Physical and World Geography: key facts and practice questions

Revise Physical and World Geography for SSC, Railway, police and state PSC exams: the facts and distinctions that keep coming up, a one-glance revision list, and 10 practice questions with answers and explanations.

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Key concepts and facts

• Solar system and earth's motions: The planets from the Sun are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Jupiter is the largest, Mercury the smallest, Venus the hottest. The Earth's axis is tilted 23.5 degrees from the perpendicular (66.5 degrees from the orbital plane), and this tilt, not distance from the Sun, causes seasons. Perihelion is about 3 January, aphelion 4 July. On 21 June the Sun is overhead at the Tropic of Cancer (summer solstice, longest day in the Northern Hemisphere), on 22 December at the Tropic of Capricorn, and on 21 March and 23 September at the Equator (equinoxes). A solar eclipse occurs on a new-moon day when the Moon comes between the Sun and Earth; a lunar eclipse on a full-moon day when the Earth comes between them.
• Latitudes, longitudes and time: The Tropics lie at 23.5 N and S and the Arctic and Antarctic Circles at 66.5 N and S. The Prime Meridian passes through Greenwich; the Date Line roughly follows 180 degrees. 15 degrees of longitude = 1 hour and 1 degree = 4 minutes; places east of Greenwich are ahead. IST is based on 82.5 degrees E, 5 hours 30 minutes ahead of GMT. Crossing the Date Line from west to east you set the date back a day; from east to west you advance it.
• Interior, rocks and plate tectonics: The crust (SIAL over SIMA), mantle and core (NIFE) are separated by the Moho (crust-mantle), Gutenberg (mantle-core) and Lehmann (outer-inner core) discontinuities. Granite is intrusive igneous and basalt extrusive; sedimentary rocks are layered and hold fossils; metamorphism turns limestone into marble, sandstone into quartzite, shale into slate and granite into gneiss. Alfred Wegener proposed continental drift (Pangaea); the Indian and Eurasian plates collided to raise the Himalayas; the Pacific Ring of Fire has most active volcanoes. An earthquake starts at the focus and the surface point above it is the epicentre; Richter measures magnitude, Mercalli intensity; S waves cannot cross the liquid outer core. Barren Island (Andaman) is India's only active volcano.
• Landforms and mountains: Rivers cut V-shaped valleys and waterfalls in youth, form meanders in maturity and ox-bow lakes and deltas in old age. Glaciers carve U-shaped valleys, cirques and fjords and deposit moraines. Wind makes mushroom rocks, yardangs, barchans and loess. Groundwater in limestone makes karst caves with stalactites (ceiling) and stalagmites (floor). Young fold mountains are the Himalayas, Alps, Andes (longest range) and Rockies; block mountains (Black Forest, Vosges, Satpura) form by faulting. Elbrus (Caucasus) is the highest peak of Europe.
• Atmosphere, winds and climate: Air is 78 per cent nitrogen, 21 per cent oxygen, 0.93 per cent argon and 0.04 per cent carbon dioxide. The troposphere holds the weather (temperature falls 6.5 degrees C per km); the stratosphere holds the ozone layer; the ionosphere reflects radio waves. Albedo is the share of insolation reflected to space. The equatorial low is the doldrums and the subtropical highs the horse latitudes. Trade winds are north-easterly in the Northern Hemisphere; southern westerlies are the Roaring Forties; the Coriolis force deflects winds right in the north and left in the south (Ferrel's law). Local winds: Chinook (Rockies), Foehn (Alps), Loo (north India), Mistral (France, cold), Sirocco (Sahara to Italy), Harmattan (West Africa). Rainfall is convectional (equatorial 4 o'clock rain), orographic (with a rain shadow) or cyclonic; cumulonimbus clouds give thunderstorms and hail. Tropical cyclones are hurricanes (Atlantic), typhoons (western Pacific), willy-willies (Australia) and baguios (Philippines); they rotate anticlockwise in the north and cannot form near the Equator where the Coriolis force is absent; anticyclones bring fair weather.
• Oceans: The Pacific is the largest and deepest (Mariana Trench). Average salinity is 35 parts per thousand; the Red Sea is among the saltiest seas, the Baltic the least salty. Warm currents: Gulf Stream, Kuroshio, Brazil, Agulhas. Cold currents: Labrador, Canary, Benguela, Peru (Humboldt), Oyashio, California. Where they meet (Grand Banks) fog forms and fishing is rich. Spring tides come on new and full moon, neap tides at the quarters. El Nino is unusual warming off Peru that weakens the Indian monsoon; La Nina is the opposite.
• World features, countries and superlatives: Sahara is the largest hot desert, Antarctica the largest overall, Atacama the driest. Nile is the longest river, Amazon the largest by volume, Volga the longest in Europe. Caspian is the largest lake, Superior the largest freshwater lake, Baikal the deepest. Angel Falls (Venezuela) is the highest waterfall. Grasslands: prairies (North America), pampas (Argentina), steppes (Eurasia), savanna (Africa), downs (Australia), veld (South Africa). Straits: Malacca (Indian Ocean-South China Sea), Hormuz (Persian Gulf-Gulf of Oman), Bab-el-Mandeb (Red Sea-Gulf of Aden), Bering (Russia-Alaska). Canals: Suez (Mediterranean-Red Sea, 1869), Panama (Atlantic-Pacific, 1914). Kazakhstan is the largest landlocked country; Uzbekistan and Liechtenstein are doubly landlocked. Greenland is the largest island, Russia the largest country, Vatican City the smallest.
• Common traps: 23.5 degrees is the tilt from the perpendicular, 66.5 from the orbital plane; S waves, not P waves, stop at the outer core; the Brazil current is warm while the Benguela is cold; Bangladesh is neither landlocked nor a neighbour of China.

