Question

The resistance of an ideal voltmeter is
(A). Zero
(B). Infinity
(C). $1000\Omega$
(D). $10000\Omega$

Answer 1

Voltmeter is a device which is used to measure the potential difference between two points. It is connected in parallel between the points the potential is to be calculated. Since the potential is directly proportional to the resistance, the more the
resistance, the more accurately potential is calculated.

Complete answer:
A voltmeter is a device which is used to measure the potential difference between two points in a circuit and almost negligible current passes through it.
Potential difference between two points is the work done to move a charge between those two points in a circuit. Its SI unit is volt ($V$). Current in the circuit flows from a point of higher potential to a point of lower potential.
The voltmeter is connected in parallel between the points potential is to be measured.
According to the Ohm’s law,
$R=\dfrac{V}{I}$
Here, $R$ is the resistance
$V$ is the potential difference between two points
$I$ is the current
From the above equation we can see that,
$V\propto R$
Therefore as resistance increases, the potential drop also increases. So, to get the absolute potential drop between two points the resistance should be maximum. Therefore, resistance should be infinity.
Therefore, the resistance of an ideal voltmeter is infinity.

Hence, the correct option is (B).

Note:
A galvanometer can be converted into a voltmeter by connecting a high resistance in series with it. A voltmeter is connected in parallel while an ammeter is connected in series. For all devices connected in parallel between two points, the potential drop on all devices will be the same. The deflection caused per unit potential drop is called the sensitivity of voltmeter.