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My Pages On Different Subjects which Hyperlinked to all my Blog Posts

Sunday, 1 April 2012

Electricity, Magnetism,Electromagnetism : Major Forces which Carry Forward Modern Technology to its Highest Level Throughout the modern world


Some 600 years before the birth of chirst, a greek philosopher called Thales discovered that amber  (in Greek elektron) , a fossil resin ,could attract small peices of fluff or feather, after being rubbed with fur .His discovery laid thr basis for the whole science of electricity .The british scientist Willium Gilbert (1544 1603)  , first suggested that the word electricity (from the greek elektron) should be used to describe this force.

Idol Of Thales

If you comb your hair with a plastic comb you will find that the comb can attract small peices of paper.This is the effect Thales saw in his experiment,What creates this force of attraction ? Until the end of 19th century no one knew the answer .Now we know part of the answer ,but not all.


The central nucleus of atom consist of protons and neutrons. Protons have a positive electric charge and neutrons have no electric charge and move round central nucleus .Each atom contains the same number of electrons  as protons.The charge on the electron is exactly equal but opposite to the charge on the proton.So an atom has no charge and we say it is electrically neutral.

Same Charges Repel Each other

When you pull a comb through your hair ,some of the electrons from the atoms of your comb are left behind on your hair. So the protons in this atoms donot have the sufficient electrons to balance them .The result is that the comb is positively charged.The comb is then able to attract the electrons in the atoms of the paper .This creates the force between comb and paper.

Opposite Charges Attract each other

The kind of electricity produced by the comb is called static electricity. The basic rule of static electricity .The basic rule for static electricity is that unlike (different )charges attract ,and like (the same )charges repel one another .A positive charge and a negative charges will always repel ane another.We can measure the attraction and repulsion of electric charges .We know the about electricity in atoms.But we still donot know exactly what ann electric charge is or what the difference is between negative and positive charge.



Unlike charges attract each other , like charges repel each other .The size of the force , in both cases depends on the size of the force, in both cases ,depend on the size of charges .It also depends on the square of the distance between the charges .This mean that if the distance is halved, the force is four time bigger.

Respective forces  of two point charges are directly propertional to their multiplication of charges and inversely popertional to the square of their distance. The force is activated on two point`s connecting straight line.
Suppose Charges of two respective points are q1 and q2 and distance between two points are r, then according to Coulomb`s law force F is:-

       q1 q2
F a -----
        q1 q2
F = ------------
         k r

( k = Dielectric constant or Specific inductive capacity S.I.C)


Internal Structure of Van De Graff Generator

It is used to produce a higher electric charge in science laboratories.The air molecules are broken up at the lower points.A positive charge is carried up on the moving belt .This charge is then conveyed to the insulated metal sphere by the upper set of points.

Unlike charges attract each other, like charges repel each other . The size of the force , in both cases, depends on the size of the charges. It also depends on the square of the distance between the charges.This means that if the distance is halved, the force is four times bigger.


Lightning In the sky occur due to the Friction of Charges in atmosphere

Is you comb your hair in a dark room and then hold the comb close to your thumb you will see a small spark .This is because the energy  stored in the charge is making the air atoms between the comb and your thumb emit light .In 1708, a British scientist called Willium Wall suggested that a lighting flash in the sky was a similar process on a grand scale.


Experiment of Benjamin Franklin

50 years later an American inventor,Benjamin Franklin,carried out an experiment to try to prove that a lightning discharge was in fact ,caused by electricity.In a thunderstorm he flew a kite to which he attached a metal wire . The wire was connected to a silk thread,The other end of of which was held by Franklin.A metal key was attached to the thread just above Franklin`s head .Franklin flew the kite into a thundercloud and then held a Finger close to the key. The spark jumped across the gap.Each time Franklin flew the kite into the thundercloud he made the key spark.This proved that thunderclouds were charged  with electricity and that some of the charge was being conducted down the silken thread to the key . The build up of charge on the key caused a spark to jump the gap to his finger.

