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Connection Of Appliances

  1. Jan 29, 2012 #1
    Moving from a schematic diagram to real circuits.
    I have a few questions:
    Since the ammeter should be connected in series, why should the positive pole of a battery be connected to the ammeter's "positive" plug. Won't it be connected in parallel that way?
    If you didn't get what I mean see the first figure in this link: http://www.allaboutcircuits.com/vol_6/chpt_2/4.html (Follow the wires)

    And then another thing, we know that the resistor like the capacitor like the switch doesn't have a negative plug or a positive one.. Then how will I know how should I connect the appliance that follows if it has those "+ve -ve" PLUGS?

    I mean how should I know where to plug in the connection wire?
    I will be grateful for any descriptive answer, or link, or whatsoever.
  2. jcsd
  3. Jan 29, 2012 #2
    If you were building DC ammeters, how would you mark the terminal that should be connected to the positive side of the battery? Won't it be connected in parallel with what?

    Large capacitors usually are marked with a positive and negative terminal. If a component isn't marked, it usually doesn't make any difference. Just like the ammeter, appliances with plugs marked +ve and -ve should be connected to the the positive and negative sides of the battery respectively.

    I mean how should I know where to plug in the connection wire?[/QUOTE]
    This question isn't sufficiently descriptive to be meaningful.
  4. Jan 29, 2012 #3

    jim hardy

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    have you forgot definition of series?

    'all current going through one must go thru other...'
    so in your mind's eye walk around that circuit
    sure looks like series to me.
  5. Jan 30, 2012 #4
    The circuit in your link is COMPLETELY WRONG !!!!!
    they have the current flowing out of the - terminal of the battery and into the + terminal. This is wrong.
    The ammeter in the first diagram is correct with red terminal to the + on the battery.
    I am going back to look at this site and see what is written.
    Last edited: Jan 30, 2012
  6. Jan 30, 2012 #5
    I have looked at the link again. Their breadboard diagrams are correct so I would assume that whoever drew the diagram with the battery and current arrows made a bad mistake.
    In their write up they mention 'the flow of electrons'..... current is a flow of electrons but the current direction is not the direction of flow of electrons !!!!!!!!!
  7. Jan 30, 2012 #6


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    M. next:
    the ammeter shown in the link is connected in series and will measure the current flowing through the circuit. As you said, “Follow the wires” from the battery, through the ammeter, through the lamp (load) and then back to the battery. The picture is exactly the same as the schematic diagram.

    The polarity of the meter probes is correct in every one of the diagrams.

    I disagree with using those current arrows on the Short Circuit diagram. Just forget current arrows, they will only confuse you. It is NOT important to understand electronics.

    Resistors are “passive” components. You could install a resistor in a circuit in either direction and would make no difference. The resistance will be the same.

    Some capacitors have polarity markings on them. Installing these you must observe the correct polarity. Other capacitors are NOT polarized, which means you can install it either way.

    Switches are mechanical devices for connecting/disconnecting a conductor to/from another part of the circuit. None are polarized.
  8. Jan 30, 2012 #7
    This is strange advice to give to anyone seeking explanations in electronics
  9. Jan 30, 2012 #8
    Greetings there..
    Excuse my late response.
    I noticed that I have been misunderstood, or the question was not clear enough. That's why I ll draw what I mean.

    Probably I mixed up the concept. If you would help me organize it

    Attached Files:

    Last edited: Jan 30, 2012
  10. Jan 30, 2012 #9
    If you add the voltage across every component in a circuit, including the battery, the sum should always equal zero. Try that for the circuit on the left and for your circuits on the right. You don't need to know the actual voltages in this case just that the voltages across all the non-battery components must equal the voltage across the battery.
  11. Jan 30, 2012 #10
    How is this an answer to my question? What does Kirschoff's Voltage Addition Theorem has to do with positive and negative signs I placed on the right side of the picture?
    Tell me if my question isn't clear enough.
  12. Jan 30, 2012 #11
    With the diagram on the left starting at the positive terminal of the battery going counterclockwise.

    resistor + - 1 volt (assumed for sake of example)
    ammeter + - 0.005 volt
    switch (closed) + - 0.005 volt
    resistor + - 1.990 volts
    battery - + 3 volts

    sum 0 volts

    With the diagram on the right (top) starting at the positive terminal of the battery going counterclockwise.

    resistor - + 1 volt (assumed for sake of example)
    ammeter - + 0.005 volt
    switch (closed) - + 0.005 volt
    resistor - + 1.990 volts
    battery - + 3 volts

    sum 6 volts

    Do you see the difference?
  13. Jan 30, 2012 #12


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    M. next, Excuse me please for my error in post #6 above when I suggested you "Just forget current arrows, they will only confuse you. It is NOT important to understand electronics."

