Nicolaus Copernicus -- 19 February 1473 – 24 May 1543 -- was a Renaissance astronomer, and the first person to formulate a comprehensive heliocentric cosmology,
Joseph-Louis Lagrange -- 25 January 1736 – 10 April 1813 mathematician and astronomer, director of mathematics at the Prussian Academy of Sciences in Berlin,
Galileo Galilei 15 February 1564[4] – 8 January 1642),
Johannes Kepler -- December 27, 1571 – November 15, 1630 --mathematician, astronomer and astrologer,
Sunday, November 21, 2010
Friday, November 12, 2010
INDEX -- पुणे यूनि. सायन्स लेक्चर्स
2. Uniformly rotatint frame, centripetal Acceleration corolis force and its applications.
3. Motion under a Central Force, Kepler's Laws.
4. Gravitationa Law and Field. Potential due to spherical body
6. System of particles, Centre of mass, equation of motion.
7. Conservation of linear and angular Momenta, Conservation of Energy
11. Potential Well and periodic oscillations, case of harmonic oscillations
12. Differential equation and its solution, kinetic and potential energy.
24. E as deflecting field -CRO, sensitivity, fast CRO
25. Transverse B field, 180 o deflection, mass spectrograph or velocity selector.
28. Parallel E and B fields positive ray parabolas, discovery of isotopes.
29. Elements of mass spectrography,principles of magentic focussing (lens).
34. Bernoulli's theorem, viscious fluids, streamline and turbulent flow.
56. Capacitors, electrostatic field energy, force per unit area of the surface of a conductor in an electric field.
63. Rise and decay of LR and CR circuits, decay constants, transients in LCR circuits
64. AC circuits, complex numbers and their applications in solving ac circuit problems, complex impedance and,
reactance.
68. Force on a straight conductor carrying current of a uniform magnetic field,torque on a current loop, magnetic
dipole moment, angular mogmentum and gyromagnetic ratio.
70. Ampere's Law Field due to a magnetic dipole.
79. Waves in a conducting medium reflection and refraction by the ionosphere.
3. Motion under a Central Force, Kepler's Laws.
4. Gravitationa Law and Field. Potential due to spherical body
6. System of particles, Centre of mass, equation of motion.
7. Conservation of linear and angular Momenta, Conservation of Energy
11. Potential Well and periodic oscillations, case of harmonic oscillations
12. Differential equation and its solution, kinetic and potential energy.
24. E as deflecting field -CRO, sensitivity, fast CRO
25. Transverse B field, 180 o deflection, mass spectrograph or velocity selector.
28. Parallel E and B fields positive ray parabolas, discovery of isotopes.
29. Elements of mass spectrography,principles of magentic focussing (lens).
34. Bernoulli's theorem, viscious fluids, streamline and turbulent flow.
56. Capacitors, electrostatic field energy, force per unit area of the surface of a conductor in an electric field.
63. Rise and decay of LR and CR circuits, decay constants, transients in LCR circuits
64. AC circuits, complex numbers and their applications in solving ac circuit problems, complex impedance and,
reactance.
68. Force on a straight conductor carrying current of a uniform magnetic field,torque on a current loop, magnetic
dipole moment, angular mogmentum and gyromagnetic ratio.
70. Ampere's Law Field due to a magnetic dipole.
79. Waves in a conducting medium reflection and refraction by the ionosphere.
Thursday, November 11, 2010
4 gravitational law and field, potential due to a spherical body
4 gravitational law and field, potential due to a spherical body
2 uniformly rotating frame, centripetal force, CORIOLIS force and its applications
2 uniformly rotating frame, centripetal accelaration, CORIOLIS force and its applications
3 motion under a central force, kepler's laws
3 motion under a central force, kepler's laws
When the force acting on a particle is always directed towards a fixed point, the motion is called central force motion.
This type of motion is particularly relevant when studying the orbital movement of planets and satellites.
The laws which govern this motion were first postulated by Kepler around 1630 and deduced from observation. Later when Newton enunciated his theory of gravitation and laws of motion, it was possible to deduce the characteristics of central force motion from Newton's Laws.
Before Kepler, another astronomer Copernicus had first stated around 1540 that the universe is not earth-centric but sun-centric and it is the earth that moves around the sun and not vice-versa as was the belief. But this idea had not caught momentum. Only after Kepler's observations and postulates and mathematical deduction that tallied with observation about planetary motion that this was accepted.
The simplest center-force motion is obviously the uniform circular motion of a particle around a fixed center. We learn about such motion under "centripetal force". Let us complicate that study by bringing in two factors. First, imagine two bodies of masses M1 and M2 which are moving with respect to each other. It can be shown that their motion is equivalent to the motion of their center of mass. Thus we can reduce a two-body-motion problem to a one-body-motion problem, thus partly reducing the complication. Further, if we have a very large body at the center and a tiny mass moving round it. Then M1 >> M2, so the system will behave as if first mass is stationary and the center of mass is at same position as that of M1. This model was useful for Kepler as he was trying to study the motion of planets around the sun, whose mass and size is very large wrt that of planets. Later we can go to a slightly complicated situation where masses of the two bodies are comparable to each other.
The second complication can be brought in by considering a path which is not circular but elliptical. Kepler postulated from various astronomical observations that the planetary path around the sun was elliptical. It is interesting to note that the two body problem was studied by Kepler (1571-1630) well before Newton was born. Kepler postulated the following 3 laws:
1.- The orbits of the planets are ellipses with the Sun at one focus
2.- The line joining a planet to the Sun sweeps out equal areas in equal intervals of time
3.- The square of the period of a planet is proportional to the cube of the major axis of its elliptical orbit.
