Natural Phenomena, Energy Sources and Space

Natural phenomena

• Lightning: caused by discharge of electric charge between clouds or between a cloud and the ground. Benjamin Franklin showed lightning is electrical. Thunder is the sound; lightning is seen first because light is faster.
• Safety in thunderstorms: stay indoors, avoid open fields, tall trees, metal and water; use lightning conductors.
• Earthquake: sudden release of energy in the Earth's crust, producing seismic waves. Recorded by a seismograph on the Richter scale (magnitude) or the Mercalli scale (intensity). The epicentre is the point on the surface above the focus. Waves: P (primary), S (secondary), L (surface).
• Cyclone, tsunami and volcano are other natural hazards. Tsunami is caused mainly by undersea earthquakes.
• Static electricity: charged objects attract light things.

Sources of energy

• Fossil fuels (coal, oil, gas) formed over millions of years from dead organisms; burning them causes air pollution, greenhouse gases and acid rain.
• Hydroelectric power: the PE of stored water turns turbines. Tehri, Bhakra Nangal, Baglihar and Salal are examples; J&K has high hydro potential on the Chenab and Jhelum.
• Thermal power: burning coal; India's main source of electricity.
• Solar energy: solar cells (photovoltaic) convert sunlight to electricity; solar cookers, heaters, panels. A solar constant is about 1.4 kW/m^2.
• Wind energy: windmills and wind turbines; Muppandal in Tamil Nadu is among the largest wind farms.
• Biogas: from cow dung and organic waste; mainly methane (about 65 to 70%); the leftover slurry is a good manure. Made in gobar gas plants.
• Biomass: wood, dung cakes, crop residue.
• Geothermal: heat from within the Earth. Tidal: from ocean tides. Ocean thermal (OTEC): from temperature difference of sea water.
• Nuclear energy: from nuclear fission (splitting of heavy nuclei like uranium-235) or fusion (joining of light nuclei like hydrogen, as in the Sun and stars). Nuclear reactors use fission. Hydrogen bomb uses fusion. Chain reaction and control rods (cadmium, boron) are key terms.
• Nuclear power plants in India: Tarapur, Kalpakkam, Kudankulam, Rawatbhata, Narora, Kakrapar, Kaiga.
• Radioactivity was discovered by Henri Becquerel; Marie Curie and Pierre Curie found polonium and radium. Alpha (helium nucleus), beta (electron), gamma (photon) rays; gamma has the highest penetration.

Good fuel and calorific value

• Calorific value is the heat produced by burning 1 kg of fuel (kJ/kg). Hydrogen has the highest calorific value; LPG and CNG are cleaner than coal and petrol.

Space and the solar system

• Pluto was reclassified as a dwarf planet in 2006 (IAU), along with Ceres, Eris, Haumea, Makemake.
• Asteroids (mostly between Mars and Jupiter), comets (ice and dust with a tail pointing away from the Sun; Halley's comet returns about every 76 years), meteors ("shooting stars") and meteorites (reach the ground).
• Moon: Earth's only natural satellite; no atmosphere; takes about 27.3 days to orbit; the same face always shows to Earth; Neil Armstrong first walked on it (Apollo 11, 1969). Chandrayaan-3 landed near the Moon's south pole in August 2023, making India the fourth country to soft-land and the first at the south polar region.
• Phases of the Moon: new moon (Amavasya), full moon (Purnima), waxing and waning. Solar eclipse: Moon between Sun and Earth (at new moon). Lunar eclipse: Earth between Sun and Moon (at full moon).
• Day and night are due to rotation (24 hours); seasons are due to revolution and the tilt of the axis (23.5 degrees).
• Stars form in nebulae; constellations include Ursa Major (Saptarishi), Orion. The Pole Star (Polaris) appears fixed in the north. The nearest star after the Sun is Proxima Centauri. Galaxy: our galaxy is the Milky Way; the nearest large galaxy is Andromeda.
• Black hole: a region of extreme gravity from which not even light can escape.

Artificial satellites and ISRO

• Geostationary satellites orbit at about 36,000 km above the equator, with a period of 24 hours, so they appear fixed; used for communication and TV. Polar (sun-synchronous) satellites orbit at about 700 to 800 km and are used for remote sensing and weather.
• Sputnik 1 (USSR, 1957) was the first artificial satellite. Yuri Gagarin was the first human in space (1961). Valentina Tereshkova was the first woman.
• ISRO was founded in 1969 (headquarters Bengaluru), after INCOSPAR (1962); Vikram Sarabhai is the father of the Indian space programme.
• Aryabhata (1975) was India's first satellite. Rakesh Sharma was the first Indian in space (1984). Kalpana Chawla was the first Indian-origin woman in space.
• Chandrayaan-1 (2008) found water on the Moon; Mangalyaan (Mars Orbiter Mission, 2013) made India the first country to reach Mars orbit on its first try; Aditya-L1 (2023) studies the Sun; Gaganyaan is the human-spaceflight programme. Launch site: Sriharikota; rockets: PSLV, GSLV, LVM3.