As shown in the figure the voltmeter reads 2 V across 5 Ω resistor. The resistance of the voltmeter is _____ Ω

Step-by-step solution

Let the resistance of the voltmeter be R   Ω . The voltmeter is in parallel with the 5   Ω . So the total resistance in the circuit is 5 R 5 + R + 2   Ω Applying Ohm's law in the whole circuit, V = I R , I = 3   2 + 5 R 5 + R   A It is given that the potential difference across 5   Ω is 2   V . Thus, by Ohm's law, 3 2 + 5 R 5 + R × 5 R R + 5 = 2 ⇒ 15 + 3 R 10 + 7 R × 5 R 5 + R = 2 ⇒ 15 R = 20 + 14 R ⇒ R = 20   Ω