OUR UNIVERSE

1. THE BIG BANG

We take the world as we see it around us as the given, as if it was always there. But science tells us strange, wondrous and fascinating things about the world. The world as we know it, not just the earth and the solar system – but the whole universe was at a point 1400 crore years back.

Think! What an imagination it needs to visualize that! The whole gigantic universe with its billions (100 curves) of galaxies, each containing billions of stars wasn’t even there as it is now but was concentrated at a point, called by the scientists, the singularity.

Now this is a strange fact, probably the strangest of all facts. So we obviously need to ask: why. Why was the whole universe at a point?

The answer is incredible and it lies in just understanding deeply the reality of an almost omnipotent force that governs the universe. That force is the force of gravity and it is universal. Let us proceed how to get a deep, real understanding of gravity. Since childhood we have observed things falling from a height if left free. We have observed it so many times that we take it for granted. We do not system, it, wonder about it, even feel it.

Yet, think!

Why should things fall? After all, we are not pushing it down and there is no contact between the earth, and the falling body. Isn’t it strange – this action at a distance. You leave a body and it moves towards the earth. The earth is a sphere and all objects get attracted to the centre of the earth and participates in the motion of the earth. Our atmosphere, the air we have, our oceans, everything is held onto the earth along the whole of it’s surface and circumference.

The ancients wondered about this gravity on earth. But later from 13th century onwards people began looking at the heavens too and began wondering and also, additionally, began tracing the motions of the planets the sun and the moon. They collected lot of data and bit by bit they came to understand that it was not the sun that moved around a stationary earth (as the ancients had assumed) but it was the earth (and other planets) that moved around the sun.

This whole inquiry culminated in the Kepler’s laws of motion of planets which describes the regular, uniform behavior of planets round the sun (it was not random or accidental).

Then Newton began a serious, deep inquiry in to this matter. Remember it was very early. Nothing was really clear. The heavenly motions of planets had been traced out. People observed the things falling on earth but no connection was made. It was almost as if, then the heavens were different from the earth. Newton’s incredible daring and genius lay in linking it. As legend has it, he observed an apple falling and suddenly he got this great thought. Are the motions of the apple falling and the moon falling the same? The moon ‘fall’ in the sense that if it did not fall towards the earth it would go off the straight line. It was already understood that the moon’s motion and even the planets motions were a result of two motions – one horizontally and other perpendicular and vertical towards the sun.

These two motions combined to give the almost circular motion of the moon and planets. (All circular motion is a combination of two such motions.)

Well, Newton thought about this and he suddenly got it!

He understood, in a flash of genius, that actually every mass attracts every other mass!

He got the mathematics of it also the power of attraction is directly proportional to both masses and inversely proportional to the square of the distance between them. This simply means the more any, or both of the masses, more the attractive force. Greater the distance, lesser is the attractive force. Also the reduction is as the square of the distance i.e. if distance is doubled the force is reduced 4 times, if the distance is tripled (made 3 times), the force is reduced by (3x3) 9 times!

This equation fitted with Kepler’s equation and Newton made the heavens and the earth one!

Just think! What a law Newton’s universal law of gravitation really is!

Every mass attracts every other mass in the universe and earth is merely one such mass and this law holds true for all the masses of the universe. Even 2 objects on earth actually get attracted. The reason we do not see a visible movement is because the attractive force of gravity is very weak. Unless the masses are of big size, there is not much attraction. This is the reason why things fall slowly on the moon – the mass of moon is 1/6th of the earth and hence the gravitational force (as it is called) is also 1/6the! That is why we see that wondrous (slow motion like) falling of things on the moon.

In space, things do not fall at all! They just ‘hang’ where they are! This is because the object is too far from any big size object to feel any attraction. So it just remains where it is! Isn’t this a wonder!!

Newton had literally swept the space clean and unlocked one of the deepest mysteries of the universe. Now, still a major, in fact, obvious question remained. If every mass attracts every other mass, how can the world as we see it – earth, planets, stars be at all? Should they not actually be together, this whole universe, at one place?

This was seriously asked, in the 1900s and no answer existed. The question, however, remained. Then in the 1900s another strange fact came into light.

Scientists discovered that the universe, as a whole was expanding. Every object was going away from every object. They came to know this by a phenomenon called Doppler effect. Doppler effect is very common with respect to sound. Sound consists of waves and if a body making sound is approaching you, the waves crowd together and the number of waves per second, that is the frequency increases. The opposite happens when the body making the sound is going away from you. Here, the waves are more stretched out and the number of waves per second is less. That is the frequency is decreased. Now the interesting thing is that light too is a wave and the same thing has been tested to happened to light too. A body emitting light, if its going away from you would change its frequency towards the red. This is called the red shift. If the body emitting

light is coming towards you, the n the frequency is increased and the light shifts towards the blue. This is called the blue shift. Now it was observe through countless experiments, that whenever you observe an object in the heavens, a star or a galaxy that is emitting light, it is shifting towards the red! This means that everything is going from away you. This actually means that the whole universe is expanding and everything is going away from each other.

