An 80W galvanometer deflects full-scale for a potential of 20 mV. A voltmeter deflecting full-scale of 5 V is to be made using this galvanometer. We must connect

The current through the galvanometer producing full-scale deflection isI=VR=20×10−380=2.5×10−4ATo convert the galvanometer into a voltmeter, a high resistance is connected in series with the galvanometer. Therefore, 5 V = (2.5 × 10-4)(R + 80)             or        R = 19.92 kΩ