Question 1

Q1: (iii) The direction of wind around a low pressure in northern hemisphere is: (a) clockwise (b) perpendicular to isobars (c) anti-clock wise (d) parall...

Accepted Answer

(c) anti-clock wise According to the chapter, the circulation of wind around a low-pressure system is called cyclonic circulation. Due to the effect of the Coriolis force, which deflects winds to the right in the Northern Hemisphere, the wind circulates in an anti-clockwise direction around a low-pr...

Question 2

Q1: (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 Pla...

Accepted Answer

(c) the Siberian Plain An air mass forms when air remains over a homogenous area for a long time, acquiring the characteristics of that surface. The chapter lists "The very cold snow covered continents in high latitudes" as a major source region. The Siberian Plain is a vast, homogenous, snow-covere...

Question 3

Q1: Multiple choice questions. (i) If the surface air pressure is $1,000 \mathrm{mb}$, the air pressure at 1 km above the surface will be: (a) 700 mb (b)...

Accepted Answer

(c) 900 mb As stated in the chapter, in the lower atmosphere, the atmospheric pressure decreases with height at a rate of about 1 mb for each 10 m increase in elevation.  Therefore, for an increase of 1 km (which is equal to 1,000 m), the pressure decrease would be: (1,000 m / 10 m) * 1 mb = 100 mb....

Question 4

Q1: (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...

Accepted Answer

(a) near the Equator The chapter mentions that near the equator, the sea level pressure is low, and this area is known as the equatorial low. The air at the Inter Tropical Convergence Zone (ITCZ) rises due to high solar insolation, creating this low-pressure zone. The winds from the tropics converge...

Question 5

Q2: (iv) Explain the land and sea breezes.

Accepted Answer

Land and sea breezes are local winds caused by the differential heating of land and sea.    Sea Breeze: During the day, land heats up faster than the sea, creating a low-pressure area over the land. The cooler, denser air from the high-pressure area over the sea blows towards the land. This is calle...

Question 6

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 reduc...

Accepted Answer

The unit used for measuring atmospheric pressure is the milibar (mb). Pressure measured at a station is reduced to sea level for weather maps to eliminate the effect of altitude on pressure readings. This allows for an accurate comparison of pressure between different locations at a standard level,...

Question 7

Q2: (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...

Accepted Answer

Winds do not blow directly from high to low pressure due to the Earth's rotation. The Coriolis force deflects moving air to the right in the Northern Hemisphere. Therefore, the wind moving south from the subtropical high towards the equatorial low is deflected to its right, turning it into a northea...

Question 8

Q2: (iii) What are the geotrophic winds?

Accepted Answer

Geostrophic winds are winds in the upper atmosphere, typically 2-3 km above the surface, where the effect of friction is negligible. They occur when the pressure gradient force is balanced by the Coriolis force. As a result, the geostrophic wind blows parallel to the isobars.

Question 9

Q3: Answer the following questions in about 150 words. (i) Discuss the factors affecting the speed and direction of wind.

Accepted Answer

The speed and direction of wind near the Earth's surface are controlled by the combined effect of three primary forces: the Pressure Gradient Force, the Frictional Force, and the Coriolis Force.    Pressure Gradient Force: This is the initial force that sets air in motion. It is produced by differen...

Question 10

Q3: (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 wh...

Accepted Answer

Tropical cyclones originate over warm tropical oceans because they require a continuous supply of heat and moisture, which only large bodies of warm water can provide. The key conditions for their formation are:    A large sea surface with a temperature higher than 27°C.    The presence of the Corio...

Question 11

Q3: (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 su...

Accepted Answer

The general circulation of the atmosphere involves three main cells in each hemisphere: the Hadley Cell, the Ferrel Cell, and the Polar Cell. (A diagram would show these three cells, with rising air at the equator and 60° latitudes, and sinking air at 30° latitudes and the poles, along with surface...

NCERT Solutions