Page 117 - SST Class 07

fast and at night, it cools very fast. On the other Quiz Time
hand, the heating process of sea water is very
slow. This results the cool breeze from the sea Answer the questions :
during the day. In the night, the land is cooler, so 1. What is the importance of oxygen?
a cool breeze blows into the sea. These winds 2. Where do all the weather phenomena occur in
help to reduce the difference in the day and night the atmosphere?
temperatures of areas near the shoreline and there
is not much difference between summer and 3. In which layer of the atmosphere the aeroplanes
winter temperatures. fly?
4. Name two major elements of weather and
Altitude
climate.
As given earlier, the higher you go above the
ground level, the cooler it is. Temperature 5. At which point of the earth, the effect of
decreases by about 1°C for every 100 m increase insolation is very less?
in altitude. 6. What are the freezing and boiling points on the
Fahrenheit scale?
Info Bits
Info Bits Atmospheric Air Pressure

The weight of air pushing down on a unit area on
The temperature of air decreases with increasing
height at the rate of 1°C for every 165 m. This is the earth’s surface is called atmospheric pressure .
called the normal lapse rate. It is measured by the instrument called barometer
and the unit in which it is measured is milibar .
Surface Type The normal atmospheric pressure at sea level is

The surface of a town or a city with lots of about 76 cm of the mercury column in the
concrete structures, will absorb more of insolation barometer. Polar HP
than a forest or the moist soil surface of a village. Polar Easterlies
So temperatures in cities or towns are greater than Sub-polar LP 60°N-65°N
in rural areas. Similarly, the barren surface of the South-Westerly Winds
Sub-tropical HP 30°N-35ºN
desert heats up quickly.
North-East Trade Winds
Measurement of Temperature : Temperature is 0°
measured by an instrument called the South-East Trade Winds
thermometer. It measures the atmospheric Sub-tropical HP 30°S-35°S
temperature on a Fahrenheit or a Celsius scale. North-Westerly Winds
Sub-polar LP 60°S-65°S
On the Fahrenheit scale, the freezing point is
Polar Easterlies
32°F and the boiling point is 212°F. On the Polar HP
Celsius scale, the freezing point is 0°C and the Pressure Belts
boiling point is 100°C. We can convert the Factors Affecting Atmospheric Pressure
Fahrenheit reading into celsius reading or vice Temperature and altitude are two factors which
versa using the following formulae :
influence atmospheric pressure. Air expands on
°F = °C × + 329 9 °C = (°F – 32) × 5 being heated and becomes light. This hot air then
5 9 rises upwards, creating areas of low pressure. Low
pressure is associated with cloudy sky and wet
Info Bits
Info Bits weather. In contrast, the cold air contracts, and
becomes heavy and settles down creating an area
The Fahrenheit scale was invented by Daniel of high pressure. High pressure is associated with
Fahrenheit and the Celsius scale was invented by clear and sunny sky. Atmospheric pressure is also
Andres Celsius. In India, Celsius scale is generally affected by the rotation of the earth.
used.
The Atmosphere
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