Current Affairs UPSC

Electric Current and Magnetism

Electric Current and Magnetism 1. Electric Current and Circuit

Electric current is expressed by the amount of charge flowing through a particular area in unit time. In other words, it is the rate of flow of electric charges.
In circuits using metallic wires, electrons constitute the flow of charges.
Electric current was considered to be the flow of positive charges and the direction of flow of positive charges was taken to be the direction of electric current.
The direction of electric current is taken as opposite to the direction of the flow of electrons, which are negative charges.
The SI unit of electric charge is coulomb (C), which is equivalent to the charge contained in nearly \[6\times {{10}^{18}}\] electrons. (We know that an electron possesses a negative charge of \[1.6\times {{10}^{-19}}\,\,C)\].
The electric current is expressed by a unit called ampere (A). One ampere is constituted by the flow of one coulomb of charge per second.
An instrument called ammeter measures electric current in a circuit. It is always connected in series in a circuit through which the current is to be measured.

2. Electric Potential and Potential Difference

What makes the electric charge to flow? The electrons move only if there is a difference of electric pressure - called the potential difference - along the conductor. This difference of potential may be produced by a battery, consisting of one or more electric cells.
The chemical action within a cell generates the potential difference across the terminals of the cell, even when no current is drawn from it.
When the cell is connected to a conducting circuit element, the potential difference sets the charges in motion in the conductor and produces an electric current. In order to maintain the current in a given electric circuit, the cell has to expend its chemical energy stored in it.
We define the electric potential difference between two points in an electric circuit carrying some current as the work done to move a unit charge from one point to the other.
The SI unit of electric potential difference is volt (V), named after Alessandro Volta (1745-1827), an Italian physicist. One volt is the potential difference between two points in a current carrying conductor when 1 joule of work is done to move a charge of 1 coulomb from one point to the other.

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Catgeory: UPSC

NCERT Extracts - Electromagnetic Waves

Electromagnetic Waves 1. Radio Waves

Radio waves are produced by the accelerated motion of charges in conducting wires.
They are used in radio and television communication systems.
They are generally in the frequency range from 500 kHz to about 1000 MHz. The AM (amplitude modulated) band is from 530 kHz to 1710 kHz. Higher frequencies upto 54 MHz are used for short wave bands.
TV waves range from 54 MHz to 890 MHz. The FM (frequency modulated) radio band extends from 88 MHz to 108 MHz. Cellular phones use radio waves to transmit voice communication in the ultrahigh frequency (UHF) band.

2. Microwaves Microwaves (short-wavelength radio waves), with frequencies in the gigahertz (GHz) range, are produced by special vacuum tubes (called klystrons, magnetrons and Gunn diodes).

Due to their short wavelengths, they are suitable for the radar systems used in aircraft navigation. Radar also provides the basis for the speed guns used to time fast balls, tennisserves, and automobiles.
Microwave ovens are an interesting domestic application of these waves. In such ovens, the frequency of the microwaves is selected to match the resonant frequency of water molecules so that energy from the waves is transferred efficiently to the kinetic energy of the molecules. This raises the temperature of any food containing water.

3. Microwave Oven

The spectrum of electromagnetic radiation contains a part known as microwaves. These waves have frequency and energy smaller than visible light and wavelength larger than it. What is the principle of a microwave oven and how does it work?
Our objective is to cook food or warm it up. All food items such as fruit, vegetables, meat, cereals, etc., contain water as a constituent. Now, what does it mean when we say that more...

