NCERT Solutions for Class 11 Geography (Fundamental of physical geography) Chapter 9 Atmospheric Circulation and Weather System
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Page 1
NCERT
SOLUTIONS
CLASS - 11th
aglase .co
SOLUTIONS
CLASS - 11th
aglase .co
Page 2
Book : Fundamental of Physical Geography Ncert Solutions | Chapter - 10 Social Science Geography
Class : 11th
Subject : Geography
Chapter : 10
Chapter Name : Atmospheric Circulation and Weather System
Q1 Multiple choice questions.
(i) If the surface air pressure is 1,000 mb, the air pressure at 1 km above the surface will be:
(a) 700 mb
(b) 1,100 mb
(c) 900 mb
(d) 1,300 mb
(ii) The Inter Tropical Convergence Zone normally occurs:
(a) near the Equator
(b) near the Tropic of Cancer
(c) near the Tropic of Capricorn
(d) near the Arctic Circle
(iii) The direction of wind around a low pressure in northern hemisphere is:
(a) clockwise
(b) perpendicular to isobars
(c) anti-clock wise
Page 1 of 7
Class : 11th
Subject : Geography
Chapter : 10
Chapter Name : Atmospheric Circulation and Weather System
Q1 Multiple choice questions.
(i) If the surface air pressure is 1,000 mb, the air pressure at 1 km above the surface will be:
(a) 700 mb
(b) 1,100 mb
(c) 900 mb
(d) 1,300 mb
(ii) The Inter Tropical Convergence Zone normally occurs:
(a) near the Equator
(b) near the Tropic of Cancer
(c) near the Tropic of Capricorn
(d) near the Arctic Circle
(iii) The direction of wind around a low pressure in northern hemisphere is:
(a) clockwise
(b) perpendicular to isobars
(c) anti-clock wise
Page 1 of 7
Page 3
Book : Fundamental of Physical Geography Ncert Solutions | Chapter - 10 Social Science Geography
(d) parallel to isobars
(iv) Which one of the following is the source region for the formation of air masses?
(a) the Equatorial forest
(b) the Himalayas
(c) the Siberian Plain
(d) the Deccan Plateau
Answer.(i) (c) 900 mb
(ii) (a) near the Equator
(iii) (c) anti-clock wise
(iv) (c) the Siberian Plain
Page : 93 , Block Name : Exercises
Q2 Answer the following questions in about 30 words.
(i) What is the unit used in measuring pressure? Why is the pressure measured at station level
reduced to the sea level in preparation of weather maps?
(ii) While the pressure gradient force is from north to south, i.e. from the subtropical high
pressure to the equator in the northern hemisphere, why are the winds north easterlies in the
tropics.
(iii) What are the geostrophic winds?
(iv) Explain the land and sea breezes.
Page 2 of 7
(d) parallel to isobars
(iv) Which one of the following is the source region for the formation of air masses?
(a) the Equatorial forest
(b) the Himalayas
(c) the Siberian Plain
(d) the Deccan Plateau
Answer.(i) (c) 900 mb
(ii) (a) near the Equator
(iii) (c) anti-clock wise
(iv) (c) the Siberian Plain
Page : 93 , Block Name : Exercises
Q2 Answer the following questions in about 30 words.
(i) What is the unit used in measuring pressure? Why is the pressure measured at station level
reduced to the sea level in preparation of weather maps?
(ii) While the pressure gradient force is from north to south, i.e. from the subtropical high
pressure to the equator in the northern hemisphere, why are the winds north easterlies in the
tropics.
(iii) What are the geostrophic winds?
(iv) Explain the land and sea breezes.
Page 2 of 7
Page 4
Book : Fundamental of Physical Geography Ncert Solutions | Chapter - 10 Social Science Geography
Answer.
(i) Millibar or Pascal is the unit for measuring pressure. Most widely used unit is kilo Pascal
expressed as hpa.
The pressure measured at station level is reduced to sea level in the preparation of weather
maps in order to eliminate the effect of altitude on pressure.
(ii) While the pressure gradient force is from north to south, i.e. from the subtropical high
pressure to the equator in the northern hemisphere, the winds north easterlies in the tropics
because the coriolis force acts perpendicular on the wind and deflects the wind to the right
direction in the northern hemisphere making the direction of the wind north easterly.
(iii) When isobars are straight and when there is no friction, the pressure gradient force is
balanced by the Coriolis force and the resultant wind blows parallel to the isobar. This wind is
known as the geostrophic wind.