Then comes the issue of force. The planetary motion is result of some force, which will obviously be less for far away planets. Applying Newton's law of Gravitation, the force is inversely proportional to square of distance.
we have F = - k by r square into vector e where vector e is a unit vector along the line between the sun and the planet.. The - sign indicates that the force is attractive but a generalisation can be made to include repulsive force also (k>0).
The corresponding scalar potential (the potential energy of the planet) is:
V(r) = k by r
Equations of Motion
The equation of motion (F = ma), is
------------
Since the only force in the system is directed towards point O, the angular momentum of m with respect
to the origin will be constant. Therefore, the position and velocity vectors, r and rÿ , will be in a plane
4
Thursday, October 28, 2010
Overview of Atomic Physics in 20th century
Today we know quite a lot about the structure of atom -- we can use atoms in nuclear power plants for getting a supply of energy.
Let us see what were the broad developments during last 2 centuries which took us through to this stage.
Between 1770 to 1870 a lot of quantitative research was done by measuring, with help of accurate machines, the weight, volume, specific density, temp, pressure, vapour density etc.
Prominent scientists who experimented were Lavoisier, Charles, Boyle, Dalton, Gay-Lusaac, Avogadro, Victor Meyer, Mendeleev etc.
Lavoisier stated the first version of the law of conservation of mass, identified and named oxygen (1778) and hydrogen (1783) and later showed that they combined to form water. Charles and Boyle gave two gas laws about how the volume of gases changed with respect to temperature and pressure. Concept of vapour density was a method to tell how much a certain volume of gas was heavier than the same volume of hydrogen.
We have dalton's atomic theory to state 5 principles namely
1. All elements are made of a smallest unit of particles called ATOMS.
2. All atoms of a given element are identical but not the atoms of different elements - they differ in weights.
3. Atoms of one element can combine with a fixed number of atoms of other element to form chemical compounds; a given compound always has the same relative numbers of types of atoms.
4. Atoms cannot be created, divided into smaller particles, nor destroyed in the chemical process; a chemical reaction simply changes the way atoms are grouped together.
It was observed that whenever hydrogen and oxygen combined to form water, the weights of two gases consumed was always in the ratio of 1:8, the excess weights remaining unutilised. This is what led to the clause 3 above.
Avogadro could postulate that "equal volumes of gases at the same temperature and pressure contain the same number of molecules regardless of their chemical nature and physical properties". Dalton and Gay Lussac also tried to prepare list of all chemical elements arranged according to weight.
Victor Meyer developed an apparatus for quick and accurate measurement of vapour density -- which further told about molecular and atomic weight. Many elements were measured this way and their molecular weights were recorded. Mendeleev once again arranged all elements in according to their atomic weight but in an imaginative manner, he made use of their chemical property of valency too. He found that elements showed a periodicity of 8 valencies, so he arranged them in a table of 8 columns and several rows and assigned one cell to one element. Whenever there was a mismatch between atomic weight and valency, he was bold enough to treat valency as the right cue and predict some other explanation for the mismatch. This was a very useful concept and with few corrections, his table has now become the standard "Periodic Table".
Now we need to look at a totally different aspect. In 1855, Geissler invented the mercury displacement pump and achieved a record vacuum of about 10 Pa. A number of new properties of gases became observable at this vacuum level, leading in turn, to 3 important developments.Scientists rushed to take a long glass tube fitted inside with two metal-plate electrodes, create high vacuum inside and study the effect of high voltage-high vacuum. This apparatus came to be known as Cathode-ray tube.
We find Cathode-ray tube studies taking us to 3 new branches. First, there was discovery of X-rays in 1895 - it led to a new branch in physics for studying molecular structures, it revolutionized medical investigations and it won the very first Nobel Prize of Physics for Rontgen in 1901. second was construction of mass-spectrograph to accurately measure the atomic weights and third was development of vacuum tube which marked the beginning of electronics.
From the study of
Let us see what were the broad developments during last 2 centuries which took us through to this stage.
Between 1770 to 1870 a lot of quantitative research was done by measuring, with help of accurate machines, the weight, volume, specific density, temp, pressure, vapour density etc.
Prominent scientists who experimented were Lavoisier, Charles, Boyle, Dalton, Gay-Lusaac, Avogadro, Victor Meyer, Mendeleev etc.
Lavoisier stated the first version of the law of conservation of mass, identified and named oxygen (1778) and hydrogen (1783) and later showed that they combined to form water. Charles and Boyle gave two gas laws about how the volume of gases changed with respect to temperature and pressure. Concept of vapour density was a method to tell how much a certain volume of gas was heavier than the same volume of hydrogen.
We have dalton's atomic theory to state 5 principles namely
1. All elements are made of a smallest unit of particles called ATOMS.
2. All atoms of a given element are identical but not the atoms of different elements - they differ in weights.
3. Atoms of one element can combine with a fixed number of atoms of other element to form chemical compounds; a given compound always has the same relative numbers of types of atoms.
4. Atoms cannot be created, divided into smaller particles, nor destroyed in the chemical process; a chemical reaction simply changes the way atoms are grouped together.
It was observed that whenever hydrogen and oxygen combined to form water, the weights of two gases consumed was always in the ratio of 1:8, the excess weights remaining unutilised. This is what led to the clause 3 above.
