A galvanometer having 20 divisions has a resistance of 50 . A deflection of one division in this galvanometer needs a current of 0.2 mA . What should be the resistance that needs to be connected to this galvanometer to convert it to a voltmeter of range (0-20) volts?

Step-by-step solution

The full scale deflection current I_g of the galvanometer is calculated by multiplying the number of divisions by the current per division. I_g = 20 0.2 mA = 20 0.2 10⁻³ A = 4 10⁻³ A = 0.004 A . The resistance of the galvanometer is G = 50 . To convert a galvanometer into a voltmeter of range V , a high resistance R must be connected in series with the galvanometer. The formula for the series resistance is V = I_g(G + R) . Substituting the given values, 20 = 0.004(50 + R) . Dividing both sides by 0.004 , we get 20