It was a brilliant experiment but a very foolhardy one .The next person to try it was killed by the discharge.Franklin very lucky escape with his life.However the risk he took turned out to have well worth it. Having shown that lightning is caused by an electric discharge ,Franklin went on to invent a way of protecting tall buildings from being struck by lightning.The invention was a simple step from the kite experiment. He attached a metal rod to thye hightest point of a building and connected the rod bya a wire to the earth .Thus is lightning struck the building the charge was led safely down the wire to the earth.

Damage by lightning has been greatly reduced by the use of lightning conductors,Even so, throughtout the world ,on average some twenty people a day are killed by lightning.

Lightning Rod on top of the big building help to Passes harm full electric charges into the ground from the sky

Lightning can pass from one cloud to the ground .In both types a single flash usually consists of between five and ten closely spaced strokes following the same channel. The inteval between the strokes following the same channel .The interval between the strokes is only a few hundredths of a second and to a human eye they appear as one flash.The current carried by each discharge heats the air causing it to expand .The repeated expansions and contractions caused
by the five to ten strokes generate massive sound waves.This is the thunder .As light travels more quickly than sound there is a delay between seeing the flash and hearing the thunder .The speed of sound is 330 m per second .So for every second`s delay between seeing the flash and hearing the sound the thunder has travelled 330 metres.

In storm clouds the cold upper part of the cloud contains positively charged particles.The middle region contains negative particles. The rain areas at the base of the cloud are sometimes positively charged .When lightning flashes from
the negative part of one cloud to the positive part of another cloud it is called cloud-to-cloud lightning.When it flashes to earth it is called cloud-to-earth lightning.

The metal lightning conductor at the top of the Church tower conducts the electricity of the discharged down the metal conductor safely to earth.The lightning conductor was invented by Benjamin Franklin.

Electrical transmission lines are sometimes struck by lightning, as they have sharp points sticking up from the ground.When the lightning strikes the pylon,large voltages build up across the insulators.This can cause them to breakdown.The line may then have to be repaired.

If you connect the torch bulb to a battery through a switch you have a simple electric circuit. When The switch is open there is no flow of electricity. When you complete the circuit by closing the switch electricity flows through the wires from the battery and the bulb lights. What is it that flows through the wire when the switch is closed an electric current consists of a flow of electrons and it is this flow of electrons that the switch inrerrupts.


An electron is a very  tiny negativly charged particle to make the torch bulb stay alight for one second takes a flow of about one million million million electrons .These electrons occur in atoms . Atom consist of a central nucleus. The electrons move round the nucleus, at different distances from it in groups called shells .The simplest atom is Hydrogen,
consisting of  one electron circling round the nucleus. The atoms of different elements all have different number of electrons.

Showing First 18 elements in periodic Table  and their shell of the electrons

Each shell of an atom can contain a certain number of electron. In the atom of most elements the outer shell is not full .Atoms combine with each other to form molecules they tend to do this so that the combining atoms each end up with full outer shell. Atoms with only a few electrons in their outer shell may do this by losing their outer electrons. These outer electrons detach themselves from the nucleus and wonder at random around the atoms.Elements which can combine in this way are called metals .They conduct electricity because these detached electrons are free to move.

Atomic structure of Element Sodium

The function of the battery in the simple circuit describe to push the free electrons in the metal wire so that they all move in the same direction. When a current flows through a wire,It consists of these detached outer electrons all flowing in the same direction .When the switch is turned off and the battery is disconnected the electrons cease to have this push and they return to random motion.

Electrons during current flow

When the torch switch is pushed down, the electrons flow through the wire nad pass through the very thin wire in the bulb.This wire is called filament.The wire is so thin that the collisions between electrons and atoms are much more frequent.This increases the temperature of the filament and makes the atoms emit light.The filement emits red light and then, when it gets hotter, white light.

Electrons not only flow through wires ,they also flow through nerves in the body. For example,when you see something, an electrical impulse travels from your eye to your brain.These impulses consist of a flow of eletrons passing down the optic centre of the brain.Muscles,too, are controlled by a flow of electric pulses from the brain passing down nerves to the muscles.


