Question

35. A 20 cm column of air is trapped by a
column of Hg 15 cm long in a capillary tube
of uniform bore when the tube is held
horizontally in a room where the
atmospheric pressure is 75 cm of mercury.
The length of the air column, when the tube
is held vertically with open end up will be
Trapped air
Mercury column
15 cm
20 cm
1) 20 cm
3) 16.7 cm
2) 25 cm
4) 18.9 cm
​

Answer 1

Answer:

25 cm

hope will help you

Answer 2

Answer:

The length of the air column, when the tube is held vertically with open end up will be 16.7 cm.

Explanation:

At the horizontal position of tube, air pressure is 75 cmHg. If the tube is now held in different given positions at the same temperature, the length of air column will vary. Applying Boyle's law, we have,

                                  $P_1V_1 = P_2V_2$

                             →  $P_1 l_1 A =P_2 l_2A$

                            →  $P_1 l_1 =P_2 l_2$ ................................................(i)

Now when the tube is held vertically with open end up,

air pressure ($P_2$) = 75 cmHg + 15 cmHg

                           = 90 cmHg

From equation (i),

                          $l_2 = \frac{P_1l_1}{P_2}$

                               $= \frac{75 * 20}{90}$

                               = $\frac{150}{9}$  = 16.7 cm  [Option(3)]

∴ The length of the air column, when the tube is held vertically with    open end up will be 16.7 cm.