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Category Modern Science

What is Galaxy?

GALAXIES

           Galaxies are gigantic collections of stars. The galaxy in which the Sun is situated, the Milky Way Galaxy, is a vast spiral of about 200 billion stars measuring about 100,000 light years across. There are billions more galaxies in the Universe, most of which are elliptical (oval) in shape. There are also others that have irregular shapes.

            The Milky Way has a bulge at its centre, the nucleus, where older red stars are concentrated. Four giant arms radiate out from the nucleus. These contain younger blue stars as well as areas of gas and dust – the raw material for the creation of new stars. The whole spiral spins at a speed of about 250 kilometres per second.

            The Milky Way Galaxy closely resembles the Andromeda Galaxy, which lies 2.25 million light years away. The Sun is situated on one of the spiral arms about halfway out from the nucleus. Here are mostly yellow and orange young-to-middle aged stars.

            The Horsehead Nebula is really a gigantic cloud of dust and gas that has taken on a familiar shape. It is one of many clouds in our Galaxy where stars start to form.

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What is Big Bang Theory?

BIG BANG

Many astronomers believe that the Universe began life in a single momentous event. This was an incredibly hot, dense explosion called the Big Bang, which took place about 15 billion years ago. During this explosion, all matter, energy, space – and time itself – were created.

In the first few millionths of a second, the particles that make up atoms, the building blocks of all matter, were formed. It took about 100,000 years for the first atoms, those of the gases hydrogen and helium, to come together. By this time, the searing heat of the Big Bang had cooled, space had expanded and the gases began to spread out. Gradually, however, gravity drew the gases together, leaving vast regions of empty space in between.

About a billion years after the Big Bang, the clouds of gas started to form into galaxies. Matter inside the galaxies went on clumping together until stars were created. Our own Sun was born in this way about 5 billion years ago. Its family of planets, including our Earth, was formed from the debris spinning round the infant Sun. With billions and billions of stars and planets forming in the same way across the Universe, it seems almost certain that life will have also evolved elsewhere. Will we on Earth one day make contact with these alien life-forms?

The expansion of the Universe is slowing down. Some astronomers think that gravity may eventually bring the expansion to a halt, then collapse all matter once more to a single point in a “Big Crunch”. Others believe that there is not enough material in the Universe to do this and that the Universe will carry on expanding forever.

Many scientists think that all matter in the Universe will eventually collide: the “Big Crunch”. Vast amounts of invisible “dark matter” in the Universe may exert sufficient gravity to halt its expansion and cause the galaxies to compress together.

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What is Universe?

UNIVERSE

Everything that we can think of and everything else that exists – all belong to the Universe. From grains of sand to tall buildings, from particles of dust to giant stars and planets, from microscopic bacteria to people – all are part of the Universe. It even includes empty space.

The Universe is unimaginably vast: billions upon billions of kilometres wide. Distances in the Universe are so great that we have to use a special measure to record them. This is a light year, or the distance that light, which moves at a speed of about 300,000 kilometres per second, travels in one year: about 9,460,528,405,000 kilometres. The nearest star to Earth (after the Sun), Proxima Centauri, is 4.2 light years away. The most distant objects we know in the Universe are more than 13 billion light years away from Earth.

Nearly all the matter in the Universe is contained in galaxies, enormous masses of stars, has and dust. There may be about 100 billion galaxies, each containing hundreds of billions of stars. Galaxies are grouped into giant “clouds” of galaxies, called superclusters. These are spread round the Universe like a net, made up of strings and knots. In between there are gigantic empty spaces.

The superclusters are, themselves, made up of smaller clusters of galaxies. One of these, a cluster of 30 galaxies or so, is called the Local Group. It contains the Milky Way Galaxy, the vast spiral of stars to which our own local star, the Sun, belongs.

Astronomers have discovered that all galaxies are rushing away from one another. This means that, a long time ago, they were once all close together. So the Universe had a definite beginning – and may have an end.

The Universe is composed of many galaxy superclusters, themselves made up of clusters of galaxies. One of these contains the Milky Way Galaxy, a spiral-shaped mass of about 200 billion stars, one of which is our own Sun, parent to a family of nine planets.

