Question

The force of $2000$ dyne is required to move a flat glass plate of surface area $10c{m}^2$ with a velocity of $1cm/s$ over a surface of glycerine $1mm$ thick. The coefficient of viscosity of glycerine is

• A. $0.2poise$
• B. $0poise$
• C. $20poise$
• D. $20.5poise$

Answer 1

Answer: (C)

$20poise$

Given:

Surface area of glass plate over glycerine $=10c{m}^2$

The velocity of the plate $=1cm/s$

The force applied on plate $=2000dyne$

Thickness of glycerine $=1mm$.

To find: The coefficient of viscosity of glycerine.

The force applied on the plate is given by:

$F=\eta A\frac{dv}{dx}$

$dv$ is the small velocity of plate and $dx$ is the thickness.

$2000=\eta \times 10c{m}^2\times \frac{1cm/s}{10mm}$

$2000=\eta \times 10\times 10s^{-1}$

$\eta =\frac{2000}{100}dyne-s/c{m}^2$

$\eta =20dyne-s/c{m}^2$ or $20$ poise.