In this circuit there is a current of 360 mA through the lamp and 2.52 V across it. Given a galvanometer with 25 ohm resistance and a current for full-scale deflection of 1.0 mA, design an ammeter and voltmeter to confirm the stated circuit values.
a) Design an ammeter with 500 mA full-scale deflection.
b) Design a voltmeter with 5.0 V full-scale deflection.
a) For the ammeter, we add a resistance in parallel to shunt 499 mA of the current around the galvanometer, at a voltage difference of 25 mV. That resistance has a value (25 mV)/(499 mA) = 0.050 ohm.
b) For the voltmeter, we add a resistance in series to drop all but 25 mV of the 5.0 V across the two, while the current is 1.0 mA. That resistance has a value (4.975 V)/(1.0 mA) = 4.98 k-ohm.