The Total solution for NCERT class 6-12
In Millikan’s oil drop experiment, what is the terminal speed ofan uncharged drop of radius 2.0 × 10–5 m and density 1.2 × 103 kgm–3? Take the viscosity of air at the temperature of the experimentto be 1.8 × 10–5 Pa s. How much is the viscous force on thedrop at that speed? Neglect buoyancy of the drop due to air.
Terminal speed = 5.8 cm/s; Viscous force = 3.9 × 10–10 N
Radius of the given uncharged drop, r = 2.0 × 10–5 m
Density of the uncharged drop, ρ = 1.2 × 103 kgm–3
Viscosity of air,
Density of air can be taken as zero inorder to neglect buoyancy of air.
Acceleration due to gravity, g = 9.8 m/s2
Hence, the terminal speed of the drop is 5.8 cm s–1.
The viscous force on the drop is given by:
Hence, the viscous force on the drop is 3.9 × 10–10 N.