- #1

Jenkz

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## Homework Statement

Find the terminal velocity of an oil drop with radius 1x10^-6 m at 20 degress under zero field conditions. How long would it take to fall 5mm (range of microscope graticule)?

## Homework Equations

Terminal velocity; Weight = Drag

Weight = mg

Assuming Stokes law holds; Drag = 6(pi)rηv

v - terminal velocity

r - radius of droplet

η -viscosity of air, 1.832×10–5 Pa s (at 20 degrees)

Mass, m = (4/3) pi (r^3) [tex]\rho[/tex]

[tex]\rho[/tex] = Density of oil, 874 kgm^-3 (at 20 degrees)

time= distance/ velocity

## The Attempt at a Solution

Mass = 3.66 x 10^-15 Kg

v = (mg) / (6(pi)rη) = 1.04 x10^-4 ms^-1

time = 48s

The velocity seems too small, and the time taken is definitely too long. Please help?