Force balance in electric field

Steps:

• Uniform electric field between plates: E = V/d.
• Gravitational force on drop: mg downward.
• Electric force on drop: qE upward (to hold stationary).
• Net force zero: qE = mg, so q/m = g/E = gd/V.

Why A is correct:

• Force balance equation directly yields q/m = gd/V from q(V/d) = mg.

Why the others are wrong:

• B: Inverts the ratio, giving E/g instead of g/E.
• C: Multiplies g by E, implying forces add rather than balance.
• D: Same as C, gE from incorrect force relation.

Final answer: A