NCERT Class 11 Geography Glossary

Abiotic : Non-living thing. Usually refers to the physical and chemical components of an organism’s environment.

Adiabatic Lapse Rate : The rate of change of temperature by an ascending ordescending airmass. If no other non-adiabatic processes (i.e. no heat enters or leaves the system) occur (like condensation, evaporation and radiation), expansion causes the parcel of air to cool at a set rate of 0.98° per 100 m. The opposite occurs when a parcel of air descends in the atmosphere. The air in a descending parcel becomes compressed. Compression causes the temperature within the parcel to increase at a rate of 0.98° per 100 m.

Air Mass : A body of air whose temperature and humidity characteristics, acquired in source region, remain relatively constant over a horizontal distance of hundreds to thousands of km. Air masses develop their climatic characteristics by remaining stationary over a source region for a number of days. Air masses are classified according to their temperature and humidity characteristics.

Aphelion : It is the point in the Earth’s orbit when it is farthest from the sun (152.5 million km). Aphelion occurs on the 3rd or 4th of July.

 Asthenosphere : Zone in the Earth’s mantle that exhibits plastic properties. Located below the lithosphere at between 100 and 200 km. Atmospheric Pressure : Weight of the atmosphere on a surface. At sea-level, theaverage atmospheric pressure is 1013.25 mb. Pressure is measured by a device called a barometer.

Aurora : Multicoloured lights that appear in the upper atmosphere (ionosphere) over the polar regions and visible from locations in the middle and high latitudes. Caused by the interaction of solar wind with oxygen and nitrogen gas in the atmosphere. Aurora in the Northern Hemisphere are called aurora borealis and aurora australis in the Southern Hemisphere.

Bajada : Consecutive series of alluvial fans forming along the edge of a linear mountain range. Surface of this feature undulates in a rolling fashion as one moves from the centre of one alluvial fan to another. Normally occur in arid climates.

Batholith : A large mass of subsurface intrusive igneous rock that has its origins from mantle magma.

Big Bang : Theory about the origin of universe. It suggests that about 15 billion years ago all of the matter and energy in the Universe was concentrated into an area smaller than an atom. At this instant, matter, energy, space and time were not existant. Then suddenly with a bang, the Universe began to expand at an incredible rate and matter, energy, space and time came into being. As the Universe expanded, matter began to coalesce into gas clouds, and then stars and planets. Some scientists believe that this expansion is finite and will one day cease. After this point in time, the Universe will begin to collapse until a Big Crunch occurs.

Biodiversity : The diversity of different species (species diversity), genetic variability among individuals within each species (genetic diversity), and variety of ecosystems (ecosystem diversity).

Biomass : The weight of living tissues usually measured per unit area over a

Please refer to attached file for NCERT Class 11 Geography Glossary