Properties of Matter 2 Question 23

23. A column of mercury of length 10cm is contained in the middle of a horizontal tube of length 1m which is closed at both the ends. The two equal lengths contain air at standard atmospheric pressure of 0.76m of mercury. The tube is now turned to vertical position. By what distance will the column of mercury be displaced? Assume temperature to be constant.

(1978)

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Answer:

Correct Answer: 23. 2.95 cm

Solution:

  1. Let area of cross-section of the tube be A.

(b)

Applying p1V1=p2V2 in A and B we have,

p0(45)(A)=p1(45x)A or 76×45=p1(45x)(i)p0(45)(A)=p2(45+x)A76×45=p2(45+x)(ii)

From Eqs. (i) and (ii), we get

(p1p2)=76×45(145x145+x)

From figure (b),

(p1p2)A= Weight of 10cm of Hg column

or p1p2= Pressure equivalent to 10cm of Hg column

76×45(145x145+x)=10

Solving this equation, we get

x=2.95cm



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