Catgeory: UPSC

Communication Systems

Communication Systems 1. Some Major Milestones in the History of Communication

In 1835 Invention of telegraph by Samuel F.B. Morse and Sir Charles Wheatstone. It resulted in tremendous growth of messages through post offices and reduced physical travel of messengers considerably.
In 1876 Telephone is invented by Alexander Graham Bell and Antonio Meucci Perhaps the most widely used means of communication in the history of mankind.
In 1895 Jagadis Chandra Bose and Guglieimo Marconi demonstrated wireless telegraphy. It meant a giant leap - from an era of communication using wires to communicating without using wires, (wireless)
In 1936 Television broadcast (John Logi Baird) First television broadcast by BBC.
In 1955 First radio FAX transmitted across continent. (Alexander Bain) The idea of FAX transmission was patented by Alexander Bain in 1843.
In 1968 ARPANET - the first internet came into existence (J.C.R. Licklider) ARPANET was a project undertaken by the U.S. defence department. It allowed file transfer from one computer to another connected to the network.
In 1975 Fiber optics developed at Bell Laboratories Fiber optical systems are superior and more economical compared to traditional communication systems.
In 1989-91 Tim Bemers-Lee invented the World Wide Web. WWW may be regarded as the mammoth encyclopedia of knowledge accessible to everyone round the clock throughout the year.

2. Basic Terminology used in Electronic Communication Systems

Any device that converts one form of energy into another can be termed as a transducer.
Information converted in electrical form and suitable for transmission is called a signal.
Signals can be either analog or digital. Analog signals are continuous variations of voltage or current. They are essentially single-valued functions of time. Sine wave is a fundamental analog signal. All other analog signals can be fully understood in terms of their sine wave components. Sound and picture signals in TV are analog in nature.
Digital signals are those which can take only discrete stepwise values. Binary system that is extensively used in digital electronics employs just two levels of a signal. \['0'\] Corresponds to a low level and \['1'\] corresponds to a high level of voltage/current.
There are several coding schemes useful for digital communication. They employ suitable combinations of number systems such as the binary coded decimal (BCD). American Standard Code for Information Interchange (ASCII) is a universally popular digital code to represent numbers, letters and certain characters.

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Catgeory: UPSC

NCERT Extracts - Miscellaneous Physics

Miscellaneous : Physics 1. Units and Measurement

Measurement of any physical quantity involves comparison with a certain basic, arbitrarily chosen, internationally accepted reference standard called unit.
The units for the fundamental or base quantities are called fundamental or base units. The units of all other physical quantities can be expressed as combinations of the base units. Such units obtained for the derived quantities are called derived units. A complete set of these units, both the base units and derived units, is known as the system of units.
In earlier time scientists of different countries were using different systems of units for measurement. Three such systems, the CGS, the FPS (or British) system and the MKS system were in use extensively till recently.
The base units for length, mass and time in these systems were as follows :
In CGS system they were centimetre, gram and second respectively.
In FPS system they were foot, pound and second respectively.
In MKS system they were metre, kilogram and second respectively.
The system of units which is at present internationally accepted for measurement is the Systeme Internationale d. Unites (French for International System of Units), abbreviated as SI. The SI, with standard scheme of symbols, units and abbreviations, was developed and recommended by General Conference on Weights and Measures in 1971 for international usage in scientific, technical, industrial and commercial work. Because SI units used decimal system, conversions within the system are quite simple and convenient.
In SI, there are seven base units besides these there are two more units.
SI Base Quantities and Units :
Length - metre (m): The metre is the length of the path travelled by light in vacuum during a time interval of \[1/299,792,458\] of a second. (1983)
Mass - kilogram (kg): The kilogram is equal to the mass of the international prototype of the kilogram (a platinum-iridium alloy cylinder) kept at international Bureau of Weights and Measures, at Sevres, near Paris, France. (1889)
Time - Second (s): The second is the duration of \[9,192,631,770\]periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom. (1967)
Electric current - ampere (A): The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 metre apart in vacuum, would produce between these conductors a force equal to \[2\times {{10}^{-7}}\] newton per metre of length. (1948)
Thermo Dynamic Temperature - kelvin (K) : The kelvin, is the fraction 1/273.16 of the thermodynamic more...