It is then that they understood why the universe is not coming together due to gravity. Actually expansion of the universe was countering gravity. If the universe is expanding, then the whole universe must have been at a point and there must have been a big bang. This is how the scientist came to the conclusion that the whole universe was at a point and then the big bang happened.

After the big bang within moments, hydrogen atoms were created and began filling the whole space from these hydrogen atoms were born the stars, the galaxies and the solar system. How this happened will be understood in the following sections.


2. FORMATION OF GALAXIES


We have learnt that the whole matter of the universe was at one point 14 billion years back and that there was a big bang.

After the big bang what happened?

The simplest atoms of hydrogen gas were formed and they filled the blank space after millions of years. Because of the big bang, the expansion continued in all directions. But in many areas the cloud of hydrogen gas were a little closer and due to gravity formed huge regions of concentrated hydrogen gas. These are the galaxies!

Even in these regions, in some areas hydrogen gas got even further closer and formed stars. When the stars died they burst and again spread out. All the stars in each galaxy also attracted each other and formed systems of stars. The galaxies themselves attracted other galaxies, again due to gravity. Sometimes they push into each other giving various shapes of galaxies and also complicated motions. These motions continue to this day.

So you see its not just all galaxies expanding away from each other. They move themselves too and the motions never stop!

We live in a galaxy called the milky way galaxy. Sometimes in a clear night, we see a white spread in the sky, that is the milky way galaxy. Our milky way galaxy contains our Sun as just one of the billions of stars. So you can imagine how huge just the milky way galaxy is! Now there are billions of such galaxies! So the size of universe is literally unimaginable! We can only feel it.

3. BIRTH OF STARS

We have learnt already that after the big bang, hydrogen gas filled the emptiness of space. We also learnt that in some huge regions galaxies are formed which are nothing but masses of hydrogen gas collecting together. In these galaxies are formed stars.

In some regions a little bit of hydrogen gas comes together in the form of clumps and this begins a process that goes on. The clump starts attractive, due to gravity the surrounding hydrogen gas. It becomes bigger and bigger. The more big it becomes the more powerfully it attracts all the hydrogen gas arrounded towards its centre!

This process goes on and on. The clump becomes bigger and bigger and bigger and attracts more and more powerfully the hydroges gas around it. Now this whole attraction towards it centre creates a very huge pressure. Now pressure is related to temperature, to the producing of heat. If you rub your hands hard, it becomes very hot. Wherever there is pressure there is heat. Heat is nothing more then the internal jiggling and wiggling of atoms/molecules inside matter. More the pressure more the temperature. If the pressure becomes huge the temperature too rises to a very high level. This is what happens inside the clump which becomes very huge. There is a high temperature of lakhs of degrees created inside the star. This removes electrons from the atoms of hydrogen. An atom contains proton and neutrons in its central nucleus and electrons orbit around it. Hydrogen atom contains one proton, one neutron and one electron. When the electrons are removed due to the high heat, a process called nuclear fusion reaction take place.

Fusion means joining together. In normal circumstances a hydrogen nucleus cannot join with another hydrogen nucleus. This is because protons are positively charged and if two nucleus of hydrogen come close together the proton in one hydrogen atom would repel the proton in the other hydrogen atom (two positives charge repel each other).

But when the temperature is extremely high the repulsion is overcome and the two nuclei actually join together, fuse together and becomes another nucleus! This nucleus contains two protons and is the element helium.

So in the star, hydrogen starts becoming helium. In this process a strange thing happens. Mass is lost and converted into huge amounts of energy (by the formula of E=mc2). This creates an outward force from the centre of the star. But there is another force too. Because the star is so huge there is an internal gravitational attraction towards the centre also.

These two forces the constant creation of nuclear energy outwards and the inner sucking force of gravitation balance each other and the star is born!

How long does this last? Obviously till the hydrogen is used up in the Star. What happens when the hydrogen is used up? The star begins the process of death. What is this process?

What are all the things that happen when hydrogen is used up?

We will see that in the next section.


4. DEATH OF STARS


When the hydrogen gas is completely used up to make helium, two things can happen depending on the size of the star.

