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explain the construction of a simple barometer 

Dear Student

A barometer is a devise used to measure the air pressure. It is generally used to measure atmospheric pressure.

A mercury barometer has a glass tube with a height of at least 84  cm , closed at one end, with an open mercury-filled reservoir at the base. The weight of the mercury creates a vacuum in the top of the tube. Mercury in the tube adjusts until the weight of the mercury column balances the atmospheric force exerted on the reservoir.

The pressure is quoted as the level of the mercury's height in the vertical column.One atmosphere (1 atm) is equivalent to 760 millimeters of mercury column. So the height of the mercury column varies according to external pressure on the mercury in reservoir.



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1 Dear student,
Gather the things you'll need. These consist of: Scissors, tape, a balloon, a jar, an elastic rubber band, a straw.
2 Blow up the balloon carefully and then let the air out of it again. (This is to stretch it.) 3 Cut the balloon in half. Discard the piece with the neck on it.

4Take the remaining piece of the balloon and stretch it across the glass or jar.Keep it stretched firmly across and seal it down with the rubber band, around the rim of the glass jar. To make an airtight seal, avoid gaps between the balloon and the glass. 5 Tape the straw onto the balloon lid; the straw should be sitting one quarter of a way on the lid, with the tape about 2 cm or 1 inch from the edge of the straw end that is sitting on the balloon lid. The straw is your indicator "needle". Trim the straw if it's too long, but leave more length off the jar as what is attached to it. 6 Put the finished glass jar next to a wall and tape a piece of paper or card to the wall behind it. 7 Mark the current position of the straw on the paper, and mark one above and below the mark, about the same length away, and label the high and low pressure. Arrange the paper so there is room above and below the straw for you to make more marks when the straw moves. 8 Check the straw regularly and keep marking its location on the paper for a few days. Add notes that tell you what the weather is like (for example, "rainy," "windy," or "sunny,") next to the mark.
  • Examine the paper after several days. Check the markings and the weather statements you've put next to them.


 
 
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