The voltmeter has range 10 V and its internal resistance is 50 . To increase the range of voltmeter to 15 V , the resistance which is to be connected is

Step-by-step solution

To extend the voltmeter range to 15 V, a series resistance is required. The full-scale deflection current remains I_g = V / R_v = 10 V / 50 = 0.2 A . For the new range V' = I_g (R_v + R_s) , so 15 = 0.2(50 + R_s) . Solving gives R_s = 15 / 0.2 - 50 = 75 - 50 = 25 . A 25 series resistance corresponds to option D .