Question

A $20$ cm long capillary tube is dipped in water. The water rises upto $8$ cm. If the entire arrangement is put in a freely falling elevator, the length of the water column in the capillary tube will be:

• A. Zero
• B. $8$ cm
• C. $4$ cm
• D. $20$ cm

Answer 1

Answer: (D)

$20$ cm

The level of liquid in a thin capillary is given by the formula:

$h=\frac{2\gamma cos\theta }{\rho gr}$

So when the arrangement is put in a freely falling elevator, $g=0$ .

Thus the surface tension has no opposing force and the water level rises to maximum height possible in the capillary.

Once it reaches the other end, it cannot go further up. Thus the length of water column = $20cm$.