Why are ammeters used in series and voltmeters in parallel?

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?

• 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. – user49111 Oct 26 '14 at 17:29
• Also note that most (if not all) voltmeters are actually measuring current through an accurate shunt resistor. – K7PEH Oct 26 '14 at 17:32
• 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)? – Chirac Oct 26 '14 at 17:35
• 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. – K7PEH Oct 26 '14 at 18:02
• 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. – TZDZ Nov 4 '14 at 14:21