Question

A bubble of 1 cm radius is rising at a steady rate of 0.5. cm s^-1 through a liquid of density 0.8 g cm^-3. Calculate the coefficient of viscosity of the liquid. Neglect the density of air.

Answer 1

Radius of the air bubble,

r = 1 cm

Density of air, ρ = 0

Density of liquid (viscous medium)

σ = 0.8 cm^-3

Terminal velocity of air bubble,

v = -0.5 cm s^-1

(The velocity has taken negative value, for the bubbles is moving upwards).

Now,

v = {2(ρ - σ)r²g}/{9η}

η = {2(R - σ)r²g}/{9} = {2(0 - 0.08) x (1)² x 890}/{9 x (-0.5)}

= {2 x 0.08 x (1)² x 890}/{9 x 0.5} 

= 348.44 Poise