The process of death of a small sized star (like our Sun):

When the hydrogen is used up in a small sized star, the outward force of nuclear energy created stops. Then what happens is the centre of the star shrinks but the outward covering of the star sort of floats up like a huge flare. So the star suddenly becomes big and redder. This is a red giant. Inside helium now starts a process of nuclear fusion reaction again and becomes lithium. But this does not last long as the helium is used up very quickly. After this again the outward force of nuclear energy stops and the inside of the star shrinks and the outside flares up as a second red giant. For a small size star, this is all. The red giant cools. The star becomes very small, the size of the earth but more dense. This is the white dwarf and a kind of ending of the star. The Sun being a medium sized star will go through all these processes. After 4 to 5 billion years i.e. the Sun would die.

The process of death of a big sized star:

For a large sized star too the hydrogen gets used up and there is an outward flare, this is a huge blast and it is called a Supernova. But here is the difference, inside the star the helium becomes lithium, the lithium becomes the next element and so on and there is a series of red giants. The second difference is what happens when the series ends.

Remember, if the star is huge the inner sucking gravitational force would be very huge. This huge force breaks up matter also and the star instead of becoming a white dwarf becomes a neutron star. The star contains only neutrons.

If the star is even more huge we don’t even get a neutron star it ends up as a black hole where all the matter vanishes due to the huge gravitational force directed towards the centre. Gravity here completely makes the matter vanish and light get sucked into the black hole. So this is the way stars are born and star die continuously in the universe.

In this whole universe we on earth are only a speak and in a way insignificant!


5. FORMATION OF THE SOLAR SYSTEM


There are two main theories that explain the formation of the solar system (the sun, planets and asteroids). But the theory most widely accepted by all scientists today is the nebula theory. Long back, there was a huge mass of gas, dust and ice in the region which is now the solar system. At that time, probably due to a supernova (exploding star), this mass was disturbed. A disturbance in the universe is dangerous because if masses gets close together gravity starts acting and collapses the mass.

This is what happen the mass got closer together due to the explosion and the mass also started spinning. As they got more and more close while spinning the spinning became faster. Slowly over a period of time the whole shapeless spinning gas started becoming orderly, uniform and flat. Now this whole thing exactly like a frisbee or cake spinning very fast round and round. Slowly in certain areas this gas got closer together again due to gravity and slowly formed larger bodies called planetesimals. Even more matter flying around stuck to these planetesimals and slowly over a long period of time the solar system as we know today was formed that is the sun at the centre and the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

The question now remains as to how the sun was formed at the centre. At the centre the pressure was very high and temperature rose to lakhs of degrees and the process of formation of star started i.e. hydrogen becoming helium and releasing nuclear energy outward. This nuclear energy balanced the inner gravitation force and our Sun became stable.

There is a big gap between Mars and Jupiter and this gap is filled with numerous smaller particles which is called the asteroid belt. Why was the planet not formed in this gap? This is because Jupiter is a huge mass close to the Sun’s mass. So if any planet tried to form itself was burst into pieces by Jupiter! Thus we have this beautiful solar system with the Sun at its centre and planets around it!


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ATOMIC STRUCTURE

1. History of Atom

In 460 B.C., a Greek philosopher, Democratism, developed a kind of idea of atoms. He looked at things around him and felt that if you go on breaking any material into parts and further parts, you will have to reach something which can’t be broken further. This he called an atom. It was purely speculation and no experimental evidence was available at that time to prove anything.

More than 2000 years had to pass before people began to consider the idea of atoms seriously. In the 1800’s, an English chemist, John Dalton did lot of experiments with several chemicals and he found a strange thing. Elements always combined with each other in fixed proportions. Any extra amount added would come out as residue. An element A for example would combine with 2 B’s by weight. This will always remain true. How can this be possible unless some fundamental particle in one element is combining with some fundamental particles in another, the number being always the same? Thus he proposed that every element was made up of fundamental particles and he called them by the same name atoms.

Thomsons ‘Rasin in the Pudding’ model of the atom

In 1897, the next great event took place. A negatively charged particle was discovered by J.J.Thomson in his experiments with discharge of gases. He called the negative charge particle electron. He also proposed a model for the atom. Since matter is not negatively charge he felt that there was a positive charge that balanced the negative charge and the electrons were put like raisins on a lump of pudding that was the positive charge.

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Berlin proved that when the energy is released when heated until it glows, this energy always comes out as discrete units, that is it takes only multiples of certain basic values. The energy was not continuous. He called these energy packets quanta.