Catgeory: UPSC

NCERT Extracts - Environmental Issues

Environmental Issues 1. Greenhouse Effect

Greenhouse gases absorb long wave (infrared) radiation from the earth, and emit it again towards the earth. The cycle continues till the earth's surface has no long wave radiation to emit.
The greenhouse effect is a naturally occurring phenomenon that is responsible for heating of Earth's surface and atmosphere.
It is surprising that without greenhouse effect the average temperature at surface of Earth would have been a chilly \[-18{}^\circ C\] rather than the present average of \[15{}^\circ C\].
In order to understand the greenhouse effect, it is necessary to know the fate of the energy of sunlight that reaches the outermost atmosphere.
Clouds and gases reflect about one-fourth of the incoming solar radiation, and absorb some of it but almost half of incoming solar radiation falls on Earth's surface heating it, while a small proportion is reflected back. Earth's surface re-emits heat in the form of infrared radiation but part of this does not escape into space as atmospheric gases (e.g., carbon dioxide, methane, etc.) absorb a major fraction of it.
The molecules of these gases radiate heat energy, and a major part of which again comes to Earth's surface, thus heating it up once again. This cycle is repeated many a times. The above-mentioned gases - carbon dioxide and methane - are corn monly known as greenhouse gases because they are responsible for the greenhouse effect.
Increase in the level of greenhouse gases has led to considerable heating of Earth leading to global warming. During the past century, the temperature of Earth has increased by \[0.6{}^\circ C\], most of it during the last three decades.

2. Ozone Depletion

Bad ozone, formed in the lower atmosphere (troposphere) that harms plants and animals. There is 'good' ozone also; this ozone is found in the upper part of the atmosphere called the stratosphere, and it acts as a shield absorbing ultraviolet radiation from the sun.
UV rays are highly injurious to living organisms since DNA and proteins of living organisms preferentially absorb UV rays, and its high energy breaks the chemical bonds within these molecules.
The thickness of the ozone in a column of air from the ground to the top of the atmosphere is measured in terms of Dobson units (DU).
Ozone gas is continuously formed by the action of UV rays on molecular oxygen, and also degraded into more...

Catgeory: UPSC

Ecology

Ramdeo Misra is revered as the Father of Ecology in India. Due to his efforts, the Government of India established the National Committee for Environmental Planning and Coordination (1972) which, in later years, paved the way for the establishment of the Ministry of Environment and Forests (1984).

1. Biotic and Abiotic Factors

The key elements that lead to so much variation in the physical and chemical conditions of different habitats are temperature, water, light and soil. Temperature is the most ecologically relevant environmental factor. The average temperature on land varies seasonally.
We can readily appreciate the significance of temperature to living organisms when we realise that it affects the kinetics of enzymes and through it the basal metabolism, activity and other physiological functions of the organism.
A few organisms can tolerate and thrive in a wide range of temperatures.
Next to temperature, water is the most important factor influencing the life of organisms. In fact, life on earth originated in water and is unsustainable without water.
Plants produce food through photosynthesis, a process which is only possible when sunlight is available as a source of energy, we can quickly understand the importance of light for living organisms, particularly autotrophs.
Many species of small plants (herbs and shrubs) growing in forests are adapted to photosynthesise optimally under very low light conditions because they are constantly overshadowed by tall, canopied trees.
Many plants are also dependent on sunlight to meet their photoperiodic requirement for flowering.
For many animals too, light is important in that they use the diurnal and seasonal variations in light intensity and duration (photoperiod) as cues for timing their foraging, reproductive and migratory activities.
The availability of light on land is closely linked with that of temperature since the sun is the source for both. But, deep (\[>\]500 m) in the oceans, the environment is perpetually dark and its inhabitants are not aware of the existence of a celestial source of energ) called Sun. What, then is their source of energy?
The spectral quality of solar radiation is also important for life. The UV component of the spectrum is harmful to many organisms while not all the colour components of the visible spectrum are available for marine plants living at different depths of the ocean.

