A galvanometer of resistance 50 Ω is connected to a 3 V cell with 2950 Ω in series and gives 30 divisions deflection. Find the NEW external series resistance for 20 divisions deflection.
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A galvanometer of resistance 50 Ω is connected to a 3 V cell with 2950 Ω in series and gives 30 divisions deflection. Find the NEW external series resistance for 20 divisions deflection.

G1 Physics · Accepted Answer

Step 1: The instrument has G=50Ω and 2950Ω in series, so initial total resistance is 3000Ω. Step 2: Full scale at 3V is I(g)=3/3000=1mA for 30 divisions; use proportionality θ∝I to find current needed for requested divisions. Step 3: Required series resistance follows R(total)=3V/I(new) and R(extra)=R(total)−G; the source's value is 4450Ω (D). Check the printed target divisions. Final answer: (D) 4450 Ω.