Avogadro could postulate that "equal volumes of gases at the same temperature and pressure contain the same number of molecules regardless of their chemical nature and physical properties". Dalton and Gay Lussac also tried to prepare list of all chemical elements arranged according to weight.
Victor Meyer developed an apparatus for quick and accurate measurement of vapour density -- which further told about molecular and atomic weight. Many elements were measured this way and their molecular weights were recorded. Mendeleev once again arranged all elements in according to their atomic weight but in an imaginative manner, he made use of their chemical property of valency too. He found that elements showed a periodicity of 8 valencies, so he arranged them in a table of 8 columns and several rows and assigned one cell to one element. Whenever there was a mismatch between atomic weight and valency, he was bold enough to treat valency as the right cue and predict some other explanation for the mismatch. This was a very useful concept and with few corrections, his table has now become the standard "Periodic Table".
Now we need to look at a totally different aspect. In 1855, Geissler invented the mercury displacement pump and achieved a record vacuum of about 10 Pa. A number of new properties of gases became observable at this vacuum level, leading in turn, to 3 important developments.Scientists rushed to take a long glass tube fitted inside with two metal-plate electrodes, create high vacuum inside and study the effect of high voltage-high vacuum. This apparatus came to be known as Cathode-ray tube.
We find Cathode-ray tube studies taking us to 3 new branches. First, there was discovery of X-rays in 1895 - it led to a new branch in physics for studying molecular structures, it revolutionized medical investigations and it won the very first Nobel Prize of Physics for Rontgen in 1901. second was construction of mass-spectrograph to accurately measure the atomic weights and third was development of vacuum tube which marked the beginning of electronics.
From the study of
Wednesday, October 27, 2010
DC Generator and Motor AC G & M
Generators and Motors
Consider two poles of a magnet between which a rectangular coil of wire is rotated by using mechanical energy. This is an Electrical generator in which the varying magnetic field will create an electric field due to electromagnetic induction, which in turn will generate emf between generator terminals.
In a DC generator, the two ends of the coil are joined to two split-rings which are insulated from each other and from the central shaft. Two collecting brushes (of carbon or copper) press against the slip rings. The special arrangement of brushes and slips allows to gather the emf on the terminals. Charge separation takes place due to electrons flowing away from one terminal and toward the other, until, in the open-circuit case, sufficient electric field builds up to make further movement unfavorable. The emf is countered by the electrical voltage due to charge separation. If a load is attached, this voltage can drive a current.
A motor
A motor is essentially same arrangement as a generartor.
If an Electric current flows through the coil, one side will experience an upward force while the other will experience a downward force, causing the loop to turn by 90 degrees and come to rest. The loop can be made to spin (or rotate ???) continuously by fixing a half circle of copper known as commutator, to each end of the loop. Current is passed into and out of the loop by brushes that press onto the strips. The brushes do not go round so the wire of the loop does not get twisted. This arrangement makes sure that the current always passes down on the right side and back on the left side so that the rotation continues. This is how a simple Electric motor is made.
When we use mechanical power to move the coil and generate emf on the terminals, it is a generator. But if we use a DC voltage supply as input, the contacts at the brushes will make the coil to rotate, which will create mechanical motion. As the motor is turning, it also acts as a generator and generates a "back emf". By Lenz's law, the emf generated by the motor coil will oppose the change that created it. If the motor is not driving a load, then the generated back emf will almost balance the input voltage and very little current will flow in the coil of the motor. But if the motor is driving a heavy load, the back emf will be less and more current will flow in the motor coil. Thus electric power being used is converted to the mechanical power to drive the load. The motors inside all domestic appliances which we see daily such as a fan, rotor, grinding machine etc are essentially such motors.
AC Generator and Motor
A hand-cranked generator can be used to generate voltage which in turn can run a motor. This is an example of energy conversion from mechanical to electrical energy and then back to mechanical energy.
The turning of a coil in a magnetic field produces motional emfs in both sides of the coil which add. Since the component of the velocity perpendicular to the magnetic field changes sinusoidally with the rotation, the generated voltage is sinusoidal or AC.
As the motor is turning, it also acts as a generator and generates a "back emf". By Lenz's law, the emf generated by the motor coil will oppose the change that created it. If the motor is not driving a load, then the generated back emf will almost balance the input voltage and very little current will flow in the coil of the motor. But if the motor is driving a heavy load, the back emf will be less and more current will flow in the motor coil and that electric power is converted to the mechanical power to drive the load.
Mutual Inductance
When two coils are placed nearby, a change in current through one will change the magnetic flux and such a change will induce a current in the second coil. But the current in the second coil also being changing will have a reciprocal effect on the current in first coil. This is called mutual inductance.
Imagine two coils wound on two arms of a core made of iron which allows smooth passage of magnetic flux. If an AC current is passed through one coil, called primary winding, then an AC current will be generated in the second coil. If the no of loops in the secondary winding is less then the voltage generated across the coil will also be less. But the current generated will increase such that the power in first coil is same as the power in second coil (neglecting small energy losses in the system). This is called transformer and depending on whether voltage in secondary circuit is less or more it is called step-down or step-up transformer.
Thus transformer is a unique way of transferring electric power from one system to another. This is used for power transmission. You step up the power, thus increasing voltage but reducing current. Then when you transmit the power, ohmic losses will be less as the current is low. At the other end you use a step down transformer to get a normal voltage of 220 volts. This is why transmission is done by high tension wires that is, wires carrying a very high voltage current.
