Question

The capillaries shown in figure (14-E4) have inner radii 0.5 mm, 1.0 mm and 1.5 mm respectively. The liquid in the beaker is water. Find the heights of water level in the capillaries. The surface tension of water is 7.5 x 10 ^-2 N/m.

Answer 1

The rise in a capillary = 2S.cosθ/rρg 

Here S = 7.5x10⁻² N/m, ρ = 1000 kg/m², Let g = 10 m/s², 

For water θ = 0°.  

Hence for A, r = 0.5 mm =0.0005 m 

Rise = 2* 7.5x10⁻²*cos0°/(0.0005*1000*10) 

=15/500 m 

=3/100 m 

=3 cm  

For B, r = 1.0 mm =0.001 m 

Rise = 2* 7.5x10⁻²*cos0°/(0.001*1000*10) =

15/1000 m 

=15*100/1000 cm 

=1.5 cm  

For C, r = 1.5 mm =0.0015 m 

Rise = 2* 7.5x10⁻²*cos0°/(0.0015*1000*10) 

=15/1500 m 

=1/100 m 

=1.0 cm

Answer 2

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