Category Physics

What is Black hole?

A black hole is a fascinating and mysterious astronomical body. It is so-called because it gives off no light and sucks in whatever matter and energy that comes near it. It is the end product left behind after the death of a very massive star.

All stars have a life-cycle — they are born, grow old and finally die. The way they end up depends on the mass they start with. If the star is very massive — more than 30 times as massive as the sun, the end comes in a blinding explosion known as supernova. After the explosion what is left behind is a tiny object called black hole. The gravitational field on a black hole is so strong that it does not allow even light to escape. Thus, a black hole cannot be seen. However, astronomers locate black holes by the gravitational and other effects they have on nearby stars.

 

What is Atomic dock?

Atomic clock is a device for measuring time. It makes precise measurements of time. It makes use of the vibration of atoms or molecules, instead of quartz crystals or a coiled spring which are used in quartz and mechanical watches respectively, to measure time.

The most commonly used atoms and molecules in atomic clocks include caesium atoms, hydrogen atoms and molecules of ammonia gas. Atomic clocks based on rubidium atoms instead of caesium are now in use. Some atomic clocks gain or lose no more than a second in 200,000 years. These are used to keep time in laboratories and observatories. 

What is Allergy?

Allergy is a state of hypersensitivity acquired through the exposure to a particular substance, called allergen. Spores, pollen, cat’s hair and proteins of egg, milk, and fish are some common allergens. The most common allergen is the house-dust mite.

Usually only parts of the body which are exposed to allergens show signs of allergy in the form of rashes or weals. However, if an allergen gets into the blood stream, it can cause reactions almost anywhere in the body.

Practically all allergies are caused by an over-reaction of the body’s defence mechanism when white blood cells react with allergens considering them as dangerous infectious organisms, it leads to allergy. Under normal conditions, the white blood cells (lymphocytes) on coming in contact with foreign substances like bacteria, viruses and proteinaceous matter produce what are called antibodies. The antibodies combine with the foreign substance and neutralize it. But when an antibody is formed against a harmless protein it attaches itself to mast cells which contain chemical— histamine. When the particular protein enters the body again, histamine is released. Due to the action of histamine blood capillaries are dilated, their walls become leaky and fluid from the blood comes out in the nearby tissues and they swell. The characteristic redness and itching in an allergy is due to dilation of blood capillaries.

What is AIDS?

Acquired Immune Deficiency Syndrome (AIDS) is the most devastating and fatal disease of the 21st century. It is a viral disease caused by the Human Immune Deficiency Virus (HIV). What makes it different from other viruses is that, it strikes at the body’s own defence machinery (the immune system) that constantly fights the vast array of microbial enemies invading our bodies. The virus may remain dormant upto 10 years until some event activates it. On awakening, it disarms the immune system. With its main line of defence shattered, the body now falls easy prey to even the common infecting agents that it would otherwise ward off. The patient usually dies of these infections.

            HIV spreads from an infected person to a healthy person through body fluids. Sexual transmission of HIV is most common. Contaminated blood and blood products besides passage of the virus from infected mother to unborn baby are other ways by which the virus spreads.

What is Acid rain?

It is a phenomenon caused by industrial pollution. Natural rain always contains a small amount of dissolved carbon dioxide which makes it slightly acidic. But large-scale burning of coal or oil in industries, power plants and vehicles produce large amounts of gases such as sulphur dioxide, nitrogen oxides, etc., which are released into the atmosphere. These gases rise up with air currents and may be carried by prevailing winds many hundred of kilometres away from their source. Under favourable conditions they react with water vapour and oxygen in the atmosphere to produce sulphuric and nitric acids which eventually come down with rain, snow or fog. Compared to a pH of around 6 for normal rain, acid rains cause considerable damage to vegetation, trees and marine life. As the gases retry and acid rains fall in another damaging its flora and marine life, it has become a cause of concern to all countries. The countries worst affected by acid rains are southern Sweden, Norway, parts of central Europe and eastern regions of North America. Most European countries are therefore making efforts to reduce sulphur emissions by their industries and power plants.

 

How are Earthquakes measured?

The severity of an earthquake can be measured either by measuring its magnitude or intensity. Magnitude is a measure of the strength of an earthquake at its source. It is assessed on an 8-point scale called the Richter Scale. Devised in 1935, by an American geophysicist, Charles Richter, the scale assigns a number to an earthquake depending on its strength. The Richter magnitude is calculated by using information obtained from a seismograph — the instrument that records an earthquake’s ground motion.

Intensity is a measure of the local effect caused by an earthquake which varies according to distance from the source of the earthquake. The intensity is measured in the Mercalli scale, formulated originally by an Italian seismologist Giuseppe Mercalli. The scale was subsequently modified and is still used as the Modified Mercalli Intensity Scale (MM). It classifies earthquake into 12 categories ranging from 1 (not felt except by few) to 12 (total destruction).