A galvanometer of coil resistance 100 Ω gives full-scale deflection at 30 mA. To convert it into a voltmeter with full-scale range 30 V, find the resistance to add in series.
Options

Question

A galvanometer of coil resistance 100 Ω gives full-scale deflection at 30 mA. To convert it into a voltmeter with full-scale range 30 V, find the resistance to add in series.

G1 Physics · Accepted Answer

Step 1: To convert a galvanometer of resistance G=100Ω and full-scale current I(g)=30mA into V=30V voltmeter, add resistance in series. Step 2: At full scale: V=I(g)(G+R(series)). Solve R(series)=V/I(g)−G. Step 3: R(series)=30/0.030−100=1000−100=900Ω. Answer A. Final answer: (A) 900 Ω.