Current Electricity Part 4

Concept:A voltmeter connected in parallel with a resistor changes the effective resistance of that branch, affecting the circuit's current and voltage distribution.Explanation:The voltmeter resistance $R_V = 400\ \Omega$ is in parallel with one resistor $R_1 = 100\ \Omega$.The equivalent resistance of the parallel combination is $R_{1V} = \frac{R_1 R_V}{R_1 + R_V} = \frac{100 \times 400}{100 + 400} = 80\ \Omega$.This combination is in series with the other resistor $R_2 = 100\ \Omega$.Total circuit resistance: $R_{\text{total}} = 80 + 100 = 180\ \Omega$.Using Ohm's law for the whole circuit: $I = \frac{V}{R_{\text{total}}} = \frac{9}{180} = 0.05\ \text{A}$.This current flows through both the series resistor and the parallel combination.The voltmeter measures the voltage across the parallel combination.Hence, voltmeter reading: $V_{\text{reading}} = I \times R_{1V} = 0.05 \times 80 = 4\ \text{V}$.Answer:$4\ \text{V}$ (Option C).