An oil drop of radius $ 1 \mu \mathrm{~m} $ is held stationary under a constant electric field of $ 3.65 \times 10^{4} \mathrm{~N} / \mathrm{C} $ due to some excess electrons presence on it. If the density of oil drop is $ 1.26 \mathrm{~g} / \mathrm{cm}^{3} $, then number of excess electrons on the oil drop approximately are [Take, $ g=10 \mathrm{~ms}^{-2} $ ]

The potential of a large liquid drop when eight liquid drops are combined is 20 V , then the potential of each single drop was

A dust particle of mass $ 4 \times 10^{-12} \mathrm{mg} $ in suspended in air under the influence of an electric field of $ 50 \mathrm{~N} / \mathrm{C} $ directed vertically upwards. How many electrons were removed from the neutral dust particle? [Take, $ g=10 \mathrm{~m} / \mathrm{s} $ $ { }^{2} $ ]

Electric field at point $ (30,30,0) $ due to a charge of $ 0.008 \mu \mathrm{C} $ placed at origin will be, (coordinates are in cm )