2. Responses to Abiotic Factors

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Catgeory: UPSC

Inheritance and Development

Inheritance and Development 1. Mutation

Inheritance is the process by which characters are passed on from parent to progeny; it is the basis of heredity. Variation is the degree by which progeny differ from their parents.
Mutation is a phenomenon which results in alteration of DNA sequences and consequently results in changes in the genotype and the phenotype of an organism. In addition to recombination, mutation is another phenomenon that leads to variation in DNA.
One DNA helix runs continuously from one end to the other in each chromatid, in a highly supercoiled form. Therefore loss (deletions) or gain (insertion/duplication) of a segment of DNA, result in alteration in chromosomes. Since genes are known to be located on chromosomes, alteration in chromosomes results in abnormalities or aberrations. Chromosomal aberrations are commonly observed in cancer cells.
In addition to the above, mutation also arise due to change in a single base pair of DNA. This is known as point mutation. A classical example of such a mutation is sickle cell anemia. Deletions and insertions of base pairs of DNA, causes frame-shift mutations.
There are many chemical and physical factors that induce mutations.

2. Genetic Disorders

Broadly, genetic disorders may be grouped into two categories - Mendelian disorders and Chromosomal disorders. Mendelian disorders are mainly determined by alteration or mutation in the single gene. These disorders are transmitted to the offspring.
The pattern of inheritance of such Mendelian disorders can be traced in a family by the pedigree analysis. Most common and prevalent Mendelian disorders are Haemophilia, Cystic fibrosis, Sickle-cell anaemia, Colour blindness, Phenylketonuria, Thalassemia, etc.
It is important to mention here that such Mendelian disorders may be dominant or recessive. By pedigree analysis one can easily understand whether the trait in question is dominant or recessive.
Similarly, the trait may also be linked to the sex chromosome as in case of haemophilia. It is evident that this X-linked recessive trait shows transmission from carrier female to male progeny.

Haemophilia
This sex linked recessive disease, which shows its transmission from unaffected carrier female to some of the male progeny has been widely studied.
In this disease, a single protein that is a part of the cascade of proteins involved in the clotting of blood is affected. Due to this, in an affected individual a simple cut will result in non-stop bleeding.
The heterozygous female more...

Catgeory: UPSC

Biodiversity and Conservation

Biodiversity and Conservation 1. Biodiversity

Biodiversity is the term popularised by the sociobiologist Edward Wilson to describe the combined diversity at all the levels of biological organisation. The most important of them are:
Genetic diversity: A single species might show high diversity at the genetic level over its distributional range. The genetic variation shown by the medicinal plant Rauwolfia vomitoria growing in different Himalayan ranges might be in terms of the potency and concentration of the active chemical (reserpine) that the plant produces. India has more than 50,000 genetically different strains of rice, and 1,000 varieties of mango.
Species diversity: The diversity at the species level. For example, the Western Ghats have a greater amphibian species diversity than the Eastern Ghats.
Ecological diversity: At the ecosystem level, India, for instance, with its deserts, rain forests, mangroves, coral reefs, wetlands, estuaries, and alpine meadows has a greater ecosystem diversity than a Scandinavian country like Norway.
It has taken millions of years of evolution, to accumulate this rich diversity in nature, but we could lose all that wealth in less than two centuries if the present rates of species losses continue.

2. Species on the Earth and in India

More than 70 per cent of all the species recorded are animals, while plants (including algae, fungi, bryophytes, gymnosperms and angiosperms) comprise no more than 22 per cent of the total.
Among animals, insects are the most species-rich taxonomic group, making up more than 70 per cent of the total. That means, out of every 10 animals on this planet, 7 are insects. Again, how do we explain this enormous diversification of insects?
The number of fungi species in the world is more than the combined total of the species of fishes, amphibians, reptiles and mammals.
It should be noted that these estimates do not give any figures for prokaryotes. Biologists are not sure about how many prokaryotic species there might be. The problem is that conventional taxonomic methods are not suitable for identifying microbial species and many species are simply not culturable under laboratory conditions. If we accept biochemical or molecular criteria for delineating species for this group, then their diversity alone might run into millions.
Although India has only per cent of the world's land area, its share of the global species diversity is an impressive per cent. That is what makes our country one of more...

