Question

A glass capillary tube of inner diameter 0.28 mm
is lowered vertically into water in a vessel. The
pressure to be applied on the water in the capillary
tube so that water level in the tube
is same as that in the vessel is (surface
tension of water = 0.07 N/m and atmospheric
pressure = 105 N/m2).
(1) 103
(2) 99 ~ 103
(3) 100 x 103
(4) 101 x 103​

Answer 1

The pressure to be applied on the water in the capillary  tube so that water level in the tube  is same as that in the vessel is 101 × 10³ Pascal.

Given-

• Inner diameter of glass capillary tube = 0.28 mm
• Surface tension of water = 0.07 N/m
• Atmospheric pressure = 10⁵ N/m²

To cancel out excess pressure we know that

P₀ + P excess = P₀ + 2T/R

Here 2T/R is the excess pressure.

So, P = 10⁵ + 2×0.07/0.14 ×10⁻³

P = 10⁵ + 10³

P = 10⁵ + 0.01 × 10⁵

P = 1.01 × 10⁵

P = 101 × 10³ Pa