Self induction –
Just as current is induced in the second coil kept nearby, similarly a voltage is also generated in the wire which carries the verying current because the changing magnetic flux has impact on the wire too. This is called Self inductance. The induced emf will tend to oppose the current which created it. Net effect is some kind of resistance to the current which is called inductive resistance as opposed to ohmic resistance. In circuit diagrams the inductive resistance is shown as a coil.
The voltage generated by self induction due to verying current can be written as
Where
VL = the induced voltage in volts
L = the value of inductance in henries
di/dt = the rate of change of current in amperes per second.
The term inductor is used to describe a circuit element possessing the property of inductance and a coil of wire is a very common inductor. In circuit diagrams, a coil or wire is usually used to indicate an inductive component.
Consider two poles of a magnet between which a rectangular coil of wire is rotated by using mechanical energy. This is an Electrical generator in which the varying magnetic field will create an electric field due to electromagnetic induction, which in turn will generate emf between generator terminals.
In a DC generator, the two ends of the coil are joined to two split-rings which are insulated from each other and from the central shaft. Two collecting brushes (of carbon or copper) press against the slip rings. The special arrangement of brushes and slips allows to gather the emf on the terminals. Charge separation takes place due to electrons flowing away from one terminal and toward the other, until, in the open-circuit case, sufficient electric field builds up to make further movement unfavorable. The emf is countered by the electrical voltage due to charge separation. If a load is attached, this voltage can drive a current.
A motor
A motor is essentially same arrangement as a generartor.
If an Electric current flows through the coil, one side will experience an upward force while the other will experience a downward force, causing the loop to turn by 90 degrees and come to rest. The loop can be made to spin (or rotate ???) continuously by fixing a half circle of copper known as commutator, to each end of the loop. Current is passed into and out of the loop by brushes that press onto the strips. The brushes do not go round so the wire of the loop does not get twisted. This arrangement makes sure that the current always passes down on the right side and back on the left side so that the rotation continues. This is how a simple Electric motor is made.
When we use mechanical power to move the coil and generate emf on the terminals, it is a generator. But if we use a DC voltage supply as input, the contacts at the brushes will make the coil to rotate, which will create mechanical motion. As the motor is turning, it also acts as a generator and generates a "back emf". By Lenz's law, the emf generated by the motor coil will oppose the change that created it. If the motor is not driving a load, then the generated back emf will almost balance the input voltage and very little current will flow in the coil of the motor. But if the motor is driving a heavy load, the back emf will be less and more current will flow in the motor coil. Thus electric power being used is converted to the mechanical power to drive the load. The motors inside all domestic appliances which we see daily such as a fan, rotor, grinding machine etc are essentially such motors.
AC Generator and Motor
A hand-cranked generator can be used to generate voltage which in turn can run a motor. This is an example of energy conversion from mechanical to electrical energy and then back to mechanical energy.
The turning of a coil in a magnetic field produces motional emfs in both sides of the coil which add. Since the component of the velocity perpendicular to the magnetic field changes sinusoidally with the rotation, the generated voltage is sinusoidal or AC.
As the motor is turning, it also acts as a generator and generates a "back emf". By Lenz's law, the emf generated by the motor coil will oppose the change that created it. If the motor is not driving a load, then the generated back emf will almost balance the input voltage and very little current will flow in the coil of the motor. But if the motor is driving a heavy load, the back emf will be less and more current will flow in the motor coil and that electric power is converted to the mechanical power to drive the load.
Mutual Inductance
When two coils are placed nearby, a change in current through one will change the magnetic flux and such a change will induce a current in the second coil. But the current in the second coil also being changing will have a reciprocal effect on the current in first coil. This is called mutual inductance.
Imagine two coils wound on two arms of a core made of iron which allows smooth passage of magnetic flux. If an AC current is passed through one coil, called primary winding, then an AC current will be generated in the second coil. If the no of loops in the secondary winding is less then the voltage generated across the coil will also be less. But the current generated will increase such that the power in first coil is same as the power in second coil (neglecting small energy losses in the system). This is called transformer and depending on whether voltage in secondary circuit is less or more it is called step-down or step-up transformer.
Thus transformer is a unique way of transferring electric power from one system to another. This is used for power transmission. You step up the power, thus increasing voltage but reducing current. Then when you transmit the power, ohmic losses will be less as the current is low. At the other end you use a step down transformer to get a normal voltage of 220 volts. This is why transmission is done by high tension wires that is, wires carrying a very high voltage current.
Self induction –
Just as current is induced in the second coil kept nearby, similarly a voltage is also generated in the wire which carries the verying current because the changing magnetic flux has impact on the wire too. This is called Self inductance. The induced emf will tend to oppose the current which created it. Net effect is some kind of resistance to the current which is called inductive resistance as opposed to ohmic resistance. In circuit diagrams the inductive resistance is shown as a coil.
The voltage generated by self induction due to verying current can be written as
Where
VL = the induced voltage in volts
L = the value of inductance in henries
di/dt = the rate of change of current in amperes per second.
The term inductor is used to describe a circuit element possessing the property of inductance and a coil of wire is a very common inductor. In circuit diagrams, a coil or wire is usually used to indicate an inductive component.