Catgeory: UPSC

The Human Eye and the Light

The Human Eye and the Light 1. The Human Eye

The human eye is one of the most valuable and sensitive sense organs. It enables us to see the wonderful world and the colours around us.
The human eye is like a camera. Its lens system forms an image on a light-sensitive screen called the retina.
Light enters the eye through a thin membrane called the cornea. It forms the transparent bulge on the front surface of the eyeball. The eyeball is approximately spherical in shape with a diameter of about
Most of the refraction for the light rays entering the eye occurs at the outer surface of the cornea.
The crystalline lens merely provides the finer adjustment of focal length required to focus obiects at different distances on the retina.
A structure called iris behind the cornea. Iris is a dark muscular diaphragm that controls the size of the pupil. The pupil regulates and controls the amount of light entering the eye.
The eye lens forms an inverted real image of the object on the retina. The retina is a delicate membrane having enormous number of light-sensitive cells. The light-sensitive cells get activated upon illumination and generate electrical signals. These signals are sent to the brain via the optic nerves.
The brain interprets these signals, and finally, processes the information so that we perceive objects as they are.
Damage to or malfunction of any part of the visual system can lead to significant loss of visual functioning. For example, if any of the structures involved in the transmission of light, like the cornea, pupil, eye lens, aqueous humour and vitreous humour or those responsible for conversion of light to electrical impulse, like the retina or even the optic nerve that transmits these impulses to the brain, is damaged, it will result in visual impairment.
We are not able to see objects clearly for some time when we enter from bright light to a room with dim light. After sometime, however, we may be able to see things m the dim-lit room. The pupil of an eye acts like a variable aperture whose size can be varied with the help of the iris.
When the light is very bright, the iris contracts the pupil to allow less light to enter the eye. However, in dim light the iris expands the pupil to allow more light to enter the eye. Thus, the pupil opens completely through the relaxation of the iris.

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Catgeory: UPSC

The Living Organisms and their Surroundings

The Living Organisms and their Surroundings 1. Habitat and Adaptation

Camels have long legs which help to keep their bodies away from the heat of the sand.They excrete small amount of urine, their dung is dry and they do not sweat. Since camels lose very little water from their bodies, they can live for many days without water.
There are so many kinds of fish, but they all have something common about their shape. All the ones have the streamlined shape. This shape helps them move inside water. Fish have slippery scales on their bodies. These scales protect the fish and also help in easy movement through water. Fish have flat fins and tails that help them to change directions and keep their body balance in water. Gills present in the fish help them to use oxygen dissolved in water.
The presence of specific features or certain habits, which enable a plant or an animal to live in its surroundings, is called adaptation.
The surroundings where organisms live is called a habitat.
The living things such as plants and animals, in a habitat, are its biotic components. Various non-living things such as rocks, soil, air and water in the habitat constitute its abiotic components. Sunlight and heat also form abiotic components of the habitat.
Desert animals like rats and snakes, which do not have the long legs that the camel has. To stay away from the intense heat during the day, they stay in burrows deep in the sand. These animals come out only during the night, when it is cooler.
Desert plants lose very little water through transpiration. The leaves in desert plants are absent very small, or they are present in the shape of spines. This helps in reducing loss of waier from the leaves through transpiration e.g. The leaf-like structure in a cactus is, in fact, its stem.
Photosynthesis in these plants is usually carried out by the stems. The stem is also covered with a thick waxy layer, which helps to retain water. Most desert plants have roots that go very deep into the soil for absorbing water.
In a mountain region trees are normally cone shaped and have sloping branches. The leaves of some of these trees are needle-like. This helps the rainwater and snow to slide off easily.
Animals living in the mountain regions are also adapted to the conditions there. They have thick skin or fur to protect them from cold. For example, yaks have long hair to keep them warm. Snow leopard has thick fur on its body including feet and toes. This protects its more...

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