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A metre long narrow bore held horizontally (and closed at one end) contains a $76 \mathrm{~cm}$ long mercury thread, which traps a $15 \mathrm{~cm}$ column of air. What happens if the tube is held vertically with the open end at the bottom?
A metre long narrow bore held horizontally (and closed at one end) contains a $76 \mathrm{~cm}$ long mercury thread, which traps a $15 \mathrm{~cm}$ column of air. What happens if the tube is held vertically with the open end at the bottom?
CBSE | Class 11 | Kinetic Theory | NCERT | Physics
A metre long narrow bore held horizontally (and closed at one end) contains a $76 \mathrm{~cm}$ long mercury thread, which traps a $15 \mathrm{~cm}$ column of air. What happens if the tube is held vertically with the open end at the bottom?

Length of the narrow bore is given as $L=1 \mathrm{~m}=100 \mathrm{~cm}$

Length of the mercury thread is given as $\mid=76 \mathrm{~cm}$

Length of the air column between mercury and the closed end, $l a=15 \mathrm{~cm}$ air space is:

$=100-(76+15)$

So,

The total length of the air column will be $=15+9=24 \mathrm{~cm}$

Let h cm of mercury flow out as a result of atmospheric pressure

So we have,

Length of the air column in the bore will be $=24+\mathrm{h}$ cm

And,

Temperature remains constant throughout the process

Therefore,

On substituting, we get,

On solving further, we get,

$=23.8 \mathrm{~cm}$ or $-47.8 \mathrm{~cm}$

Since height cannot be negative. Hence, $23.8 \mathrm{~cm}$ of mercury will flow out from the bore

Length of the air column $=24+23.8=47.8 \mathrm{~cm}$

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