Solution for Question 9
1. Analyze the Circuit Structure
The circuit is a ladder network. The Voltmeter (V) measures the voltage across a parallel branch near the end. The Rheostat is located in the final branch, and the Ammeter (A) measures the current flowing through this rheostat.
2. Effect of Increasing Rheostat Resistance
When the resistance of the rheostat increases, the resistance of that specific branch increases. Since this branch is part of the load of the network, the total equivalent resistance of the entire circuit increases.
3. Analyze Voltmeter Reading
The network to the left of the voltmeter can be treated as a voltage source with some internal resistance (Thevenin equivalent). The voltmeter measures the voltage across the load (the rheostat branch). As the load resistance increases, it takes a larger share of the potential drop from the source (Voltage Divider Rule). Therefore, the Voltmeter reading increases.
4. Analyze Ammeter Reading
The current through the ammeter is given by I = V / Rbranch. Even though the voltage V increases slightly, the resistance Rbranch increases directly. In a circuit driven by a source with internal resistance (the rest of the network), increasing the load resistance always results in a decrease in the load current. Therefore, the Ammeter reading decreases.
Correct Option: (c) Voltmeter reading will increase and ammeter reading will decrease.