Atmospheric Pressure and Gauge Pressure - UNSOLVED PRACTICE SET

Q7. Distinguish between absolute pressure, gauge pressure, and atmospheric pressure. Write the relationship between them.

Q8. Explain the working of a simple mercury barometer. Why is mercury used instead of water?

Q9. Calculate the height of a water column that would exert the same pressure as 76 cm of mercury column. (Density of mercury = 13.6 g/cm³)

Q10. In your school, a student takes a sealed plastic bottle on a trip to Shimla. At higher altitude, the bottle appears swollen. Explain this using atmospheric pressure concepts.

Q11. A pressure gauge reads 2.5 × 10⁵ Pa. What is the absolute pressure if atmospheric pressure is 1.01 × 10⁵ Pa?

Q12. Why does a straw not work on the Moon? Explain using the concept of atmospheric pressure.

Q13. Explain the concepts of atmospheric pressure, absolute pressure, and gauge pressure. Describe the construction and working of:

(i) A mercury barometer

(ii) An open-tube manometer

(iii) A Bourdon gauge

Discuss why atmospheric pressure decreases with altitude and derive the approximate relation P = P₀e^(-Mgh/RT).

Q14. A mercury barometer reads 76 cm at sea level. It is taken to a hill station where it reads 70 cm.

(a) Calculate the atmospheric pressure at the hill station in Pa.

(b) If the density of air is 1.2 kg/m³, estimate the altitude of the hill station.

(c) A sealed bottle at sea level has air at 1 atm pressure. What is the gauge pressure of this air at the hill station?

(d) Explain why aircraft cabins are pressurised.

(e) Calculate the boiling point of water at this altitude if it decreases by 1°C for every 300 m rise.

Q15. Analyse the following measuring instruments:

(i) Mercury barometer

(ii) Aneroid barometer

(iii) Fortin's barometer

For each instrument, discuss:

(a) Principle of working

(b) Advantages and disadvantages

(c) Typical applications

(d) Sources of error

Q16. A U-tube manometer containing mercury is connected to a gas cylinder. The mercury level in the limb connected to the gas is 20 cm lower than in the open limb.

(a) Calculate the gauge pressure of the gas in Pa.

(b) Calculate the absolute pressure of the gas.

(c) If the gas is now compressed and the mercury difference becomes 30 cm (gas side lower), calculate the new gauge pressure.

(d) The gas is now connected to the other side and the mercury difference is 15 cm (gas side higher). What does this indicate?

(e) Design a simple school-level experiment to demonstrate gauge pressure using a manometer.

Q17. An aircraft flies at an altitude where the atmospheric pressure is 0.5 × 10⁵ Pa. The cabin is pressurised to 0.8 × 10⁵ Pa.

(a) Calculate the gauge pressure inside the cabin.

(b) If the cabin door has an area of 2 m², calculate the net force on the door.

(c) Why must the door open outward (toward lower pressure)?

(d) If there is a small hole of area 1 cm² in the fuselage, calculate the initial force trying to push air out.

(e) Discuss why rapid decompression is dangerous for passengers.

Q18. In a school science fair, students build a simple barometer using a glass tube, mercury, and a dish.

(a) Describe the step-by-step procedure to set up the barometer.

(b) If the mercury column stands at 75.5 cm on a particular day, calculate the atmospheric pressure.

(c) The next day, the column falls to 74 cm. What weather change does this indicate?

(d) Calculate the pressure difference between the two days.

(e) Discuss two safety precautions when handling mercury in school laboratories.