Many waterfalls occur where rivers flow over hard rocks which overlie softer ones. The hard rocks resist erosion, while the softer rocks are worn away. The hard lip of the waterfall often overhangs the softer rocks and slabs of hard rock sometimes break off and crash downwards. In this way, waterfalls, like southern Africa’s Victoria Falls (whose African name means …

The ozone layer contains ozone molecules – O3 molecules – which are formed by the action of ultra-violet rays on atmospheric oxygen. This oxygen, which is O2, converts into O3 when UV rays fall on it. When these rays fall on the surface of the atmosphere, they are absorbed in the conversion of oxygen into ozone. As a result, ultra-violet …

Maximum and minimum temperatures are measured using thermometers mounted inside a wooden box with slits, called Stevenson’s screen, which is generally kept facing north. The maximum thermometer is mercury-in-glass – as the temperature rises, the mercury expands and moves freely up a constriction in the thermometer. When air temperature drops, the constriction prevents the mercury from flowing back due to …

In the 19th century, geologists could tell whether one rock layer was older or younger than another by the fossils they contained. But they could not measure the absolute ages of rocks until after the discovery of radioactivity in the 1890s. Radioactive substances, which are occasionally found in rocks, give off high-energy rays and decay (break down) at a fixed …

Sunset occurs when the upper edge of the sun — called the upper limb — sinks just under the horizon; sunrise occurs when the upper limb rises just above the horizon.

Stem cells, which hold the promise of new cell-based therapies to treat critical medical conditions, have to be effectively stored until it’s time to use them. The method is called cryopreservation: it freezes stem cells at temperatures below -150 o C, by immersing them in nitrogen vapour. But if the cells are to survive this process, they need to be …

Points or index refers to a figure indicative of the health of the stock market. The most widely used index is sensex or sensitive index which is based on weighted value of 30 numbers of most traded shares in the Mumbai stock exchange. Each stock has a percentage share in a total of 100 and affects the value of the …

International Telecommunication Union (ITU) recommendation defines the international public telecommunication numbering plan used in the PSTN. It also defines the format of phone numbers. As per these recommendations, numbers can have a maximum of 15 digits and are usually written with a + prefix. CCITT, the predecessor of the ITU Telecommunication Standardization Sector, developed the first formal list of telephone …

Electric pylons are tall supports – made of galvanised steel lattice, steel tube or wood – used for power line construction. In normal terrain, they are assembled on the site. In mountainous regions, helicopters are used for power line construction, which are efficient but expensive. In the aerial construction method, the entire structure is pre-assembled and shifted in helicopters.

It was not before sixteenth century, an Italian doctor named Jerome Cardan got the idea of teaching deaf-mutes through written characters. As a result of his work finger alphabets were developed, similar to the finger alphabets used today. With the help of finger alphabets, a deaf-mute makes the letters with his fingers and spells out words. He also depends on …