Question

why voltmeter is always connected in parallel ​

Answer 1

Voltmeter is used to calculate the potential difference of a circuit and we know that the objects connected in parallel combination experience the same potential difference. so; to avoid faulty readings it is connected parallely to the circuit whose potential difference is to be measured.

Answer 2

Ammeter:-

An ammeter is just a converted Galvanometer and measures the current flowing through the circuit by showing proportional deflection. An ammeter is formed by connecting a Galvanometer with a low resistance in parallel.

$\bigstar$So the ammeter is connected in series with the circuit elements and the measures the current flow in a circuit.

Voltmeter:-

A Voltmeter is also a converted Galvanometer which measures the amount of Voltage (or) in other words the potential difference accross two points in a circuit. A voltmeter is formed by connecting a Galvanometer in series with a high resistance.

$\bigstar$So the Voltmeter is attached in parallel in a circuit and measures the voltage in a circuit

And if this is not maintained then there is a high chance for the ammeter to get damaged due to low resistance.