At that time light was considered to be a wave but Albert Einstein thought otherwise. He felt that light was made up of quanta and he called this quantum of light Photon. Einstein also discovered the photo electric effect, the phenomenon by which a material gives out electrons when light is put on it and absorb. By this time people wondered about light. What was it really? A wave or a particle? Finally they came to the conclusion that light sometimes behaves as a wave and at other times behaves as a particle (but never both). The behavior which actually comes out depends upon the set up of the experiment. During the same time, alpha particles were discovered which had a positive charge. Scientists felt that this was the positive charge in the atom. In 1911, a land mark experiment was performed by Earnest Rutherford. He felt that it would be interesting to bombard atoms with alpha rays. He just wanted to see what would happen. He used radium to generate the alpha particles and shown them on to atoms in a thin gold foil. Behind the foil sat a fluorescent screen for which he could observe the alpha particles impact.

A strange thing happened. Most of the alpha particles passed through but occasionally some were hit back as if striking something hard! The only explanation of this was that most of the atoms had empty space in between and with hard points here and there.

Rutherford proposed his planetary model of the atom. He said that the positive charge was concentrated at the centre called the nucleus and the electrons moved round it like planets. But there was one terrible problem with this model. By the time a lot had been discovered about electricity and magnetism in general. A negative charge moving around the nucleus should lose energy by generating electro magnetic waves. Bohr used the principle energy comes in dissect packets of energy called Quanta to come with his model of the atom. He proposed that only some special orbits are allowed for electrons to move around. These orbits are called energy level. When electron gains energy it jumps from lower to higher orbit. When it looses energy, it jumps from higher to lower. Electron can’t have an intermediary between two levels. The energy difference between two levels is the quanta.

In 1932, J. Chadwick another sub atomic partial called the neutron. The neutron has mass nearly equal to the proton and has no charge. The mass of the nucleus is equal to the sum of the masses of the protons and the neutrons.


2. How are the electrons distributed in the difference orbits


To keep an atom electrically stable, it has the same number of negatively charged electrons in orbit around the nucleus as there are positively charged protons in the nucleus. In situations where there are either more or less electrons in orbit than there are protons in the nucleus, the atom is called an ion. This happens in static electricity and in some chemical solutions.

Electron shells

Electrons are arranged in shells or orbits around the nucleus.

Maximum number

There is a definite arrangement of the electrons in these shells and a maximum number of electrons possible in each shell.

Shell or Orbit Number 1 2 3 4 5

2 8 18 32 50

The most electrons possible in the first shell are 2. After the first shell is filled, the second shell starts filling up, according to the number of positive charges in the nucleus. The most allowed in the second shell is 8 electrons. Then the third shell starts to fill.

Electron shells for a Sodium atom (atomic number 11, with 11 electrons)

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Filling order complicated

After the second orbit or shell is filled, things start to get complicated. The third shell fills until it gets to 8, and then the fourth shell starts adding electrons until it too has 8 electrons. Then the third shell fills until it gets to 18.

Outer shell basis of Chemistry or valency

The number of electrons in each shell is the basis of chemical combinations.

Energy levels

Electrons have potential energy, depending on their shell or orbit. Each orbit has it’s own energy level. The each energy levels are further broken into sub orbits. There are some situations when an electron will jump from one orbit—or energy level—to another. When that happens, the electron gives off electromagnetic energy of one wave length or colour of light.

Since each element has its own electron shell or energy level configuration, it has own set of colours called its spectrum. This is used to identify any element.

The power of the Atomic theory :

What a reality, the atomic structure is! It is a deep fact about the whole physical world and explains so much! As we already saw in the earlier chapters, it explains sound (propagation of waves due to spring like disturbances of medium.) It explains heat. Heat is nothing but the jiggling and wiggling of atoms. It explains the giving off of light of a certain colour. This happens when electrons jump from one orbit to another.

Electric current is nothing but free electrons moving in metals due to a potential difference. Magnetism in magnets is the result of the molecular atoms in matter that are aligned. All the macroscopic properties can be explained by the atomic theory. Examples are state (solid, liquid or gas), pressure of gases, strength of materials (more bounding of the atoms inside, more the strength), temperature (average energy of movement of atoms in a body), density (more packed the atoms, more the density) etc. The whole of chemistry that is chemical combination depends upon valency as mentioned earlier. Hence chemistry fundamentally is based on atomic theory. The foundation of biology is chemistry and hence even biology depends upon atomic theory (the formation of complex molecules).

ELECTROMAGNETISN

1. Charges and force between charges

Electricity is related to charges. What is charge? Charge is a strange thing given in nature. It is not seen or felt ordinarily. For example if you touch a table you feel no effect due to charge.