Friday, October 22, 2010
EMF, EMI and Faraday’s Laws of EMI
EMF, EMI and Faraday’s Laws of EMI
EMF, EMI and Faraday’s Laws of EMI
Today we are going to learn about EMF, that is Electro motive Force, EMI, that is Electro Magnetic Induction and Faraday’s Laws of ElectroMagnetic Induction.
Broadly, Electromotive Force is the force that moves an electric charge. Such motion is a current. Discovery of current was as important for progress of human society as the discovery of Fire thousands of years back or the construction of a steam engine by James Watt. Current electricity was the newest method of dealing with power and energy in the nineteenth century that made two things possible, -- first to instantly switch power on and off and later to transfer power to distant places -- this was something unknown before. Both these possibilities have greatly transformed the human life style.
Elecro Motive Force can be provided by various devices like voltaic cells, thermoelectric devices, solar cells and the fuel cell.
Another completely different source of EMF is the phenomenon of electromagnetic induction which is used in electrical generators, transformers, and electrical motors.
Volta’s pile
Let us briefly see the historical context. In 1800, nearly 210 years back, Volta created the historic Voltaic pile.
Taking clue from Galvani’s experiments, he arranged several pairs of alternating copper and zinc discs which he called electrodes in a pile. All discs were separated by cloth soaked in brine which served as electrolyte conductor to increase the conductivity inside the pile. When he connected the top and bottom discs by a wire, an electric current flowed through the wire.
The strength of such pile is expressed in terms of electromotive force, or EMF, whose unit is volts. You have guessed it right that the name of unit of EMF is in honour of Volta. Volta also measured the characteristic EMF of different pairs of metals in place of Cu and Zn. We now understand that the phenomenon in the voltaic piles or their refined mode, the household battery. The electric potential difference is created by separation of positive and negative charges, as a result of chemical reaction between electrodes and electrolyte.
Being a ‘potential ’, an EMF can drive a unit charge. Outside the circuit it will drive the charge from an electrical terminal with a higher potential to another terminal with a lower potential to do an amount of work. This idea is like pumping water up into a tank, from where it can be distributed from high to low potential. However, first the pump has to push water from lower to higher potential, that is, do some work. Similarly, inside the cell, work will be done and the electric charge will be pushed from lower to higher potential.
Let us therefore define EMF as the external work done per unit of charge leading to an electric potential difference across two terminals of a battery, or some such apparatus.Thus,
E = dW/dq
The electrical potential difference thus created would cause the current if an external circuit is attached to the source of emf.
Inside the cell, the chemical reaction will push a positive charge from a point of low potential to a point of high potential. And in the process, will performs work dW on that charge to move it to the high potential terminal.
In the open-circuit case, the reactions at the electrode–electrolyte interfaces will continue to separate the charges and to provide the EMF until the electrostatic field from the separated charges is sufficient to arrest the flow of incoming charges. This is why an open circuit battery will not drain out early. That is also why it is recommended to open the battery in cars when you know that the car is not likely to be used for a long time.
• The overall electrochemical cell reaction can be written as 2 half-equations:
1 equation for the reduction reaction where electron are gained and 1 equation for the oxidation reaction in which electrons are given away.
• The number of electrons gained in the reduction half reaction must equal the number of electrons lost in the oxidation half reaction
• However since the elements of the electrode pair are different, the internal energy level of the element giving away the electron is different than the internal energy of the element accepting them. This is the source of energy inside the cell which makes possible the (internal) pushing of charge from the lower-potential-terminal to the higher-potential-terminal. The higher the energy per reacting charge (electron), the higher the potential it can be pushed to, before the reaction reaches an equilibrium with the EMF, and stops.
• The cell's emf is calculated by adding together the E values for each half reaction:
Ecell = Ereduction + Eoxidation
• As the cell operates, the reactants are used up causing the emf to decrease.
• Following are some typical half electrode potentials --
K+ + e -2.92 V
Al3+ + 3e -1.66 V
Zn2+ +2e - 0.76 V
Ni2+ +2e - 0.23 V
Cu2+ +2e + 0.34 V
Ag+ +e + 0.80 V
Thus a typical Cu-Zn cell will give emf of 1.10 V whereas Ag-Zn cell will give 1.56 V and Cu-Al will give 2.00 V
Some modern sources of emf are a solar cell or photodiode which uses light as the external source of energy. In thermionic emissions it is the thermal energy and in fuel cell it is again the chemical energy.
----------------------------------------------------------------------------------------
EMI
Having understood this much about emf and Volta’s batteries, we come to the most interesting consequential development out of them, namely the discovery of electromagnetic induction by Faraday in 1831. We can recall that though static electricity and magnetism were known to humanity for many decades, the discovery of CURRENT was new and many scientists rushed to experiment with it. Among them, Oersted had observed and reported that a magnetic needle kept near a current switch flickered when the current was either switched on or off. So if a current can influence a magnet, will not a magnet influence the current?
Faraday observed that whenever the magnetic flux changes, it gives rise to a current – meaning that a changing magnetic flux is a source of emf.
Now magnetic flux can be changed either by moving a magnet, say inside the coil of a metallic conductor or by moving the coil between two fixed magnetic poles.
In its simplest fom, Electro Magnetic Induction produces or induces a voltage across a conductor moving through a magnetic field.
The Faraday’s Laws of EMI states that:
The induced electromotive force (emf) in any closed circuit is equal to the rate of change of magnetic flux through the circuit.
In other words, in any closed circuit such as a loop of a wire, when the magnetic flux through a surface bounded by the conductor changes, there will be an induced emf and a resultant current.
