Two large circular discs separated by a distance of \( 0.01 \mathrm{~m} \) are connected to a battery via a switch as shown in the figure. Charged oil drops of density \( 900 \mathrm{~kg} \mathrm{~m}^{-3} \) are released through a tiny hole at the center of the top disc. Once some oil drops achieve terminal velocity, the switch is closed to apply a voltage of \( 200 \mathrm{~V} \) across the discs. As a result, an oil drop of radius \( 8 \times 10^{-7} \mathrm{~m} \) stops moving vertically and floats between the discs. The number of electrons present in this oil drop is (Neglect the buoyancy force, take acceleration due to gravity \( =10 \mathrm{~ms}^{-2} \) and charge on an electron \( (e)=1.6 \times 10^{-19} \mathrm{C} \) )
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