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Around 200 years back, charges were discovered to be in matter by the simplest process of rubbing two substances. Much later they came to understand the fundamental essence of charges. This happened when they discovered that all matter is made up of atoms and molecules (molecules are only atoms joined together).

In an inch of any material, there are crores and crores of atoms / molecules ! ( see the next chapter for the details) Now electricity is a property of electrons and protons. Electrons and protons are in atoms. Electrons are negatively charged, protons are positively charged and there is a third type of particle called neutrons. Neutrons have no charge. The negative and positive are only names to say that there are two kinds of charges. The protons and neutrons reside in a central nucleus. The electrons orbit around the nucleus. Now, the property of these two kind of charges (positive and negative) is that positive and positive repel (go away from each other), negative and negative repel and negative and positive attract! This is given in nature !

When two substances are rubbed with each other, electrons from one substance (Say A) escape into another (Say B). B has now more electrons than protons so it has negative charge. B has lost electrons, so it has more protons than electrons.

So it has positive charge. Thus A and B attract each other since there are unlike charges. If A is taken to similar negatively charge body C, A and C repel. If B is taken close to a similar positively charged body D then B and D also repel. Repulsion happens because like charges repel. The force between charges (the repulsion or attraction) is called electrical force. The closer the charges are, greater the force. More the charges, more the force. This is expressed in the equation f = k q1 q2 / r2 , where q1 and q2 are the charges of the two bodies and r is the distance between them. This is called Coulomb’s Law.

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2. Currents, Ohm’s Law and Batteries


Currents are flow of charges in a conducting wire. How can such a flow of charges be created. Currents can be created using batteries. It was Volta created the first battery.

Working of a battery :

A battery has three main parts: a positive electrode (terminal), a negative electrode, and a liquid or solid separating them called the electrolyte. The positive and negative electrodes are separated by the chemical electrolyte. It can be a liquid, but in an ordinary battery it is more likely to be a dry powder. When you connect the battery to a lamp and switch on, chemical reactions start happening. One of the reactions generates positive ions and electrons at the negative electrode. The positive ions flow through the electrolyte to the positive electrode. Meanwhile, the electrons flow around the outside circuit to the positive electrode and make the lamp light up on the way.

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parts of a battery

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Principle of a battery

understand the mathematics of current. The current in a wire is directly proportional to what is called a potential difference between two points. Potential difference is defined as the work done to carry a unit positive charge from one place to another.

The more the potential difference, more the amount of current. V a directly proportional to i. So V = i x R Where R is the resistance in the wire to the flow of current. Current is measured in amperes and potential is measured in volts. Resistance is measured in Ohms. This relationship between potential and current is called Ohm’s Law.

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3. Magnetic effect of current


We have learnt about charged particles. There are positive and negative charges. We know that like charges repel and unlike charges attract. We have also seen that a current can be created through a battery and we have also understood Ohm’s Law.

It was first observed by Oersted that a magnetic needle is affected near a current carrying wire. He accidentally discovered this phenomenon while giving a lecture. It was one of the greatest turning points in the history of science !

Current in a wire brings about a magnetic effect in the space around it. To put it simply current in a wire behaves like a magnet. What is the direction of the magnetic field created by current carrying wire. This is given by the right hand thumb rule. If you imagine holding the current carrying wire in your right hand and with your thumb pointing in the direct of the current, then the curl of your fingers gives the direction of the magnetic field. See figure.

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4. Electro magnetic induction


We have seen that a current carrying wire produces a magnetic effect. Is the reverse true ? Is there a relationship between magnets and currents ? Michael Faraday wondered about it and tried many experiments and finally discovered that if you move a magnet near a wire, current is induced in it. This is called electro magnetic induction and this was used to make a generator.

So in effect we have two principles. The current carrying wire brings about a magnetic effect and moving magnet induces current ! These are the fundamental laws of electricity and magnetism !

Electromagnetic induction

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5. The working of motors


Motor work on the principle that a current in a wire creates a magnetic field. What we do is we take a coil bent it into a loop and place this coil between two magnets. The right hand side and left hand side will experience opposite forces of repulsion. Thus they will be turning motion. A turning motion is a called a torque. In practical motors many loops are taken and magnets are replaced by electromagnets.

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6. The working of generators


Generators work on exactly the opposite principle. Here the loop is given a motion so that electric current is induced in it.

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7. Electromagnetic waves (Spectrum)


We have two principles till now. Firstly we saw that when a current flows in a wire it becomes like a magnet creating a magnetic field around it. When such a wire in the form of a loop is kept between two magnets, we have a motor.

Secondly we saw that if there is relative motion between a magnet and a wire a current is induced in the wire. This principle is used to make generators.

