Physics Electrostatics Potential & Capacitance Electric Field and Potential,Defference,Energy and Dipole Single Correct MCQ
Published on: September 12, 2026

An oil drop having charge $2e$ is kept stationary between two parallel horizontal plates 2.0 cm apart when a potential difference of 12000 volts is applied between them. If the density of oil is 900 kg/m 3 , the radius of the drop will be

A
$2.0 \times 10^{-6} \, m$
B
$1.7 \times 10^{-8} \, m$
C
$1.4 \times 10^{-6} \, m$
D
$1.1 \times 10^{-6} \, m$

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Text Solution

Verified by Experts
The correct answer is:
B

In equilibrium QE = mg

⇒ ⇒ $Q \cdot \frac{v}{d} = mg = \left(\frac{4}{3} \pi r^{3} \rho \right) g$

⇒ ⇒ $2 \times 1.6 \times 10^{-19} \times \frac{12000}{2 \times 10^{-2}} = \frac{4}{3} \pi r^{3} \times 900 \times 10^{-3}$

⇒ ⇒ r = 1.7 × × 10 –6 m

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