.

    So remember one thing always tht for current to flow u always need a potential difference. As water cannot flow when both the levels are same. Current cant flow between two same potentials.

    I hope i hav been of some assistance to u.
    Have a nice time.