Now, the current in a wire is steady. What if the current oscillates ? In other words, what if the current is not steady. A wondrous thing happens ! The changing current creates a changing magnetic field. But according to Faraday’s Law this changing magnetic field should create in turn electric field. But the changing electric field again creates a changing magnetic field and so on.

So when a current is not steady, electric and magnetic fields are created and they propagate outwards as waves. And these waves are called electro - magnetic waves. Maxwell found out the velocity of such waves and it was exactly equal to the velocity of light. Thus they discovered that light waves actually are electro magnetic waves. Electro magnetic waves have various frequencies and wave lengths and the whole range is called the electro magnetic spectrum.

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LIGHT

1. WHAT IS LIGHT AND WHAT ARE ITS PROPERTIES?


Light is one of the most mysterious things on the world. We don’t see light, we in fact, see because of it. Anything heated becomes luminous, is itself glowing, and enables us suddenly to see things around it. If you are sitting in a dark room, by an can’t see anything. When you switch on the light, the bulb glows and other objects are seen! How, what is happening? Clearly the bulb is the source of light and if we close our eyes, we can’t see, obviously. Something mysteriously is happening between the source of light (here bulb) and our eyes.

What is it?

Something is travelling between the source and our eyes. And this something seems to travel on straight lines. Otherwise why would there be shadows if anything obstructs that something coming from the source of light. (here bulb) Then, there are colours. It is as if light comes in a variety of colours. A red short is red, may be, because that mysterious something is a type that causes the sensation of red.

Red is red. We can’t question it. It is that particular quality. What we are doing here is trying to ask what causes red. That which causes on us the sensation of red is “red light”. In the same way violet light, yellow light, blue light, green light, indigo light, orange light.

What about black colour and white colour. White is a mixture of all colours and black is that which gives off no colour. When light, that invisible thing, falls on a particular object, the object absorbs some colours and gives off a colour. The colour given off, if red, will make us see red. Similarly with other colours. If the object gives off all colours, we see white. If the object absorbs all colour and gives off no colour, we see black.

If the object lets the light pars through completely the object is not seen eg: glass, water. What if the object does not take anything and reflects the light from an object completely. Then it becomes a mirror!

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See the figure. The light from object A travels on straight line and hits the mirror. The mirror doesn’t take anything and simply reflects it and then it reaches our eye. Now comes the catch!

What do we see! Since all the light from A has reached us, we see A but where do we see A?

From childhood our brain knows only to ‘see’ objects in straight lines. So it sees the object at A as shown on the figure!

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See figure(2) the object itself has the eye. Then we see ourselves at a obstance which the same distance ‘d’ but ‘inside’ the mirror! In a way the objects that we see is a hallucinatism but it is a hallucination due to physics and it’s reality not due to a ghost! Let us now consider another and last strange phenomenon that we see with our naked eye.

Why does the win in a glass of water appear to be above than it’s normal bottom? Why does a stick seem to bend in water? The answer is that light bends when travelling from one medium to another. (Here from water to air). So what? What if it bends?

If we take two rays - ray 1 and ray 2 and if it bends and reaches our eyes, our eyes don’t know that. It sees on straight lines only and that means that it hallucrates and sees the object above than the normal. Even the bottom comes up.

A spom bends and bulges from the same reason.

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So these facts give us some ideas about light which are fairly obvious. But it is a wonder, isn’t it?

Its strange - this thing that travels in straight lines, bends when travelling from one medium to another, is composed of various components which cause various sensations of colours in us!

Light travels in straight lines

Light consists of various colours

Light is reflected from norms

Light is refracted (as it is called, the act of bending) when from one met to another.

When Light strikes one face of a prism, the different colours of light refract by different amounts! Thus they emerge from the other face with the colours separated. Rainbows are formed that way (the raindrop acts as prism)

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The principle of refraction is used in lenses to make things bigger.

HEAT

1. WHAT IS HEAT REALLY AND WHAT ARE ITS PROPERTIES ?


Heat is a sensation that we feel, but what is that sensation and how is it caused? Heat in the earlier times was thought to be a kind of fluid that goes from one body to another. But later they understood that heat is nothing but the jiggling and wiggling of atoms and molecules. Matter is not all one piece. Inside it is made up of crores and crores of atoms. These atoms move randomly and more the movement of the atoms, more the heat. Our skins have evolved to precise heat with a sensation of hot and cold! In a cold night, why do we feel cold? It is because the molecules of air move about at less average energy( called kinetic energy). When we rub our hands - hard lot of heat is automatically produced. Why? Again it is because when you rub your hands together, the atoms inside jiggle more and more and that gives us a sensation of heat! So when pressure is increased then heat is produced. The pressure can be due to friction, electricity. Then there is another thing that heat does , it can change the state from solid to (picture)


Change of State


liquid and liquid to gas! Why does this happen? It happens because in a solid the atoms are fixed in their places. They cannot move about and when heat is given to such a solid, the bonds etween the atoms that keep them fixed weaken and they move about though the link between them does not break. This is a liquid. On further heating, the links that is the bonds are broken completely and that is a gas obviously!

