Worksheet 3.3 Understanding Gas Pressure and Atmospheric Pressure

1.

Figure shows a manometer connected to a gas tank whose valve is then turned on. What is the pressure of the gas , in unit N m-2 , in the tank?[Density of water = 1 000 kg m-3]

Answer : 1 000 N m-2

2.

The siphon is filled with mercury until B and released. While the mercury is flowing out from B, what is the pressure at A, in unit of cm Hg ?[Atmospheric pressure = 76 cm Hg]

Answer : 70 cm Hg

3.

4.

5.

6.

What is the pressure of the gas strapped inside the J-tube , in unit Pa?

Answer : 1.19 x 105 Pa

If the atmospheric pressure is 76 cm Hg, what is the pressure of the trapped air P ?

Answer : 66 cm Hg

Some air is trapped in part X of a barometer. If the atmospheric pressure is 75 cm Hg, what is the pressure of the air in X, in unit cm Hg ?

Answer : 25 cm Hg

Figure shows a manometer is used to determine the density of liquid X. If the density of water is 1 000 kg m-3, what is the density of liquid X ?

Answer : 800 kg m-3

7. Figure shows an U-tube filled with mercury and water. [Density of water = 1 x 103 kg m-3 , density of mercury = 13.6 x 103 kg m-3 ; Atmospheric pressure = 1 x 105 Pa]

(a) Calculate the pressure at Y due to water in N m-2.

(b) What is the height of the mercury column , h ?

(c) State the change to the mercury column , h, if water is replaced by alcohol .

……………………………………………………………………………………………...

(d) Explain why the mercury column , h changes as stated in (d) .

……………………………………………………………………………………………...

8.

(c) State the change to the length of mercury column above the mercury surface if

(i) the tube is raised by 10 cm. ……………………………………………….

(ii) the surrounding temperature increases ……………………………………………..

(iii) the instrument is brought to the peak of a mountain. …………………………….....

(iv) Water vapour is added to the vacuum region ………………………………………

water

Diagram shows a set up of apparatus for measuring atmospheric pressure.

(a) What is the name for the instrument ?

…………………………………………………….(b) Determine the atmospheric pressure as measured by

the instrument ,(i) in the unit cm Hg

(ii) in the unit Pa.