Simple Circuit with Battery,Switch and Bulb with holder

A simple circuit consisting of a torch bulb, a battery, three pieces of wire and switch.When thespringly metal strip of the switch is pressed down the electrons flow round the circuit and the light bulb lights up.

The atomic nucleus consists of tiny particles called protons and neutrons. The proton is positively charged and the neutron has no charge.There are negatively charged electrons around the nucleus.Each atom has as many protons as electrons. So their charges balance each other out. In the hydrogen atom the nucleus consists of one proton. Neutrons
occur in all nuclei except hydrogen.

In a metal wire the outer electrons move at random about the atoms.When a current flows these electrons all move in the same direction.

The first 18 elements, in the centre of each is a positively charged nucleus. The charge on the nucleus is equal to the number of electrons circulating around it. The chemical properties of each element depend on the number of electrons in the outer shells of its atoms. If the electrons become detached, as they do in metals, the substance can conduct electricity.

Bulbs are joined in series way

These two bulbs are connected in series.The voltage is shared between the two bulbs.

Bulbs are joined in parallel way

These two bulbs are connected in parallel.They both receive the full voltage from the battery .This means that they are both at full power so the battery will only last half as long as when they are connected in series.


About 500 BC tha ancient Greeks discovered that a certain type of black stone had the powre of attracting peices of iron .This mineral was an ore of iron and is called magnetite. Anything that has this property of attracting iron is called a magnet and the property itself is magnetism.

Magnetite is a compound of iron and oxygen .The common magnets that you see are made of iron or steel. A magnet can have any shape but is usually in the form of a bar magnet or a horseshoe magnet .

The Greeks used to think that pieces of iron stick to a a magnet because it has small hooks on its surface. It is easy to show that this cannot be true .If you push a magnet close toa pin the pin will jump to the magnet . You can also attarct
object by magnetism through a piece of paper.


Two things do not have to be touching one another to be attracted by magnetism .How do they affect one another? How does the pin  know that the magnet is close to it ? Obviously there must be some influenceof the magnet passing through space . One way in which scientists have tried to explain this influence is by thinking of magnetic fields. The magnet affects the region around it and can influence other magnets or magnetic materials in this region.This region is called a field of force or a magnetic field.

Lines of Forces of Horseshoe Magnet

It is possible to show a magnetic field by laying a piece of paper over a magnet and sprinkling iron filling on to it .When you tap the paper the fillings arrange themselves into a pattern .The iron fillings cluster together in the regions in which the magnet has most effect , that is , in the places where the field is strongest .You can see that there are more fillings close to the ends or poles of the magnet .They also tend to arrange themselves in lines running between the poles of the magnet .These are called lines of force and are imaginary line running from one pole of the magnet to the other.They show the direction in which the magnet acts when anything is put into its field.The influence of a magnet falls off as one gets further away from it. We say that its field gets weaker.


The earliest use of magnets was in compasses,for showing direction. This use depends on the fact that the earth has a
magnetic field .It acts like a large bar magnet Think of the earth spinning on an imaginary axis .One end is north pole and the other the south pole .These are called the geographical poles of the earth .The earth is acts like a large bar magnet laying almost along the axis .Any magnet suspended in the field will line up with the lines of force .The needle of a compass is a small magnet and always points north and south .The end of the magnet pointing north is called its north seeking   pole,or north pole .The other is its south pole.

In fact the compass needle does not point to the true north pole.Its points to the magnetic north pole which is many hundred kilometresfrom the true north pole.Navigators always have to make a correction for this variation of the compass .This is complicated by the fact that the position of the magnetic polesvary slightly from year to year .In some places the needle of the compass does not read true because of amgnetic material such as iron ore in the earth , or a large peice of steel nearby .A compass can be shielded from stray magnetic fields by a peice of soft iron.


1) Like poles repel , opposite poles attract.

