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As I'm reading a course on electricity, this one says that an ammeter should be branched inline and not on a bridge. Can someone explain to me physically why we branch a amperemeter inline and a voltmeter on a branch?

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    $\begingroup$ If ammeter is connected abridge, then the current will get divided, and we'll get a wrong reading. Remember - current flows through the conductor, so it is connected inline. voltage is across a conductor, so voltmeter needs to be connected across. $\endgroup$ – user49111 Oct 26 '14 at 17:29
  • $\begingroup$ Also note that most (if not all) voltmeters are actually measuring current through an accurate shunt resistor. $\endgroup$ – K7PEH Oct 26 '14 at 17:32
  • $\begingroup$ Thanks! Can I ask you why we are using shunts to calculate the voltage? It is to be sure that we have the accurate number (because it has nearly no resistance)? $\endgroup$ – Chirac Oct 26 '14 at 17:35
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    $\begingroup$ First, a caveat. There are zillions of ways to measure voltage and current these days using a half-zillion different methods. My comment is mostly to the traditional analog ammeter where the current produces a magnetic field that is used to move an analog needle for measurement. Thus, such analog meters always need a current and the shunt resistance is the method of providing a current path for measuring voltage (note, meter scale is modified to reflect voltage). I suggest that you read the Wikipedia articles on measuring current and voltage. $\endgroup$ – K7PEH Oct 26 '14 at 18:02
  • $\begingroup$ If you want to measure a liquid flow in a given pipe, will you consider the pipe itself, or will you add a secondary path and operate the measure on it ? If you want to measure a pressure difference, how many measurement points are needed ? This + K7PEH comment. $\endgroup$ – TZDZ Nov 4 '14 at 14:21
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The ammeter measure the current flowing through itself. If you want to measure the current flowing through another component, then you must make the current through the ammeter equal to the current through the component. If you wire it in series, that's true. If you wired it in parallel, the current would be unevenly divided between the component and the ammeter.

Similarly: The voltmeter measures the voltage across itself. If you want to measure the voltage across some other component, you must make the two voltages equal. If you wire it in parallel, that's true. If you wired it in series, the voltage would be unevenly divided between the component and the voltmeter.

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