This worksheet provides a comprehensive set of questions for 9th-grade ICSE students to master the concepts of atmospheric pressure and barometers.

1. Atmospheric pressure is the force per unit area exerted by the weight of the atmosphere above a surface.
2. The numerical value of atmospheric pressure on the surface of the Earth is approximately 101,325 pascals (Pa).
3. Torr measures pressure. One torr is equal to 1/760 of a standard atmosphere, and 1 torr ≈ 133.322 Pa.
4. The S.I. unit of atmospheric pressure is the pascal (Pa). One bar equals 100,000 pascals (10⁵ Pa).
5. The physical quantity expressed in ‘atm’ is pressure. One atm = 101,325 pascals.
6. We do not feel uneasy because the pressure inside our bodies (e.g., blood pressure, air in lungs) balances the external atmospheric pressure.
7. Animals do not feel the pressure because their internal body pressures are in equilibrium with the surrounding atmospheric pressure.
8. The Magdeburg hemispheres experiment demonstrates air pressure: two hemispheres evacuated of air cannot be pulled apart easily due to external atmospheric pressure pushing them together.
9. When you suck on a straw, you reduce the pressure inside it; atmospheric pressure pushes the drink up the straw into your mouth.
10. Pressing the rubber bulb expels air, creating lower pressure inside the dropper; atmospheric pressure pushes liquid into the dropper. It cannot suck liquid in space because there is no atmospheric pressure.
11.
(i) Air pressure inside the balloon balances external atmospheric pressure; removing air removes this balance, so the higher external pressure collapses it.
(ii) Without pressing, the pressure inside the dropper equals atmospheric pressure, so liquid doesn’t flow out. Pressing reduces internal pressure, allowing atmospheric pressure to push liquid in.
(iii) One hole allows air to enter as oil flows out through the other, maintaining pressure balance; without air entry, pressure drop prevents flow.
12. Removing air from the tube reduces internal pressure; external atmospheric pressure compresses the tube, causing deflation.
13. Pulling the piston creates a low-pressure region in the syringe; atmospheric pressure pushes the liquid up into the barrel.
14. A water pump reduces pressure above the water in the well; atmospheric pressure pushes water up the pipe into the pump.
15. On the Moon, with no atmosphere, removing the lid would cause any volatile liquid to boil or evaporate rapidly due to lack of external pressure.
16. Instruments used include mercury barometer, aneroid barometer, and Fortin’s barometer.
17. A barometer is an instrument that measures atmospheric pressure. A simple barometer consists of a long glass tube filled with mercury, inverted into a mercury reservoir; the height of the mercury column indicates pressure.
18. Barometers forecast weather by detecting changes in atmospheric pressure: falling pressure often indicates storms; rising pressure suggests fair weather.
19. In a simple barometer, atmospheric pressure supports the mercury column. At equilibrium, atmospheric pressure equals the pressure exerted by the mercury column (P = ρgh), so height h directly measures atmospheric pressure.
20. “76 cm of Hg” means atmospheric pressure equals the pressure exerted by a 76 cm high column of mercury. Value in Pa: P = ρgh = (13,600 kg/m³)(9.8 m/s²)(0.76 m) ≈ 101,293 Pa.
21. [Diagram description: A vertical glass tube filled with mercury, inverted in a mercury dish. The mercury column stands at 76 cm above the dish level. The space above the mercury is vacuum. Label: “Atmospheric pressure supports 76 cm Hg column.”]
22. Barometric height is used because it directly relates to pressure via P = ρgh, and mercury’s high density makes the column manageable in size (76 cm vs. ~10 m for water).
23. The space above the mercury column in a barometer is vacuum because no air enters when the tube is inverted. This vacuum is called Torricelli’s vacuum.
24. [Diagram description: Fortin’s barometer has a glass tube with mercury, a leather bag base, and a vernier scale. A screw adjusts the mercury reservoir level to zero. It overcomes the defect of simple barometer by allowing precise measurement via vernier and eliminating errors from variable reservoir level.]