Question

Q: a tube full of mercury placed upside down in a dish of mercury. Initially a small piece of glass closes the open end of the tube. (a) The piece of glass is removed and the level of mercury in the inverted tube falls, as shown in the figure. (i) Explain why the level of mercury in the tube falls.

Answer 1

Using isothermal process conditions

We have P

1

​

V

1

​

=P

2

​

V

2

​

Thus

8AP

0

​

=PAx(A is the cross-sectional area of the tube and P is the pressure in the tube when it is raised)

Thus P=

x

8P

o

​

​

Thus equating the pressure at points 1 and 2 we get

x

8P

o

​

​

+ρ

m

​

g(54−x)=ρ

m

​

g(76)

or

x

8

​

ρ

m

​

g(76)+ρ

m

​

g(54−x)=ρ

m

​

g(76)

or

x

8

​

+

76

54−x

​

=1

Thus x=16 cm