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Home » A metre long narrow bore held horizontally (and closed at one end) contains a long mercury thread, which traps a 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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