(iv) The land and sea absorb and transfer heat differently. During the day the land heats up
faster and becomes warmer than the sea. Therefore, over the land the air rises giving rise to a
low pressure area, whereas the sea is relatively cool and the pressure over sea is relatively
high. Thus, pressure gradient from sea to land is created and the wind blows from the sea to the
land as the sea breeze.
In the night the reversal of conduction takes place. The land loses heat faster and is cooler than
the sea. The pressure gradient is from the land to the sea and hence land breeze results.
Page 3 of 7
Answer.
(i) Millibar or Pascal is the unit for measuring pressure. Most widely used unit is kilo Pascal
expressed as hpa.
The pressure measured at station level is reduced to sea level in the preparation of weather
maps in order to eliminate the effect of altitude on pressure.
(ii) While the pressure gradient force is from north to south, i.e. from the subtropical high
pressure to the equator in the northern hemisphere, the winds north easterlies in the tropics
because the coriolis force acts perpendicular on the wind and deflects the wind to the right
direction in the northern hemisphere making the direction of the wind north easterly.
(iii) When isobars are straight and when there is no friction, the pressure gradient force is
balanced by the Coriolis force and the resultant wind blows parallel to the isobar. This wind is
known as the geostrophic wind.
(iv) The land and sea absorb and transfer heat differently. During the day the land heats up
faster and becomes warmer than the sea. Therefore, over the land the air rises giving rise to a
low pressure area, whereas the sea is relatively cool and the pressure over sea is relatively
high. Thus, pressure gradient from sea to land is created and the wind blows from the sea to the
land as the sea breeze.
In the night the reversal of conduction takes place. The land loses heat faster and is cooler than
the sea. The pressure gradient is from the land to the sea and hence land breeze results.
Page 3 of 7
Page 5
Book : Fundamental of Physical Geography Ncert Solutions | Chapter - 10 Social Science Geography
Fig. Sea Breeze and Land Breeze
Page : 93 , Block Name : Exercises
Q3 Answer the following questions in about 150 words.
(i) Discuss the factors affecting the speed and direction of wind.
(ii) Draw a simplified diagram to show the general circulation of the atmosphere over the globe.
What are the possible reasons for the formation of subtropical high pressure over 300 N and S
latitudes?
Page 4 of 7
Fig. Sea Breeze and Land Breeze
Page : 93 , Block Name : Exercises
Q3 Answer the following questions in about 150 words.
(i) Discuss the factors affecting the speed and direction of wind.
(ii) Draw a simplified diagram to show the general circulation of the atmosphere over the globe.
What are the possible reasons for the formation of subtropical high pressure over 300 N and S
latitudes?
Page 4 of 7
Page 6
Book : Fundamental of Physical Geography Ncert Solutions | Chapter - 10 Social Science Geography
(iii) Why does tropical cyclone originate over the seas? In which part of the tropical cyclone do
torrential rains and high velocity winds blow and why?
Answer.
(i) The air in motion is called wind. The wind blows from high pressure to low pressure. The wind
at the surface experiences friction. The rotation of the earth also affects the wind movement.
Thus, the horizontal winds near the earth's surface respond to the combined effect of three
forces :–
➔ Pressure gradient force :- The differences in atmospheric pressure produces a force.
The rate of change of pressure with respect to distance is the pressure gradient. The
pressure gradient is strong where the isobars are close to each other and is weak where
the isobars are apart.
➔ Frictional force :- It affects the speed of the wind. It is greatest at the surface and its
influence generally extends upto an elevation of 1 - 3 km. Over the sea surface friction is
minimal.
➔ Coriolis force :- The rotation of the earth about its axis affects the direction of the
wind. This force is called the Coriolis force. It deflects the wind to the right direction in the
northern hemisphere and to the left in the southern hemisphere. The deflection is more
when the wind velocity is high. It is maximum at the poles and is absent at the equator.
(ii)
Fig. General circulation of the atmosphere over the globe
Page 5 of 7
(iii) Why does tropical cyclone originate over the seas? In which part of the tropical cyclone do
torrential rains and high velocity winds blow and why?
Answer.
(i) The air in motion is called wind. The wind blows from high pressure to low pressure. The wind
at the surface experiences friction. The rotation of the earth also affects the wind movement.
