Question

Mercury has an angle of contact equal to 140° with soda lime glass. A narrow tube of radius 1.00 mm made of this glass is dipped in a trough containing mercury. By what amount does the mercury dip down in the tube relative to the liquid surface outside ? Surface tension of mercury at the temperature of the experiment is 0.465 N m¯¹Density of mercury = 13.6 × 103 kg m¯³

Answer 1

Given that

r=

Radius of the tube =1.00 mm= 10 −3  m

σ=

Surface tension of the mercury =0.465  Nm -1

ρ=

Density of the mercury =13.6× 10 3   kgm -3

θ=

Angle of contact = 140 ∘

Height at which mercury level changes is given by,

h= 2σcosθ rρg

Substitute the values.

h= 2×0.465×cos 140 ∘ 10 −3 ×13.6× 10 3 ×9.8 h=−5.34× 10 −3  m h=−5.34 mm

Negative sign shows that the mercury level is depressed into the tube relative to liquid surface outside the tube.