A corollary from Faraday's Law was given by Lenz, which is analogous to Newton’s third law of action-reaction. Lenz's law says:
"An induced current is always in such a direction as to oppose the motion or change causing it"
Thus, for a loop we can write --
E = - dΦ /dt
E is the electromotive force (emf) in volts
Φ is the magnetic flux in webers
For the common but special case of a coil of wire, composed of N loops with the same area, Faraday's law of electromagnetic induction states that
E = - N.dΦ /dt
where N is the number of turns of wire
The opposion created by induced current gives the minus sign in the above equation.
If the rate of change of current in a circuit is one ampere per second and the resulting electromotive force is one volt, then the inductance of the circuit is one henry. The name henry was given to the unit of inductance in the honor of Henry, a contemporary scientist who also accomplished lot of studies on the subject.
What is the most significant aspect of Faraday’s discovery?
On application side, it tells us -- move a magnet and you can produce a current – thus we see that while Volta discovered how chemical energy is converted to electrical power, Faraday’s discovery was a way to convert mechanical energy into electrical power. This led to a whole range of generators, electric motors, transformers and a new branch named electrical engineering. As I earlier mentioned, unlike other known sources of power, the electrical power available in terms of current, could be transported to long distances and made available there. This had far-reaching consequences.
Let us learn about them.
In physics there is a trick to understand many phenomena -- always think in terms of the pair Effort and flow. Their product is power.
• Thus, when effort is FORCE, then flow is velocity and FxV = power
• when effort is EMF, the flow is current and VxI = power
• If Magnetic field is B, and length of conductor is l, and a current I is passed, then ,
• Conductor will experience a force = Bil
• and if velocity is v then power = Fv=Bilv
• On the other hand, if the emf generated across the conductor is E then by definition,
• E = Blv. And,
• Power = emf x current = Blvi
Just by remembering these concepts , you can understand a lot about power generation.
Electrical Generator and Motor
Consider two poles of a magnet between which a coil of wire is rotated by using mechanical energy. The two ends of the coil are joined to two split-rings which are insulated from each other and from the central shaft. Two collecting brushes (of carbon or copper) press against the slip rings. This is an Electrical generator because the varying magnetic field will create an electric field due to electromagnetic induction, which in turn will generate emf between generator terminals. The special arrangement of split-rings, brushes and slips allows to gather the emf on the terminals. Charge separation takes place due to electrons flowing away from one terminal and toward the other, until, in the open-circuit case, sufficient electric field builds up to make further movement unfavorable. Again the emf is countered by the electrical voltage due to charge separation, but when a load is attached, this voltage can drive a current.
A motor
A motor is essentially same arrangement as a generartor. When we use mechanical power to move the coil and generate emf on the terminals, it is a generator. But if we use a DC voltage supply as input, the contacts at the brushes will make the coil to rotate, which will create mechanical motion. As the motor is turning, it also acts as a generator and generates a "back emf". By Lenz's law, the emf generated by the motor coil will oppose the change that created it. If the motor is not driving a load, then the generated back emf will almost balance the input voltage and very little current will flow in the coil of the motor. But if the motor is driving a heavy load, the back emf will be less and more current will flow in the motor coil and that electric power being used is converted to the mechanical power to drive the load.The motors inside all domestic appliances which we see daily such as a fan, rotor, grinder etc work on this principle .
AC Generator and Motor
A hand-cranked generator can be used to generate AC voltage which will further turn a motor. This is an example of energy conversion from mechanical to electrical energy and then back to mechanical energy.
Mutual Inductance
When two coils are placed nearby, a change in current through one will change the magnetic flux and such a change will induce a current in the second coil. But the current in the second coil also being changing will have a reciprocal effect on the current in first coil. This is called mutual inductance.
Transformer
Imagine two coils wound on two arms of a core made of iron which allows smooth passage of magnetic flux. If an AC current is passed through one coil, called primary winding, then an AC current will be generated in the second coil. If the number of loops in the secondary winding is less, then the voltage generated across the coil will also be less. But the current generated will increase such that the power in first coil is same as the power in second coil except for negligible energy losses in the system. This is called transformer and depending on whether voltage in secondary circuit is less or more it is called step-down or step-up transformer.
Thus transformer is a unique way of transferring electric power from one system to another. This is used for power transmission. You step up the power, thus increasing voltage but reducing current. Then when you transmit the power, ohmic losses will be less as the current is low. At the other end you use a step down transformer to get a normal voltage of 220 volts. This is why transmission is done by high tension wires that is, wires carrying a very high voltage current.
Self induction –
Just as current is induced in the second coil kept nearby, similarly a voltage is also generated in the wire which carries the varying current because the changing magnetic flux has impact on the wire too. This is called Self inductance. The induced emf will tend to oppose the current which created it. Net effect is some kind of resistance to the current which is called inductive resistance as opposed to ohmic resistance.
The voltage generated by self induction due to verying current can be written as
V = L di/dt
Where
V = the induced voltage in volts
L = the value of inductance in henries
di/dt = the rate of change of current in amperes per second.
The term inductor is used to describe a circuit element possessing the property of inductance and a coil of wire is a very common inductor. In circuit diagrams, a coil or wire is usually used to indicate an inductive component.
