Physics

Physics -instruments of gas pressure and atmospheric pressure

1. INSTRUMENTS FOR MEASURING GAS PRESSURE U-tube manometer Bourdon gauge

2. U-TUBE MANOMETER The gas whose pressure is to be measured is connected directly to one side of the U-tube. The pressure of the gas is equal to the sum of atmospheric pressure and the pressure due to the difference in the height of the liquid in the manometer.

3. BOURDON GAUGE Commonly used in school laboratories, air conditioner service shops, hospitals and factories. When a Bourdon gauge is attached to a gas cylinder, gas flows from the cylinder into the flattened curved tube in the gauge. The pressure of the gas causes the curved tube to straighten out. Through a lever and a gear system, the pointer rotates to measure the pressure of the gas.

4. INSTRUMENTS FOR MEASURING ATMOSPHERIC PRESSURE Mercury barometer Fortin barometer Aneroid barometer

5. MERCURY BAROMETER Made by inverting a long glass tube filled with mercury. Due to the inversion, a vacuum is created at the base of the tube and a column of mercury is supported by the atmospheric pressure. The units for the measurement of atmospheric pressure can be in terms of centimeters of mercury (cm Hg) or Pascal (Pa). Another unit of pressure is torr , where 1 torr is equal to 1 mm Hg.

6. FORTIN BAROMETER Essentially modified from a simple mercury barometer. The Fortin barometer has a metal scale with a vernier attached and a mirror behind the top of the mercury column to avoid parallax error when taking readings. With these features, the Fortin barometer measures the atmospheric pressure more accurately than the simple mercury barometer.

7. ANEROID BAROMETER More convenient form of barometer because it does not use liquid and can be as small as a wristwatch. Inside an aneroid barometer there is a partially evacuate metal case made of thin and flexible alloy. A change of atmospheric pressure will cause the centre of the metal case to move in or out. This movement is magnified by a system of levers. A chain attached to the last lever rotates the pointer to show the atmospheric pressure measured.