Problem 29 - A Complete Resource Book in Physics for JEE Main

Question

Which of the following has the maximum resistance? (A) Voltmeter (B) Millivoltmeter (C) Ammeter (D) Milliammeter

Step-by-Step Solution

Answer

The instrument with the maximum resistance is the \(Voltmeter\). Therefore, the answer is \((A)\) Voltmeter.

Step 1: Understanding the Instruments and their Resistances

Each of these instruments has a certain resistance associated with it based on its design and the role it plays in a circuit. The resistance is high for a device connected in parallel (like a Voltmeter or Millivoltmeter) and low for an instrument installed in series (like an Ammeter or Milliammeter). High resistance in a parallel-connected device ensures it doesn't draw much current, which could interfere with the operation of the rest of the circuit. Series-connected devices have low resistance, again to avoid disturbing the circuit, but this time by not presenting a significant resistance to the current flow.

Step 2: Comparing the Resistances

Between Voltmeter and Millivoltmeter, the one connected across the larger potential difference, Voltmeter, will have more resistance. This is to ensure that the device itself doesn't draw too much current while trying to measure the voltage. Between Ammeter and Milliammeter, both are used to measure current and are connected in series, and because of this, they would ideally have near-zero resistance. But in practical reality, Ammeter will have a small resistance associated, but it would be less than Milliammeter which is used for smaller current measurements.

Step 3: Identifying Maximum Resistance

Given that the resistance rankings based on their connections and roles in the circuit, from high to low, are: Voltmeter, Millivoltmeter, Milliammeter and Ammeter. The instrument with the maximum resistance is the Voltmeter. So the answer to the exercise is (A) Voltmeter.