Opposite Poles of magnet Attract Each Other

Same poles Repel Each other

2) A chain of pins hung from the a pole of a Horseshoe-magnet .Each pin is made into a magnet as shown here. Notice that the north pole of the Horseshoe-magnet induces a south pole on the end of the pin.

Horse-Shoe Magnet

3)Field of the both Horseshoe-magnet and bar-magnet show by the lines.There are lines of force running between the poles of the magnet.

Line of Forces of bar Magnet


Frence scientist Coulomb discovered the law of respective forces of two magnetic poles. The law is :
The attraction or repulsion forces between two respective magnetic poles are directly propertional to multiplication of
their polepowers . Also inversly propertional to magnetic poles distance square. If m1 and m2 are the polepower of two magentic poles and its distance is r , if poles respective force is F then according to the Coulomb`s law:

        m1 m2
F = --------------
          m r


Earth act as a large magnet and this is why a compass needle can be use to show north and south . The needle is small
magnet balanced on a pivot and it always come to rest along the line of force. In fact the earth`s magnetic field is not symmetrical , as shown. It is distoreted by the influence of the sun`s magnetism.

Earth`s Magnetic Field


In magnetic materials like iron, the atoms themselves are little magnets. Usually they all pointing to different directions so the metal is not a magnet. In a magnet the atom magnets all point in the same direction .If it is brought close to the unmagnetized it causes the atom magnet to line up and thus makes the iron metal into magnet. When the magnets are heated , they loose their magnetic properties because the heat disarranges the atoms. A magnet can also be demagnetized by hammering it or dropping it.

Non Iron Bar change into Magnet after rubbing it with magnet Bar


The Aurora Borealis or nothern lights seen at night in artic regions and is caused by charged particles from the sun trapped by the earth`s magnetic field. In Antarctic the aurora australis is seen.


You can make a electric current magnet using a length of copper wire and a large nail many times and tape it in place. Join the end of the wire to the terminals of a battery through a simple switch , switch on. Bring the nail head near some paper clips and drawing pins and watch them jump to it . By winding the wire in a coil around the nail , you have made it into a magnet. We call such a magnet an electromagnet.

Ordinary Iron Nail Become Magnet and attract small pins after electricity pass through it

In 1820 a danish scientist,Hans Christian Orsted made a very important discovery. He noticed that a magent was affected
by an electric current flowing in a wire. You can easily do a experiment similar to this .Take a three volt battery , a length of a copper wire , and a small pocket compass . Connect one end of the wire to one terminal of the battery and lay the wire over the compass .Now touch the free end of the wire to the other terminal of the battery .The compass needle will change direction..When you remove the end of the wire it swing back to its original position. Do not keep the battery connected for too long or it will soon go flat.

The experiment shows that a flowing electric current produces a magnetic field.The shape of this field is not the same as that on an ordinary bar or horseshoe magnet but it has the same properties .In fact a current in a wire can be made to act
just like an ordinary magnet.

The "Switch-on-power" experiment shows how to make an electric current magnet .The coil of wire wound round a core
such as a nail is called a solenoid.Pass a current through it and put each end in turn near a compass needle. You will see that one end of the solenoid attract the north pole of the needle and other repels it. The solenoid has a north and the south pole just as a bar magnet has. Find out what happens when you change the direction of the current by connecting the battery the other way round.


Magnetism produce by an electric current is called electromagnetism .When you wind turns of wire around a large steel nail and connect it to a battery you produce a strong magnetic field .A magnet of this kind is called an electromagnet .

If you switch off the then current you will probably find that the nail still acts as a magnet .It has been magnetized by the effect of the current .Magnets of this kind are called permanent magnets.

If , instead of steel ,you had used a peice of soft iron as a core you would find that the magnetism disappeared when the current was switched off.It is not easy to do this experiment as soft iron is difficult to find.You may be able to make a piece by heating an iron nail to red heat and letting it cool slowly .The soft iron does not keep it magnetism like steel .It is a temporary magnet.

Electromagnets may have uses ,such as in electric bells, loudspeaker,electric motors and generators.

