Limiting current to prevent cell polarization Steps: - In a potentiometer, the emf ε of the new source is measured by null deflection on the galvanometer when the potential drop along length l equals ε, so ε = k l, where k is the potential gradient. - Precision suffers if the new source polarizes due to current flow during adjustments, altering the true emf. - Adding resistance in series with the new source limits this current (i ≈ δV / R_series for small unbalance δV), minimizing polarization for a stable, accurate null point. - A 10 Ω resistor provides significant current limiting, as it matches the wire's 10 Ω resistance, unlike smaller values. Why B is correct: - Adding 10 Ω in series with the new source limits adjustment currents effectively (per Ohm's law, i = δV / (R_g + 10 Ω + r_wire)), preventing polarization and ensuring the measured emf reflects the true open-circuit value. Why the others are wrong: - A: Adding 0.1 Ω to E slightly reduces k (from 1 V/m to ~0.99 V/m) but does not …