PHYS208 Fundamentals of Physics II

Makeup Quiz -- Galvanometers

[circuit] 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.


Solution:

The voltage across the galvanometer went deflected full-scale is (25 ohm)(1 mA) = 25 mV.

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.


"http://www.physics.udel.edu/~watson/phys208/quiz11soln.html"
Last updated Nov. 28, 1997. Last updated Nov. 28, 1997.
Copyright George Watson, Univ. of Delaware, 1997.