Question

One arm of a glass U-tube is open to the atmosphere, whereas the other vertical arm is connected to a gas supply. The difference in levels of mercury (density = 13.6 g cm^-3) between the vertical arms of the U-tube manometer is h = 3 cm. If the atmospheric pressure is 760 mm Hg and the gravitational acceleration is 9.8 m s^-2, then the pressure of the gas is about:

• A. 1.074 $\times {10}^4$ dynes cm^-2
• B. 3.998 $\times {10}^6$ cm^-2
• C. 1.053 $\times {10}^5$ dynes cm^-2
• D. 1.017 $\times {10}^6$ dynes cm^-2

Answer 1

The correct option is C

1.053 $\times {10}^5$ dynes cm^-2

Pressure of gas = Atmospheric pressure + Pressure due to difference in mercury levels
= (76 + 3) cm Hg.
Pressure of gas = ρ g h
= (13.6 g/cm³) (980 cm/s²) (76 + 3) cm
= 1.053 $\times {10}^6$ dynes cm^-2