ZIMSEC O Level Geography Notes: Pressure.
-is the pressure exerted by the weight of air in the atmosphere of Earth. It is measured in millibars. It is measured using an instrument known as a barometer. There are two different types of barometers: the mercury and aneroid barometers.
- It is very large, the glass tube is typically almost 1m in height.
- It gives very accurate readings.
- It has a bulb that is dipped in a container of mercury.
- When the atmospheric pressure rises, it exerts force its force on the mercury which becomes compressed.
- The mercury is pushed up the bulb to a height of 760 mm.
- When pressure decreases the mercury contracts and moves down the thermometer.
- It gives accurate readings.
- It is simple to construct and maintain.
- It is very large and cumbersome.
- Mercury must be at least a meter long.
- They break easily.
- They cannot produce a continuous reading, so readings have to be taken regularly.
- Mercury is a dangerous poison.
- These are portable and can be safely used at homes and schools as they do not contain mercury.
- They are made up of an air-tight metal box.
- If pressure increases the box is squashed inwards.
- Conversely if pressure decreases the box expands outwards.
- A complex series of springs is attached to the box.
- The other end of the spring is connected to a point which has a calibrated dial on the other end to record the various pressure readings.
- The spring amplifies the expansions and contractions of the box in accordance to atmospheric pressure.
- It is portable.
- It can be safely used in the home or at school since it does not rely on mercury which is poisonous.
- It is easier to read since it comes with a calibrated dial.
- Can make continuous readings.
- Can be attached to a computer to make automated continuous readings.
- It is less accurate.
- Requires great skill and expertise to make.
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