One-glance revision list

• Planet order mnemonic: My Very Educated Mother Just Served Us Noodles = Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Jupiter is largest, Mercury smallest, Venus hottest.
• Time rule: 15 degrees of longitude = 1 hour, 1 degree = 4 minutes. IST is on 82.5 degrees E, so noon at Greenwich is 5:30 pm in India.
• Overhead Sun: 21 June on the Tropic of Cancer, 22 December on the Tropic of Capricorn, 21 March and 23 September on the Equator (equinoxes).
• Discontinuities from top to bottom: Conrad (within crust), Moho (crust-mantle), Gutenberg (mantle-core), Lehmann (outer core-inner core).
• Metamorphic pairs: limestone to marble, sandstone to quartzite, shale to slate, granite to gneiss, coal to graphite.
• Richter = magnitude (energy released), Mercalli = intensity (observed damage, I to XII). Focus is underground, epicentre is the surface point above it.
• Local winds: Chinook (Rockies, snow eater), Foehn (Alps), Mistral (France, cold), Sirocco (Sahara to Italy, hot), Harmattan (West Africa, the Doctor), Loo (north India).
• Cyclone names by region: hurricane (Atlantic and Caribbean), typhoon (China Sea and Japan), willy-willy (Australia), baguio (Philippines), cyclone (Indian Ocean).
• Cold currents: Labrador, Canary, Benguela, Peru (Humboldt), Oyashio, California. Warm currents: Gulf Stream, Kuroshio, Brazil, Agulhas.
• Grasslands by continent: Prairies (North America), Pampas (Argentina), Steppes (Eurasia), Savanna (Africa), Downs (Australia), Veld (South Africa), Llanos (Venezuela).
• Superlatives: Nile longest river, Amazon largest by volume, Caspian largest lake, Baikal deepest lake, Sahara largest hot desert, Greenland largest island, Angel Falls highest waterfall.
• Capital traps: Australia is Canberra (not Sydney), Canada is Ottawa, Turkey is Ankara, Switzerland is Bern, Brazil is Brasilia, New Zealand is Wellington.

Practice questions

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Where this is tested

Physical and World Geography is tested in SSC, Railway, police and state PSC exams. Check the current official notification and syllabus of the exam you are preparing for to see how it is covered.

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