In fact that an electric current can create a magnetic field shows us where the magnetism of permanent magnets comes from .In a piece of magnetic material the atoms all act as little magnets .An electric current in a wire is a flow of electrons along it .So a magnetic field is formed by ,movement of electrons .We know that atoms contain moving electrons .Thus we can see that the magnetism of permanent magnet is caused by the motion of of electrons in its atom.


You can make a electric current magnet using a length of copper wire and a large nail many times and tape it in place. Join the end of the wire to the terminals of a battery through a simple switch , switch on. Bring the nail head near some paper clips and drawing pins and watch them jump to it . By winding the wire in a coil around the nail , you have made it into a magnet. We call such a magnet an electromagnet.


Galvanometer made with compass

This simple experiment shows how a wire produces a magnetic field.When the battery is connected the compass needle moves.

Compass Pointer Defect when current pass through the coil beside it.


Lines of Forces of a iron nail which is change into magnet

A coil of wire is called a Solenoid . It acts as magnet .You can make a good electromagnet by warpping coil around iron nail.Note that the more turns of wire you use, the stronger the magnet .The wire used has to be covered with an insulator.


A large elecromagnet can be used in  a crane for moving scrap iron . To release the load , the driver simply switches off the current to the coils of the electromagnet.


After Oersted had shown that an electric current could produce a magnetic field,scientist began to wonder whether they could use a magnetic field to produce an electric current .There were many attempts to do this. All were unsuccessful until in the 1830 s Michael Faraday began a series of experiments with magnets and coils.

To detect an electric current some kind of instrument has to used.The earliest form of current detector was the galvanometer.This was a compass surrounded by a flat vertical coil of many turns of wire. A current flowing through the coil produces a magnetic field which affects the compass needle.


One of the experiments performed by Faraday was to take a large wire coil (solenoid) and connect it to galvanometer.

Small amount of current is produce when bar magnet pass through the coil which shows in the galvanometer by Electromagnetic Induction

When the bar magnet was placed near the coil of wire the galvanometer was not affected  .No electric current was produced by magnet .How ever when when the magnet was pushed into the solenoid the galvanometer needle moved slightly and then went back to its original position .When the magnet was pulled out of the solenoid the needle "kicked"

in the oppesite direction .Faraday realized that an electric current was being produced when the magnet was moving .The direction of the electric current depended on the direction in which the magnet was moved .This behaviour is called electromagnetic induction. A moving magnet induces an electric current in the solenoid .This discovery was of immense

importance .Up till then electric currents had been produced by electric cells. Now a method existed for converting the energy of motion (mechanical energy) into electrical energy.

For example , if the magnet was continually pushed and pulled in and out of the solenoid , an electric current flowed first
one way and then the other .This produced an alternating current .A mechanical engine was used to move the magnet , making a similar generator. The current is induced in the solenoid when the magnet is moved because the magnetic field  is changing . A current also flows through a wire if the wire is moved through a magnetic field .Again ,The wire is cutting the lines of force.
Small amount of current is produce when bar magnet pass through the coil which shows in the galvanometer by Electromagnetic Induction

Faraday also did experiments on the opposite effect . When a wire is placed in a magnetic field and a current passed through it the wire moves .There is a force on it due to the effect of the current and the field . Thus we see that if a wire is moved through a magnetic field .A current flows in it. This principle is used in generating electricity.If a wire carrying a current is placed in a magnetic field . The wire is made to move .This principle is used in electric motor.

When the magnet moves into the coil the galvanometer needle moves one way . When it is pulled out of the coil the needle moves in the opposite direction .The current only flows when the magnet is moving.

In a simple Galvanometer a current passing through the flat coil produces a magnetic field.This deflects the compass needle and so the current is detected.