Thus, the horizontal winds near the earth's surface respond to the combined effect of three
forces :–
➔ Pressure gradient force :- The differences in atmospheric pressure produces a force.
The rate of change of pressure with respect to distance is the pressure gradient. The
pressure gradient is strong where the isobars are close to each other and is weak where
the isobars are apart.
➔ Frictional force :- It affects the speed of the wind. It is greatest at the surface and its
influence generally extends upto an elevation of 1 - 3 km. Over the sea surface friction is
minimal.
➔ Coriolis force :- The rotation of the earth about its axis affects the direction of the
wind. This force is called the Coriolis force. It deflects the wind to the right direction in the
northern hemisphere and to the left in the southern hemisphere. The deflection is more
when the wind velocity is high. It is maximum at the poles and is absent at the equator.
(ii)
Fig. General circulation of the atmosphere over the globe
Page 5 of 7
Page 7
Book : Fundamental of Physical Geography Ncert Solutions | Chapter - 10 Social Science Geography
The air at the Inter Tropical Convergence Zone (ITCZ) rises because of convection caused by
high insolation and a low pressure is created. The winds from the tropics converge at this low
pressure zone. The converged air rises along with the convective cell. It reaches the top of the
troposphere up to an altitude of 14 km. and moves towards the poles. This causes accumulation
of air at about 300 N and S. Part of the accumulated air sinks to the ground and forms a
subtropical high. Another reason for sinking is the cooling of air when it reaches 300N and S
latitudes.
Thus Subtropical High Pressure belt is formed over 300N and S latitudes.
(iii) Tropical cyclones are violent storms that originate over oceans in tropical areas and move
over to the coastal areas bringing about large scale destruction caused by violent winds, very
heavy rainfall and storm surges. Tropical cyclones originate and intensify over warm tropical
oceans. Tropical cyclone require large sea surface with temperature higher than 27°C. With
continuous supply of moisture from the sea, the storm is further strengthened.
A mature tropical cyclone is characterised by the strong spirally circulating wind around the
centre, called the eye. The diameter of the circulating system can vary between 150 and 250
km. The eye is a region of calm with subsiding air. Around the eye is the eye wall, where there
is a strong spiralling ascent of air to greater height reaching the tropopause. The wind reaches
maximum velocity in this region, reaching as high as 250 km per hour. Torrential rain occurs in
this zone. From the eye wall rain bands may radiate and trains of cumulus and cumulonimbus
clouds may drift into the outer region.
Page 6 of 7
The air at the Inter Tropical Convergence Zone (ITCZ) rises because of convection caused by
high insolation and a low pressure is created. The winds from the tropics converge at this low
pressure zone. The converged air rises along with the convective cell. It reaches the top of the
troposphere up to an altitude of 14 km. and moves towards the poles. This causes accumulation
of air at about 300 N and S. Part of the accumulated air sinks to the ground and forms a
subtropical high. Another reason for sinking is the cooling of air when it reaches 300N and S
latitudes.
Thus Subtropical High Pressure belt is formed over 300N and S latitudes.
(iii) Tropical cyclones are violent storms that originate over oceans in tropical areas and move
over to the coastal areas bringing about large scale destruction caused by violent winds, very
heavy rainfall and storm surges. Tropical cyclones originate and intensify over warm tropical
oceans. Tropical cyclone require large sea surface with temperature higher than 27°C. With
continuous supply of moisture from the sea, the storm is further strengthened.
A mature tropical cyclone is characterised by the strong spirally circulating wind around the
centre, called the eye. The diameter of the circulating system can vary between 150 and 250
km. The eye is a region of calm with subsiding air. Around the eye is the eye wall, where there
is a strong spiralling ascent of air to greater height reaching the tropopause. The wind reaches
maximum velocity in this region, reaching as high as 250 km per hour. Torrential rain occurs in
this zone. From the eye wall rain bands may radiate and trains of cumulus and cumulonimbus
clouds may drift into the outer region.
Page 6 of 7
Page 8
Book : Fundamental of Physical Geography Ncert Solutions | Chapter - 10 Social Science Geography
Fig. Vertical section of a Tropical Cyclone
Page : 93 , Block Name : Exercises
Page 7 of 7
Fig. Vertical section of a Tropical Cyclone
Page : 93 , Block Name : Exercises
Page 7 of 7
Document Details
| Board / Org | NCERT |
| Exam | Class 11 |
| Type | Solution |
| Pages | 8 |
| Updated | 30 Apr 2026 |