Heat also expands solids, liquids and gases. This is because the bonds between the atoms inside get loosened and the body as a whole expands. (Picture)


Expansion of Solid


Heat is also transmitted in 3 ways - conduction, convection, radiation. When one part of a solid body is heated, the atoms inside that part starts jiggling and wiggling. These in turn moves the atoms beside them and so on. Thus heat is transmitted from one end to the other. This is conduction(see Picture)

Convection is very interesting. Suppose we take a bucket full of water and heat it for sometime. The lower part which is closer to the heat gets heated up. The bonds inside loosen up and the distance between the atoms become greater. When the distance becomes greater it is like the weight is reduced as less is now in the space occupied earlier. The gravitational attraction hence reduces and the water goes up. The colder heavier water pushes into its place (the lower part of the water). Thus heat gets transmitted by actual movement of water. This is called convection. Exactly to the same thing happens causing winds. The air closer to the earth is heated up, becomes lighter due to the atoms going further apart and hence rising due to less gravitational attraction. The colder heavier gas pushes into its place and winds are caused!

There is a third way in which heat is transmitted. They are through waves. There are waves called heat waves or infrared waves. They are part of the electromagnetic spectrum (to be covered in a later section). These waves do not need any medium. The sun’s heat is actually heat waves which travel through space and come to earth !

GASES

1. BERNOULLI’S PRINCIPLE

Statement:

The pressure of a liquid is decreased if the velocity with which it is moving is increased. Why is this so? This is because a flowing liquid (or even a gas) is made up of molecules. When these molecules hit the surface it is a pressure. When the molecules are going fast, the number of hits are less and hence the pressure is less.

This principle is used to make airplanes fly. What we do is we make the wings of the airplane in such a way that air needs to travel a longer distance on the top surface when compared to the bottom surface. Since the air is moving smoothly on both the surfaces, it takes a longer time for the air moving on the top surface to cover the wing as compare to the air that is moving along the bottom surface.

This means that the velocity of the air moving on the top surface is less when compare to the velocity of air moving along the bottom surface. Hence the pressure on the top surface is lesser when compared to the pressure on the bottom surface. So there is a net upward pressure on the bottom surface and airplane flies! (see figure)

2. WHAT ARE THE PROPERTIES AND LAWS OF GASES?

2.1 What is a Gas ?

A gas is a substance that can compressed easily. Gases fill the container in which they are put. Actually the atoms and molecules in a gas are free to move about. There are spaces in between molecules ! That’s why it is a gas ! There are three fundamental variables that define the state of a gas. They are pressure, temperature and volume. These three variables are connected deeply in the form of laws. The first law is Boyles law. This gives the connection between pressure and volume. Pressure is the force per unit area on the wall of container. Volume is the space occupied by the gas. How are these two related and why ?

2.2 Gas Laws

Boyle’s law

If you increase the volume keeping temperature constant, there will be less molecules per unit volume. Hence the hitting of the molecules of the container will be less. Hence the volume is inversely proportional to pressure. This is called Boyle’s law. The next law is Charle’s law. Charle’s law states that the volume of a gas is directly proportional to its temperature provided the pressure is held constant. It is because if you increase the temperature and pressure is kept constant, then the body will increase in volume due to increased movement of molecules.

These are the two fundamental laws that govern all gases.

LIQUIDS

1. Introduction:

When we look around the world we see actually 3 different kinds of things – Solids, Liquids and Gases.

What is the difference between solids, liquids and gases?

Solids have a definite shape, are reasonably rigid i.e. don’t change shape too easily.

Liquids do not have a definite shape and takes the shape of the container.

Gases are even more free. They fill the container fully.

Why do solids, liquids and gases have their nature.

If we keep ice in open air, it melts and becomes a liquid! After some more time, it becomes vapour and vanishes! Surely a solid is not all one piece. If it is becoming a liquid, there is an internal nature it has that gets changed. The same thing with liquid becoming gas.

Yes!

There is an internal nature to everything.

During the 19th century an extraordinary fact came to light.

Everything, an inch of any material, is made up of crores and crores of small particles called atoms or combinations of atoms called molecules.