Small Transformer
Big Transformers

Transformers also worked by electromagnetic induction.They are used to change an alternating current of one voltage to an alternating current of another voltage .The current to be passed through the first coil .As the current increases and decreases it produces a magnetic field which also increases and decreases.This changing magnetic field induces a current in the second coil which has a different number of turns .The difference in the number of turns causes a diffrence in the voltage.

 large transformer used in a power station.The two coils of wire are wound on to the same iron core, one over the other.There are more turs of wire on the first coil than on the second.Because of this the voltage in the second coil is less than in the first.Tranformer like this are called step down transformers because they reduce the voltage.Step up transformers are also used.

There are two main ways of making electricity .The first is to generate it in a cell by chemical reactions.The second is to produce it by the electromagnetic effect using a rotating machine .Rotaring machines are called generators.Small generators are sometimes called dynamos.

When Large Electric- Coil is rotated between the Magnets it produce electricity which light up Bulb and Current flow according to Fleming`s Right Hand Rule  .

The principle of the generator was discovered by Michael Faraday. He showed that if a conducting wire is moved across a magnetic field an electric current is generated in the wire.

The most convenient way to arrange this conducting wire is to rotate a coil of it between the poles of a permanent magnet.This is exactly what Faraday did in 1831. The whole of aiur present way of life is based on his discovery.Without electricity modern society come to standstill.There would much less lighting and heating .There would be no movement from the millions of of electric motors that we use for trains. lifts,factory machines and the hundreds of other electrical appliances we use everyday.


Michael Faraday

Faraday`s first generator was a small laboratory-bench model that he rotated by hand. In the modern power station,machine rotate the genetarors. In a coil oil or nuclear power station the generator are rotated by steam turbines.The tubines are connected directly to the generators and the set is called a turbo -generator.

In a hydroelectric station the rotation of the generator is produced by a water turbine.These power station are situated
at a point of rivers where there is a fall of level,ususally at a natural waterfall.A dam is built to restric the waterfall and the water is led through a large pipe to the lower level where it rotates a water turbine.In all cases the turbo generator is a means of converting the energy into electrical energy.

Faraday disk, the first homopolar generator

If a coil of wire is rotated in magnetic field a current is produced in the coil .The direction of the current reverses as the coil rotates.The first half of the revolution produces a current in one direction , the second half in the other direction. This is shown by a graph having the shape of wave .The current varies Zero to maximum or minimum and back to zero in each half cycle because the strength of the current depends on the number of the magnetic lines of force the coils cuts.


Fleming`s Right Hand Rule

Fleming devised a rule ,Flaming`s right hand rule ,to work out in which direction the current flows in a conductor when it is moved through a magnetic field .If the conductor is in the shape of a coil , the current is oviously going to change direction as the coil the current produced by this type of machine is going to vary from nothing ,to a maximum
in one direction ,falling again to nothing when the coil is vertical. The current then reverses direction and builds up to a maximum in the opposite direction ,finally returning again to zero .This series of event is called an alternating current.
The number of times this cycle changes in one second is called the frequency.

In small machines such as a bicycle dynamo the magnetic field is produced by a permanent magnet .In the large machines the electromagnet is rotated  inside the coil of wire instead of the other way round.The effect is exactly the same the electricity is generated in the stationary coil (stator) by the changing magnetic field produced by the rotating magnet (rotor).

Fleming`s right hand rule is a way of remembering in which direction the current flows when a conductor moves through a magnetic field .The thumb , forefinger and second finger are extended at right angles to one another.If the thumb indicates the direction of the motion and the forefinger the direction of the magnetic field (North to south) then the second finger indicates the direction of the current.

In a bicycle dynamo the motion is obtained from the bicycle wheel of the dynamo rubs aganist the tyre and is thus made to rotate .The drive wheel is connected to a cylindrical permanent magnet that rotate inside the coil .Only one wire needed to rear light and front light because the dynamo is earthen to the frame which provide the other connection.In some bicycles the dynamo is built into the hub of the wheel.

The generator room of a modern power station .The huge steam pipes feed the steam turbine which drives the generator in the foreground

When Dynamo rub with the Bicycle Tyre it causes rotation to the magnet which is in between the coil produce electricity and light up the bicycle Light. 


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