Jawaban:

(a) For figure (a)

Atmospheric pressure, P0= 76 cm of Hg

Difference between the levels of mercury in the two limbs gives gauge pressure

Hence, gauge pressure is 20 cm of Hg.

Absolute pressure = Atmospheric pressure + Gauge pressure

                                =76+20=96cm of Hg

For figure (b)

Difference between the levels of mercury in the two limbs =–18cm

Hence, gauge pressure is –18 cm of Hg.

Absolute pressure = Atmospheric pressure + Gauge pressure

                                =76cm–18cm=58cm

(b)  13.6 cm of water is poured into the right limb of figure (b).

Relative density of mercury = 13.6

Hence, a column of 13.6 cm of water is equivalent to 1 cm of mercury.

Let h be the difference between the levels of mercury in the two limbs.

The pressure in the right limb is given as:

PR= Atmospheric pressure + 1 cm of Hg

        =76+1=77cm of Hg  ….. (i)

The mercury column will rise in the left limb.

Hence, pressure in the left limb, PL=58+h  ..... (ii)

Equating equations (i) and (ii), we get:

77=58+h

∴h=19cm

Hence, the difference between the levels of mercury in the two limbs will be 19 cm.