The first indication came from experiments in chemistry and later many many experiments gave a detailed account of the inner working of atoms.

The story of the atomic structure is explained fully in the section of “understanding atomic structure”. In a solid the atoms are bonded tightly and hence outwardly, it is solid!

In a liquid the atoms are not in one place but are bonded!

In a gas the atoms are free!

This is the reason why a solid is a solid, a liquid is a liquid and a gas, a gas! When heated, the bonds between the atoms in a solid become weak and becomes a liquid outwardly. On further heating, the bonds become completely broken and a gas is formed. We discuss change of state in the section of “understanding heat”.

In this section we try to gain a deeper understanding into liquids. Liquids and solids together are called fluids.

Pascal’s law, Archimedie’s Principle, and Bernoullis principle explain the deeper working of liquids. Bernoulli’s principle applies to gases also and will be considered in the next section on, Fluids (2) – gases.


2. Pascal’s Law


Pascal’s Law states that if you apply a pressure at one point in a liquid, it spreads equally in all directions.

What does this mean?

A liquid is a liquid. This means that it does not resist. If you apply a pressure at one point, obviously it will get transmitted to all points in the container and in all directions. It is because a liquid does not resist a force that this happens.

Pressure is force per unit area.

Why do we need a concept like pressure for liquids (gases too) and not just force? Liquids do not have a definite shape. It takes the shape of the container. So we cannot use the concept of force. The effect of the force depends on the largeness of the surface on which force acts.

If the area of the surface is large the effect of force would be less. If the area is small, the effect of force would be more.

Thus both force and area are important and this is pressure, the force per unit area does give the pressure.

If the force is 8 Newton and the area in which the force is acting is 4m2, then the effect of force i.e.


Pressure = 8/4 = 2N/m2

If the force is halved (4 Newton) and the area is halved (2m2)


Pressure = 4/2 = 2N/m2


Both factors force and area of contact comes in to play to determine pressure.

Now, Pascal’s law can be used in a dramatic way in a hydraulic press.

Consider the figure below…

If a force is applied at A, a small force, for a long distance l, it gets transmitted to B, a great force for a shorter distance D,


So f x d = F x D (Pressure is the same on both the surfaces)


Thus a small force for a greater distance causes us to lift heavy objects by giving a greater force with a smaller distance.






3. Archimedes Principle





Archimedes was a Greek and he is famous for having discovered a principle that governs all liquids – the Archimedes principle. Let us proceed how to understand his principle.

It is a common observation that when you push a body into a bucket of water, you experience a force in the opposite upward direction. This means that the water exerts a force on you when you immerse a body in water.

If you just put the body in water, it either floats or sinks.

Now why does a body thrust into water or every liquid experience an upward, resistant force?

Why do some bodies float and some bodies sink?

These questions are answered by the Archimedes Principle. When you put a body in water, that body displaces water. The l….. of the water rises. How much water is displaced?

Obviously the volume that the body has occupied in the water, that much of volume of water is displaced. See the figure 2 below.

Now, the displaced amount of water tries to get back into its on final position and thus gives an upward force to the body. This is called the Buoyant force as it is trying to keep the body up.

Obviously this buoyant force is equal to the weight of water displaced.

This is the Archimedes principle.

Now, when does a body sink?

When the weight of the body is greater than the upward force which is nothing but the weight of water displaced, the body obviously sinks.

When the weight of the body is less than the upward force, the body obviously floats.

So clearly 2 things are important here.
The weight of the body itself.
The amount of water (or liquid) the body displaces.

If ‘2’ > ‘1’, the body floats. When ‘2’ < ‘1’ the body sinks. A work floats on water because its weight is less than the amount of water displaced (which gives an upward thrust).

An iron nail sinks on water because its weight is more than the water it displaces i.e., the upward thrust given to the nails greater than the weight of the nail. But what about an iron ship? Why does an iron ship float and not sink in water?




The ship is heavy but it is big in terms of volume also. When it enters water, the amount and hence weight of water it displaces is also huge and the upward thrust is huge!

The upward thrust in the ship is actually more than the weight of the ship! Thus the ship floats!

Thus we see both the factors acting always when we consider floating / sinking
Weight of displaced water that determines the upward thrust on the body.
Weight of the body itself.

‘1’ > ‘2’ – body floats.

‘1’ < ‘2’ – body sinks.

All bodies whether they are floating or into water experiences thrust upward thrust. This is equvalent to weight loss.

The weight acting downward is contracted by a buoyant force upwards.

Apparent weight loss = weight of body – upward thrust (buoyant force)

Thus we clearly see how (and why) bodies behave the way then do when immersed in liquids.