A galvanometer needs 6.0V at full scale deflection and is graded according to its resistance per volt at full scale deflection as . How will you convert it into a voltmeter that needs 30V at full scale deflection?
171428
174682
17328
48792
Hence, resistance per volt =
It means for 1 volt potential difference, the resistance of galvanometer is .
So current for full scale deflection
In order to convert it into a voltmeter of range 0 to 30V, let a resistance R be connected in series with it. Then on applying an extra potential difference = 30V-6V = 24V
The current through it for full scale deflection is again
i.e.
Thus, to convert a given galvanometer (of range 0 to 6V) into a voltmeter (of range 0 to 30V) a resistance of 171428 should be connected in series.