The third planet from the Sun is Earth, orbited by the Moon. Earth is the only world in the Universe where life is known to exist, but we may discover others one day.

It is possible that the Universe will carry on expanding forever. In this sequence, the Universe is created in an immense explosion called the Big Bang. It expands rapidly, with all the galaxies moving away from one another as the Universe inflates like a balloon.

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What should I know about Magnetism?

MAGNETISM

We cannot see or feel the force of magnetism. But it is all around us since the Earth is itself a giant magnet. A magnetic force affects mainly objects and substances that contain the metal iron. It pulls or attracts them. The force is present as a magnetic field around a magnet, which is itself usually made of iron.

Magnets of different sizes and shapes have hundreds of uses, from holding notes on a refrigerator to being vital parts in electrical generators, motors and loudspeakers.

A magnet does not always attract another magnet. Its magnetic force is strongest at two areas called its poles. These are different from each other and known as north and south poles. The north pole of one magnet attracts the south pole of another magnet. But it pushes away or repels the other magnet’s North Pole. The general rule is that unlike poles attract, like poles repel.

            A bar magnet is a strip of iron or steel in which the atoms are lined up in a certain way. Its magnetic force is strongest at its two ends or poles.

            The Earth has a magnetic field and two magnetic poles, north and south, almost as if it had a giant bar magnet inside.

            A magnetic compass is a needle-shaped magnet. Its poles are attracted to the Earth’s poles so it always turns to point north-south.

ELECTROMAGNETISM

Electricity and magnetism are two aspects of the same force, called the electromagnetic force. They are so closely linked that one can produce the other. A magnetic field moving near a wire causes electricity to flow in the wire. An electric current flowing in a wire makes a magnetic field around the wire. Twist the wire into a coil and it produces a stronger magnetic field. It can be turned on and off by switching the electricity on and off. This is an electromagnet. Electromagnetism is the basis of electric motors and generators.

            A maglev (magnetic levitation) train uses the pushing force between the like poles of magnets in the train and track. The force holds the wheel-less train above the track.

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Define Light and explain its main features?

LIGHT

Light is a kind of energy. It is the form of energy that our eyes can detect, enabling us to see. It is produced by very hot things – the Sun, fire and the tiny wire inside electric light-bulbs. Certain animals also have light-producing organs.

Light from the Sun is essential to life on Earth. Some creatures live off minerals in the ocean depths but these are exceptions. Most plants use sunlight to make their food. All plant-eating animals, together with other animals that eat plant-eaters, also therefore depend on sunlight.

Light rays can only travel in straight lines. If they strike an object which does not allow light to pass through it (an opaque object), a shadow is cast on the unlit side. Light can be reflected, however. Light reflected from objects allows us to see them. Light rays strike and bounce off a flat, shiny surface like a mirror at the same angle. This enables us to see our reflection.

THE SPEED OF LIGHT

When we switch on an electric light, it seems that the room is filled with light instantaneously. But light rays do take time to travel from their source. They travel extremely quickly: about 300,000 kilometres (or seven-and-a-half times around the world) per second in outer space. The speed of light is, in fact, the speed limit for the Universe: nothing can travel faster. Light waves are able to travel through empty space – a vacuum – whereas sound waves cannot. Light actually moves less quickly through air, water or glass than through empty space.

Because stars are very far from Earth – at least thousands of billions of kilometres – astronomers measure their distances in light years, the amount of time it takes for light to travel to us from them.

REFRACTION OF LIGHT

Light rays bend, or refract, when they pass through different transparent materials. This is because light travels at different speeds through different materials. At the boundary between two materials, for example, air and water, the light changes speed slightly and is refracted from its straight path. You can see this effect when looking at the bottom of swimming pool. It looks much shallower than it really is.

FOCUSING LIGHT

A lens, a shaped piece of glass or plastic, can bend light, either spreading it out or bringing it closer together. A convex lens, one that is thicker in the middle than at the edge, brings light rays together at a single point called a focus. The eye contains a natural convex lens which focuses an image on to the retina at the back of the eye. If you hold a convex lens so that the object you are looking at lies between the lens and the focus, the object will appear larger and further from the lens than it really is. A simple magnifying glass is a convex lens, and is useful for studying minute detail as, for example, on a postage stamp or a tiny insect or flower.

