1.

Two plane parallel conducting plates `1.5xx10^(-2)m` apart are held horizontal one above the other in air. The upper plate is maintained at a positive potential of`1.5kV` while the other plate is earthed. Calculate the number of electrons which must be attached to a small oil drop of mass `4.8xx10^(-15)kg` between the plates of move the drop with constant speed. Neglect the density and viscosity of air.

Answer» Correct Answer - 3
`F=qE=-"ne" V/d=mg`
`n=(mgd)/(eV)=(4.8xx10^(-15)xx10xx1.5xx10^(-2))/(1.6xx10^(-19)xx1500)=3`


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