Mercury has an angle of contact equal to `140^(0)` with soda lime glass. A narrow tube of radius 1 mm made of the glass is dipped in a trough containing mercury. The surface tension of mercury at the temperature of the experiment is `0.465 N m^(-1)`. The distance by which the mercury dip down in the tube relative to the mercury surface outside is ( Density of mercury = `13.6 xx 10^(3) kg m^(-3)` )

Explanation

`theta = 140^(@) , r = 1 xx 10^(-3) m`
`sigma = 0.465 Nm^(-1) , rho = 13.6 xx 10^(3) kg m^(-3)`
Capillary descent `= h = ( 2 sigma cos theta )/( r rho g )`
` = ( 2 xx 0.465 cos 140^(@))/( 1 xx 10^(-3) xx 13.6 xx 10^(3) xx9.8) = ( 0.930 ( - 0.7660))/( 13.6 xx 9.8 ) = - 5.345 xx 10^(-3) m`
Negative sign shows that mercury gets depressed.