Why is voltmeter connected in parallel and ammeter connected in series in a circuit?

Answer 1

An ideal voltmeter has infinite impedance(resistance). If you were to break the circuit and put it in series and try to make a measurement, it is easy to see that the circuit would act completely differently and your measurement would be wrong. An ideal ammeter is always connected in series because it has 0 resistance, so all of the current would flow through it, and not through the wire that you are trying to measure the current of.

A better answer though is to think about what you are trying to measure. When you say something is 3 Volts, that is a difference between the voltages at two different points. If you want to see what the voltage drop across a resistor is, for example, you need to put one probe of the voltmeter on one side of the resistor and the other probe on the other side of the resistor. That setup is simply called being in parallel.
Voltage is potential difference between two points, hence measured across or in parallel, where as current is measured in series since current flows (*)

Answer 2

A voltmeter measures voltage change between two points in a circuit which generally is different, depending on what two points you chose. So to measure the voltage change between two points in a circuit you have to place the meter probes at these two points, without removing the portion of circuit between the probes (or else you change the circuit). This then, by definition, places the voltmeter in parallel with the section of circuit between the probes. When you place the meter probes at the two points you want to measure, a tiny portion of the current in the circuit will now go thru the meter and give you a reading. The best voltmeters give a reading by using the least amount of the original current because you don't want to significantly alter anything about the circuit. This is accomplished by making the voltmeter a very high resistance instrument. So when the current splits into the meter the high resistance allows only a tiny amount of original current to split into the meter.

Notice the difference in an ammeter. An ammeter measures the current (flow of charge) in a circuit which is the same everywhere in a length of circuit. In this case the meter is placed anywhere convienient in line with the circuit Since ammeters are in line with the original circuit it is important that they not effect the current being measured. So ammeters are very low resistance instruments since any resistance placed in line will reduce the current.

Answer 3

A voltmeter measures the potential difference between the two points it is connected to.If connected in series,you effectively break the circuit since the voltmeter has a very high impedance.

Answer 4

Because it should not be connected in series