A concave lens is the opposite of a convex lens: it is thicker around the edge than in the middle. This kind of lens diverges (spreads out) light rays. It is used in glasses to correct short-sightedness.

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What should I know about Electricity?

 

ELECTRICITY

One of the most useful forms of energy in today’s world is electricity. It is transportable, which means it can be carried long distances by wires and cables. It is convertible, being changed into many other forms of energy, such as light from an electric light-bulb, and movement in an electric motor. It is also controllable. We can turn it on and off with a switch, or up and down with a knob. When a city suffers a power cut and falls still and silent, we realize how much we depend on electricity.

Electricity is the movement of electrons, the negative particles around the nucleus of an atom. Most metals, especially silver and copper, have electrons that can move easily from atom to atom, so they are good carriers or conductors of electricity. Electrons are pushed along the conductor by a battery or generator. But they flow only if they have a complete pathway of conductors called a circuit. Flowing electricity is known as electric current.

In substances such as rocks, wood, plastics, rubber and glass the electrons do not move easily. These materials prevent the flow of electricity and are known as insulators, but they may gain or lose electrons on their surface as a static electric charge.

            Static electricity is produced when electrons are separated from their atoms. On a comb it attracts bits of paper. In the sky it causes lightning!

            Electric current flows along a wire as electrons which detach from the outermost parts of their own atoms and jump or hop along to the next available atoms.

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Could you please tell something interesting about Colours and World of Colours?

COLOUR

One of the main features of light is colour. If light were just pure white, our whole world would be black and white and shades of grey. But white light is not pure. It is a mixture of all the colours of the rainbow which are known as the spectrum of light.

Colours exist because light is in the form of waves and not all the waves have the same wavelength. Some are slightly longer than others, and these we see as red. Light waves of medium wavelength appear to our eyes as green. We see the shortest light waves as violet. A leaf is green because its surface absorbs all the colours in white light except green, which it reflects into our eyes. A red flag absorbs all colours except red. Objects that reflect all colours are white.

The colour wheel shows how the different colours of light add up to make white light. When you spin the wheel the colours whirl around so fast that the eye cannot follow them. Inside the eye each colour merges with the others so the eye sees all the colours at once – and all colours of light added together make white light.

The different colours of light are seen when white light is split up using a prism, an angled block of transparent material such as clear glass or plastic. As the light waves pass into and then out of the prism they are bent or refracted. Longer waves of red light refract least. Shorter waves of violet light refract most. The other colours spread out between. A raindrop works as a natural prism. Millions of raindrops split sunlight and form a rainbow in the sky.

ADDING COLOURS

We see colours in books and on screens such as the television, in different ways. A television or computer screen has thousands of tiny dots that glow and give out light. These dots have actually only three colours – red, green and blue. These colours are known as the primary colours of light. Added to each other in different combinations and brightness they can make any other colour. For example, red and green together make the colour yellow. Red and blue produce the pinky colour known as magenta. Blue and green form cyan, a type of turquoise. The three primary colours of red, blue and green added together make white light.

On the screen of a computer or TV the dots are arranged in groups known as pixels. The different colours of dots flash on and off in different combinations and shine with different brightnesses. From a distance, the eye cannot see the individual dots. They merge to produce larger areas of colour. When all the red dots on an area of the screen shine, that area looks red. When all three colours of dots in an area of the screen shine brightly, that area looks white. Also the dots flash on and off many times each second, again too fast for the eye to follow. So they merge together in time to produce multi-coloured, moving pictures.

SUBTRACTING COLOURS

Coloured pictures in a book are made like those on a screen, using tiny coloured dots that merge together. The dots are inks made with coloured substances called pigments. There are three primary pigment colours – yellow, magenta and cyan. They work in the opposite way to light colours. They do not add together, but take away or subtract. A yellow dot takes away all colours of light except yellow which it reflects. The other two dots do the same for their colours. By taking away individual colours, the dots merge to produce areas of other colours. All three dots together make black.

