Question

In the following figure ammeter and voltmeter reads 2 amp and 120 volt respectively. Resistance of voltmeter is

• A. 100 Ω
• B. 200 Ω
• C. 300 Ω
• D. 400 Ω

Answer 1

Answer: (C)

300 Ω

Answer 2

Let resistance of voltmeter be R_V. Equivalent resistance between X and Y is $R _ { X Y } = \frac { 75 R _ { V } } { 75 + R _ { V } }$

Reading of voltmeter = potential difference across X and Y = 120 = i × R_XY = $2 \times \frac { 75 R _ { V } } { 75 + R _ { V } }$ ⇒ R_V = 300Ω