Formal definitions of electromotive force
Inside a source of emf in open-circuit condition, the electrostatic field created by separation of charge exactly cancels the forces producing the emf. Thus, the emf has the same value but opposite sign as the integral of the electric field aligned with the internal path travelled by the charges between two terminals A and B. Mathematically ---
where Ecs is the electrostatic field created by the charge separation, dℓ is a small section of path from terminal A to terminal B. This equation applies only to locations A and B of the terminals and inside the source of emf. For the closed loop, the integral will be zero (???).
However if the closed path is in the presence of a varying magnetic field, then the integral of the electric field around the closed loop will be nonzero; because of the "induced emf"
Now The "induced emf" around a stationary closed path C is:
where now E is the entire electric field, conservative and non-conservative, and the integral is around an arbitrary but stationary closed curve C through which there is a varying magnetic field. We must remember that the electrostatic field does not contribute to the net emf around a circuit because the electrostatic portion of the electric field is conservative (that is, the work done against the field around a closed path is zero).
Hence for an arbitrary source of emf where flux is changing and path is also moving,
+ some correctional effect for chemical and Thermal forces.
----------------------------------------------------------------------------------------------------------------------
Maxwell's equations (cut paste) Faraday's experiments
The applied aspect of Faraday’s discovery of electromagnetic induction led to a new branch of electric engineering. But the theoretical study of it led to the invention of electromagnetic theory of light – that is how light, or more appropriately how energy travels as electromagnetic waves and this further led to the theory of relativity.
Faraday had tried to explain the phenomenon by conceptualising lines of force, and flux density. Let me remind you of a childhood pass time. You take two large pieces of broken bangle, hold the middle of one on a candle flame so that the glass bends till the two open ends meet. Then you weave another piece through this loop and again bend it on the flame at its middle section -- till its ends also meet. Thus you have two bangle loops woven into each other. This is what Faraday visualised as the loop of the conducting wire and the invisible loop of magnetic flux. This conceptualisation was very useful for developing the vector calculus to get mathematical expression for Electro magnetic Induction.
Through his equations—Maxwell demonstrated that electric and magnetic fields travel through space in the form of waves, and when he theoretically calculated the speed, he found it in the close range of the speed of light. He concluded that electricity, magnetism and even light are all manifestations of the same phenomenon, namely, the electromagnetic field. His quantitative connection between light and electromagnetism is considered one of the great accomplishments of 19th century mathematical physics.
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EMF, EMI and Faraday’s Laws of EMI
Today we are going to learn about EMF, that is Electro motive Force, EMI, that is Electro Magnetic Induction and Faraday’s Laws of ElectroMagnetic Induction.
Broadly, Electromotive Force is the force that moves an electric charge. Such motion is a current. Discovery of current was as important for progress of human society as the discovery of Fire thousands of years back or the construction of a steam engine by James Watt. Current electricity was the newest method of dealing with power and energy in the nineteenth century that made two things possible, -- first to instantly switch power on and off and later to transfer power to distant places -- this was something unknown before. Both these possibilities have greatly transformed the human life style.
Elecro Motive Force can be provided by various devices like voltaic cells, thermoelectric devices, solar cells and the fuel cell.
Another completely different source of EMF is the phenomenon of electromagnetic induction which is used in electrical generators, transformers, and electrical motors.
Volta’s pile
Let us briefly see the historical context. In 1800, nearly 210 years back, Volta created the historic Voltaic pile.
Taking clue from Galvani’s experiments, he arranged several pairs of alternating copper and zinc discs which he called electrodes in a pile. All discs were separated by cloth soaked in brine which served as electrolyte conductor to increase the conductivity inside the pile. When he connected the top and bottom discs by a wire, an electric current flowed through the wire.
The strength of such pile is expressed in terms of electromotive force, or EMF, whose unit is volts. You have guessed it right that the name of unit of EMF is in honour of Volta. Volta also measured the characteristic EMF of different pairs of metals in place of Cu and Zn. We now understand that the phenomenon in the voltaic piles or their refined mode, the household battery. The electric potential difference is created by separation of positive and negative charges, as a result of chemical reaction between electrodes and electrolyte.
Being a ‘potential ’, an EMF can drive a unit charge. Outside the circuit it will drive the charge from an electrical terminal with a higher potential to another terminal with a lower potential to do an amount of work. This idea is like pumping water up into a tank, from where it can be distributed from high to low potential. However, first the pump has to push water from lower to higher potential, that is, do some work. Similarly, inside the cell, work will be done and the electric charge will be pushed from lower to higher potential.
Let us therefore define EMF as the external work done per unit of charge leading to an electric potential difference across two terminals of a battery, or some such apparatus.Thus,
E = dW/dq
The electrical potential difference thus created would cause the current if an external circuit is attached to the source of emf.
Inside the cell, the chemical reaction will push a positive charge from a point of low potential to a point of high potential. And in the process, will performs work dW on that charge to move it to the high potential terminal.
In the open-circuit case, the reactions at the electrode–electrolyte interfaces will continue to separate the charges and to provide the EMF until the electrostatic field from the separated charges is sufficient to arrest the flow of incoming charges. This is why an open circuit battery will not drain out early. That is also why it is recommended to open the battery in cars when you know that the car is not likely to be used for a long time.
• The overall electrochemical cell reaction can be written as 2 half-equations:
1 equation for the reduction reaction where electron are gained and 1 equation for the oxidation reaction in which electrons are given away.