            The wolf’s mask is realistic and frightening. Yet it is printed using tiny dots of only three colours. They can be separated as magenta, cyan and yellow. To save on coloured inks some parts of the page, like these words, are printed with ready-made black ink.

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How does Transfer of Heat take Place?

HEAT MOVES

Heat can move around and between objects in three main ways. One is conduction, when heat energy passes between two objects in physical contact. When you touch an object to see how warm it is, you receive some of its heat by conduction. A second way is by convection. This only happens in liquids and gases. As some of the atoms or molecules receive heat energy and become warm they spread out more. The heated part of the liquid or solid is now less dense than its cooler surroundings so it rises or floats. As it rises, it carries its heat energy in the form of convection current. You can feel this as warm air rising from a central heating radiator.

The third way that heat moves is by radiation. It is in the form of infrared waves which are part of a whole range of waves, including radio waves, light and X-rays, known as the electromagnetic spectrum. Conduction and convection both need matter to transfer heat. Radiation does not. Infrared waves can pass through space, which is how the Sun’s heat reaches Earth.

Like light waves, infrared waves reflect from light-coloured or shiny surfaces. On a hot day, light-coloured clothes reflect the Sun’s warmth and keep you cooler than dark clothing, which absorbs the warmth. Substances that slow down conduction and convection, such as wood, plastic and glass fibre, are called thermal insulators. Layers of fat, or blubber in a whale, are good insulators.

The faster an aircraft goes, the greater the heat from friction with air. Very fast planes like the X-15 rocket have special heat-radiating paint that gives out heat as fast as possible, to prevent the metal skin of the plane melting at high speed.

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How would you distinguish between Pitch and Volume of Sound?

PITCH AND VOLUME

Sound has two important features. One is pitch. A low-pitched sound is deep, like a roll of thunder or a booming big drum. A high-pitched sound is shrill, like a snake’s hiss or the tinkle of a triangle. Pitch depends on the frequency of sound waves – the number of waves per second. High-pitched sounds have high frequencies.

Some sounds are so high-pitched that our ears cannot detect them. They are known as ultrasounds. Many animals, like dogs and bats, can hear ultrasounds.

The second important feature of sound is its loudness or volume. Some sounds are so quiet that we can only just hear them, like a ticking watch or the rustling of leaves. Other sounds are so loud, like the roar of engines or the powerful music in a disco, that they may damage the ears. Sound volume, or intensity, is measured in units called decibels (dB). Sounds of more than 80-90 decibels can damage our hearing.

            An ultrasound scanner beams very high-pitched sound waves into the body. The echoes are analyzed by a computer to form an image, the baby in the womb.

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How would you explain Heat?

HEAT

How warm is the weather today? It may be cold and wintry or hot and summery. Heat is a vital part of our lives. We need to keep our bodies comfortably warm with clothing, especially in cold conditions. If body temperature falls from its normal 37°C to below about 30°C, fatal hypothermia may set in.

We cook our food with heat using gas or electricity. Countless machines and industrial processes use heat, from making pottery or a photocopy to a steelworks or power station. Heat is also given off as a waste form of energy by many processes. In a power station most of the heat is used to generate electricity, but some is released as clouds of steam from huge cooling towers.

Heat is a type of energy – the vibrations of atoms and molecules. The more an atom moves or vibrates, the more heat or thermal energy it has. In a solid, the atoms have fixed central positions but each atom vibrates slightly about its central position, like a ball tied to a nail by elastic. Heat the solid and the atoms vibrate more. When they have enough vibrations, the atoms break from their fixed positions (the “elastic” snaps), and they move about at random. The solid has melted into a liquid. Heat it more and the atoms fly further apart. The liquid becomes a gas.

 TEMPERATURE

Cold is not the presence of something that opposes heat, but simply the lack of heat. Temperature is not the same as heat. Heat is a form of energy, while temperature is a measure of how much heat energy a substance or object contains. A slice of apple pie at 40°C contains more heat energy than a same-sized slice of the same pie at 30°C. We can judge its temperature quite accurately when we touch the slice with our skin, and especially with our fingertips or lips. But this judgement is only safe within a certain range. Temperatures greater than about 50°C or lower than about -10°C cause pain and may damage the skin. We measure temperatures accurately using devices called thermometers.

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