group 4 reporting
TRANSCRIPT
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GROUP 4
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PRINCIPLESOF
ANEROID
BAROMETER
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Aneroid barometeris an
instrument
measuring atmospheric pressure
invented by French scientist Lucien
Vidie. It is constructed on the
following principles:
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Parts of an Aneroid Barometer
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Principles of Mercurial Barometer
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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.
Invented by Evangelista
Toricilli
The weight of the mercury
creates a vacuum in the top
of the tube. Mercury in the
tube adjusts until the weightof the mercury column
balances the atmospheric
force exerted on the
reservoir.
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High atmospheric pressure places more forceon the reservoir, forcing mercury higher in thecolumn.
Low pressure allows the mercury to drop to a
lower level in the column by lowering theforce placed on the reservoir.
Since higher temperature at the instrument
will reduce the density of the mercury, thescale for reading the height of the mercury isadjusted to compensate for this effect.
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DISTINGUISHTHEATMOSPHERIC
PRESSUREREADINGOF ANEROIDBAROMETERANDTEMPERATURE
READING.
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To read your barometer, first tap the
glass lightly, but firmly, to ensure that
the linkage mechanism is not sticking.
The hectopascal is the international
meteorological unit of pressure. One
hectopascal is exactly equal to onemillibar, the unit of pressure mainly
used for barometer scales before
1986.
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The other hand that is found on
most instruments is the 'setpointer' (usually brass). This can
be turned by means of the knob
at the centre of the glass so that itcovers the reading pointer. In this
way you can tell, next time you
check your barometer, whether
the pressure is now lower or
higher and by how much.
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STATE THE FUNCTIONS OF
HYGROMETER AND EXPLAINTHEIR BASIC PRINCIPLES
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Hygrometer
Instrument used in finding the Dew - point
temperature .
It is always accompanied by a table which
shows the difference in dew point between
the dry-bulb temperature and the wet-bulb
temperature
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Example :
Dry bulb temperature (t) = 20.8C
Wet bulb temperature (t) = 19.4CCalculations:
you get t-t = 1.4 and t=19.4. In the table, you
can find:
Dew point temperature = 19.0 for t-t-1.0 and t-19.5(the
nearest value for 19.4)
Dew point temperature = 18.8 for t-t= 1.5 and t = 19.5.
then make the interpolation to get the dew-point
temperature for t-t = 1.4 and t = 19.5
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19.0+ (18.8-19.0)(1.4-1.0)/(1.5-1.0) = 18.8
Finally , make the interpolation to get the dew
point temperature for t-t = 1.4 and t = 19.4assuming the variance of t is approximately
the same with 18.8 0.1 = 19.7C