Question:
A metre long narrow bore held horizontally (and closed at one end) contains a 76 cm long mercury thread, which traps a 15 cm column of air. What happens if the tube is held vertically with the open end at the bottom ?
Answer:
When the tube is held horizontally,
length of mercury thread = 76 cm
length of air = 15 cm.
Blank space at the open end = 100 - 76 - 15 = 9cm
Pressure of air closed in the tube is atmospheric pressure, P1 = 76cm V, = 15cm3,
When tube is held vertically. Let the total length of air be = 2.15 + 9 + h and length of mercury column = 76 - h
P2 - Pressure of air 76 - (76 - h) = h cm of Hg
P1 V1 = P2 V2 = 76× 15 = h x (24 - h), h = 23.8 and 47.8 cm,
When tube is held vertically,
Let the tube length of air be = 2.15 + a + h and length of mercury column = 76 - h
P2 - Pressure of air 76 - (76 - h) = h cm of Hg
V2 = 29 + h cm3
As temperature is constant ,
P1 V1 = P2 V2 = P1 V1 = P2 V2 = 76× 15 = h x (24 - h)
h = 23.8 = 24 cm, length of mercury column = 52 cm.
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