Increasing parallel resistance shifts voltage division in potential divider

Steps:

• Potential divider voltage splits proportionally to resistances: V_lower = V_total * (R_lower / (R_upper + R_lower)).
• Variable R parallels fixed lower resistor, so effective R_lower = (R_fixed * R) / (R_fixed + R).
• Increasing R raises effective R_lower toward R_fixed, increasing its share of total resistance.
• Thus, voltage across lower (V2) rises while across upper (V1) falls.

Why B is correct:

• Effective lower resistance increase causes larger voltage drop across it by voltage division formula.

Why the others are wrong:

• A: V2 actually increases, not decreases.
• C: V1 decreases while V2 increases, opposite of this.
• D: Fixed total voltage means shares cannot both increase.

Final answer: B