Why the voltmeter needs to be connected in parallel with resistor?
Because a voltmeter measures a potential difference, voltage. It compares the voltage on one probe with the voltage on the other and gives the difference. Since they are annotated in parallel, they must have a high resistance so that the operation of the circuit is not affected.
The voltmeter is connected in parallel to the circuit elements since it is used to measure the device voltage. This is important because elements in series have the same potential difference.
When connected in series, it changes the value of the potential difference, which minimizes the current in the circuit as it has a very large resistance and you get erroneous readings.
You will probably ask about the connection when reading the voltage drop. Yes, the measuring device is technically arranged parallel to the resistor, but it is more often said that the voltage probes are arranged above the resistor.
How could you measure the voltage drop differently than at two points – in a circuit or on a component (e.g. a resistor)? You measure the voltage drop (or in the case of a battery or a power supply unit the potential) from point A to point B. By bridging the measuring device from A to B, you of course connect it in parallel, but since it is not permanent connection we simply say “between” A and B “or” via the (circuit) (component) “.
If a voltmeter is connected in series with a resistor, there is a risk that the measuring device will be burned out (almost certainly) and no meaningful indication will be given. Only one ammeter would be connected in series to make a measurement.
In addition, an ohmmeter is also arranged in parallel or across a circuit or device. But not when electricity is flowing.