In Millikan's oil drop experiment, what is viscous force acting on an uncharged drop of radius 2.0 × 10⁻⁵ m and density 1.2 × 10³ kg m⁻³? Take viscosity of liquid = 1.8 × 10⁻⁵ N s m⁻². (Neglect buoyancy due to air)
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Question

In Millikan's oil drop experiment, what is viscous force acting on an uncharged drop of radius 2.0 × 10⁻⁵ m and density 1.2 × 10³ kg m⁻³? Take viscosity of liquid = 1.8 × 10⁻⁵ N s m⁻². (Neglect buoyancy due to air)

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G1 Physics · Accepted Answer

Step 1: At terminal speed in Millikan's experiment, Stokes drag balances weight: F=6πηrv=mg=(4/3)πr³ρg when buoyancy is neglected. Step 2: Using the given r and ρ gives about 3.9×10⁻10 N. Final answer: B.