    As technician points out, this is not how to help folks who are beginning their study of electricity. There have been multiple threads here on PF exactly about this concept. I offer two sources that describe the "diirection of current flow" for you.

    “In metallic solids, electricity flows by means of electrons, from lower to higher electrical potential. In other media, any stream of charged objects may constitute an electric current. To provide a definition of current that is independent of the type of charge carriers flowing, conventional current is defined to flow in the same direction as positive charges. So in metals where the charge carriers (electrons) are negative, conventional current flows in the opposite direction as the electrons. In conductors where the charge carriers are positive, conventional current flows in the same direction as the charge carriers.”


    “…the misconception that "Electricity" is made of negatively-charged particles called electrons. This fundamental error leads most people to imagine that electric currents are always a flow of negative particles. Actually, in some conductors the electric currents are a flow of genuinely positive charges, while in others the flows are indeed negative particles. And sometimes the currents are both positive and negative particles flowing at once, but in opposite directions within the same conductor. We cannot arbitrarily decide which way the charges flow, since their true direction always depends on the type of conductive material.

    To gain some insight, let's examine the details. When trying to understand electric circuits and electrical measurements, we need a simple way to take measurements of the important entity named Electric Current. But to measure currents, won't we first need to measure how much of the current is composed negative particles going one way, and positive particles the other? Yes, but we ONLY need this if we want to know EVERYTHING about the electric current. The flowing negatives and positives are usually not equal, and the speed of the positives in one direction is usually not the same as the speed of the negatives in the other. Electric current can be complicated! However, there is a cute trick we can pull in order to avoid having to look at the particles at all. And that trick holds the answer to the question.

    Electric currents produce three main effects: magnetism, heating, and the voltage drop across resistive conductors. These three effects cover almost everything we encounter in electronics. And these three effects don't care about the amounts of positive and negative particles, or about their speed, their mass, their charge, etc. If a hundred positive particles flow to the left per second, this gives EXACTLY as much magnetism, heating, and voltage as a hundred NEGATIVE particles flowing to the right per second. (Note: this is because reversing the polarity of the particles reverses the current, and reversing the particle direction reverses the current again! Two negatives make a positive.) Magnetism, heating, and voltage drop together represent nearly every feature that's important in everyday electrical circuitry. THEREFORE, AS FAR AS MOST ELECTRICAL DEVICES AND CIRCUITS ARE CONCERNED, IT MAKES NO DIFFERENCE IF THE CURRENT IS MADE OF POSITIVE PARTICLES GOING ONE WAY, OR NEGATIVE PARTICLES GOING THE OTHER... OR HALF AS MANY NEGATIVES FLOWING BACKWARDS THROUGH A CROWD OF HALF AS MANY POSITIVES.

    So, in order to simplify our measurements and our mental picture of Electric Currents, we cut away the unused parts of the picture. We make the negative particles positive, then add their current to any positive particles which were flowing forward. We stop thinking of current as being a flow of charges. Instead we intentionally define "electric current" as being a flow of exclusively positive particles flowing in one particular direction. We don't care about the real polarity of the particles. We don't care about their speed, and we don't care about their number. We ignore both the chemical effects and the effects of the velocity and direction moving particles. We ignore the collisions between positive and negative particles. All we care about is the total net charge which moves past a particular point in the circuit. The real charges are too complicated to deal with, and the added complexity gets us very little information as long as we're only interested in voltage drop, magnetic fields, and heating.”

  14. Jan 30, 2012 #13
    Bobbywhy has made some good points about 'electric current'
    One thing worth noting is that an electric current was defined before electrons were discovered. All of the rules about direction of force on a wire carrying a current in a magnetic field etc are based on a current being a flow of + charges. It is an (unfortunate) accident that the charges flowing in metals are electrons which we all know are -charged.
    If you are a chemist and deal with electrolysis you will know that current can be the flow of electrons in one direction and +ve ions in the opposite direction.
    In Intrinsic semiconductors the current is due to -ve electrons in one direction and +ve holes in the opposite direction.
    One thing is for sure.... CONVENTIONAL current is taken to be the way + charges flow and that is from (out of) the + terminal of a cell to (into) the - terminal of a cell.
    This is the only thing wrong on that site that was given.
    Last edited: Jan 30, 2012
  15. Jan 30, 2012 #14
    Skeptic2, thank you for clearing up your answer. You were really helpful.
    Bobbywhy, it's not a problem at all, I didn't even take it into real consideration (thinking it might slipped out), untill technician pointed it out. No worries :)
    Thank you for your time, and patience.
    As for technician, I ll keep this note in mind. Thanks :)
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