In Millikan's oil drop experiment, what is viscous force acting on an uncharged drop of radius $2.0 \times 10^{-5}\, {m}$ and density $1.2 \times 10^{3} \,{kgm}^{-3}$ ? Take viscosity of liquid $=1.8 \times 10^{-5}\, {Nsm}^{-2} .$ (Neglect buoyancy due to air).
JEE MAIN 2021, Medium
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Viscous force $=$ Weight
$=\rho \times\left(\frac{4}{3} \pi^{3}\right) \,g$
$=3.9 \times 10^{-10}$
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