Question

The resistance of a voltmeter is 180 ohm. When there is
5 V potential difference across its ends, it gives full-
scale deflection. What resistance should be connected
in series to obtain a full-scale deflection at 25 V?​

Answer 1

Answer:

If current is I and required resistance be R then we have

5 = 180I

and, 25 = (180+R)I

So, 5/180 = 25/(180+R)

=> R = 25×36 - 180 = 720ohm