Question

When one end of the capillary is dipped in water, the height of water column is 'h'. The upward force of 119 dyne due to surface tension is balanced by the force due to the weight of water column. The inner circumference of the capillary is (Surface tension of water= 7 x 10^-2 N/m) ____________.

Options

• 1.7 cm

• 2 cm

• 2.5 cm

• 3 cm

Answer 1

When one end of the capillary is dipped in water, the height of water column is 'h'. The upward force of 119 dyne due to surface tension is balanced by the force due to the weight of water column. The inner circumference of the capillary is 1.7 cm.

Explanation:

F = 119 dyne = 119 x 10^-5 N,

T = 7 x 10^-2 N/m

Now the force due to surface tension on the circular cross-section of capillary with inner radius r will be,

`"F" = 2 pi"rT"`

`therefore 2pi"r" = "F"/"T"`

` = (119 xx 10^-5)/(7 xx 10^-2)`

`= 17 xx 10^-3  "m"`

`= 1.7  "cm"`