Question

When one end of the capillary is dipped in water, the height of water column is 'h'. The upward force of 105 dyne due to surface tension is balanced by the force due to the weight of water column. The inner circumference of capillary is ______.

(Surface tension of water = 7 × 10^-2 N/m)

Options

• 1.5 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 105 dyne due to surface tension is balanced by the force due to the weight of water column. The inner circumference of capillary is 1.5 cm.

(Surface tension of water = 7 × 10^-2 N/m)

Explanation:

According to question,

force F = 150 dyne 105 × 10^-5  N and

Surface tension T = 7 × 10^-2 N/m ·

∵ Circumference of the capillary × surface tension = upward force

∴ 2πrT = F

or, 2πT = `"F"/"T"`

= `(105xx10^-5)/(7xx10^-2)`

= 15 × 10^-3 m 

= 1.5 × 10^-2 cm

= 1.5 cm