• The number of electrons gained in the reduction half reaction must equal the number of electrons lost in the oxidation half reaction
• However since the elements of the electrode pair are different, the internal energy level of the element giving away the electron is different than the internal energy of the element accepting them. This is the source of energy inside the cell which makes possible the (internal) pushing of charge from the lower-potential-terminal to the higher-potential-terminal. The higher the energy per reacting charge (electron), the higher the potential it can be pushed to, before the reaction reaches an equilibrium with the EMF, and stops.
• The cell's emf is calculated by adding together the E values for each half reaction:
Ecell = Ereduction + Eoxidation
• As the cell operates, the reactants are used up causing the emf to decrease.
• Following are some typical half electrode potentials --
K+ + e -2.92 V
Al3+ + 3e -1.66 V
Zn2+ +2e - 0.76 V
Ni2+ +2e - 0.23 V
Cu2+ +2e + 0.34 V
Ag+ +e + 0.80 V
Thus a typical Cu-Zn cell will give emf of 1.10 V whereas Ag-Zn cell will give 1.56 V and Cu-Al will give 2.00 V
Some modern sources of emf are a solar cell or photodiode which uses light as the external source of energy. In thermionic emissions it is the thermal energy and in fuel cell it is again the chemical energy.
----------------------------------------------------------------------------------------
EMI
Having understood this much about emf and Volta’s batteries, we come to the most interesting consequential development out of them, namely the discovery of electromagnetic induction by Faraday in 1831. We can recall that though static electricity and magnetism were known to humanity for many decades, the discovery of CURRENT was new and many scientists rushed to experiment with it. Among them, Oersted had observed and reported that a magnetic needle kept near a current switch flickered when the current was either switched on or off. So if a current can influence a magnet, will not a magnet influence the current?
Faraday observed that whenever the magnetic flux changes, it gives rise to a current – meaning that a changing magnetic flux is a source of emf.
Now magnetic flux can be changed either by moving a magnet, say inside the coil of a metallic conductor or by moving the coil between two fixed magnetic poles.
In its simplest fom, Electro Magnetic Induction produces or induces a voltage across a conductor moving through a magnetic field.
The Faraday’s Laws of EMI states that:
The induced electromotive force (emf) in any closed circuit is equal to the rate of change of magnetic flux through the circuit.
In other words, in any closed circuit such as a loop of a wire, when the magnetic flux through a surface bounded by the conductor changes, there will be an induced emf and a resultant current.
A corollary from Faraday's Law was given by Lenz, which is analogous to Newton’s third law of action-reaction. Lenz's law says:
"An induced current is always in such a direction as to oppose the motion or change causing it"
Thus, for a loop we can write --
E = - dΦ /dt
E is the electromotive force (emf) in volts
Φ is the magnetic flux in webers
For the common but special case of a coil of wire, composed of N loops with the same area, Faraday's law of electromagnetic induction states that
E = - N.dΦ /dt
where N is the number of turns of wire
The opposion created by induced current gives the minus sign in the above equation.
If the rate of change of current in a circuit is one ampere per second and the resulting electromotive force is one volt, then the inductance of the circuit is one henry. The name henry was given to the unit of inductance in the honor of Henry, a contemporary scientist who also accomplished lot of studies on the subject.
What is the most significant aspect of Faraday’s discovery?
On application side, it tells us -- move a magnet and you can produce a current – thus we see that while Volta discovered how chemical energy is converted to electrical power, Faraday’s discovery was a way to convert mechanical energy into electrical power. This led to a whole range of generators, electric motors, transformers and a new branch named electrical engineering. As I earlier mentioned, unlike other known sources of power, the electrical power available in terms of current, could be transported to long distances and made available there. This had far-reaching consequences.
Let us learn about them.
In physics there is a trick to understand many phenomena -- always think in terms of the pair Effort and flow. Their product is power.
• Thus, when effort is FORCE, then flow is velocity and FxV = power
• when effort is EMF, the flow is current and VxI = power
• If Magnetic field is B, and length of conductor is l, and a current I is passed, then ,
• Conductor will experience a force = Bil
• and if velocity is v then power = Fv=Bilv
• On the other hand, if the emf generated across the conductor is E then by definition,
• E = Blv. And,
• Power = emf x current = Blvi
Just by remembering these concepts , you can understand a lot about power generation.
Electrical Generator and Motor
Consider two poles of a magnet between which a coil of wire is rotated by using mechanical energy. The two ends of the coil are joined to two split-rings which are insulated from each other and from the central shaft. Two collecting brushes (of carbon or copper) press against the slip rings. This is an Electrical generator because the varying magnetic field will create an electric field due to electromagnetic induction, which in turn will generate emf between generator terminals. The special arrangement of split-rings, brushes and slips allows to gather the emf on the terminals. Charge separation takes place due to electrons flowing away from one terminal and toward the other, until, in the open-circuit case, sufficient electric field builds up to make further movement unfavorable. Again the emf is countered by the electrical voltage due to charge separation, but when a load is attached, this voltage can drive a current.
A motor
A motor is essentially same arrangement as a generartor. When we use mechanical power to move the coil and generate emf on the terminals, it is a generator. But if we use a DC voltage supply as input, the contacts at the brushes will make the coil to rotate, which will create mechanical motion. As the motor is turning, it also acts as a generator and generates a "back emf". By Lenz's law, the emf generated by the motor coil will oppose the change that created it. If the motor is not driving a load, then the generated back emf will almost balance the input voltage and very little current will flow in the coil of the motor. But if the motor is driving a heavy load, the back emf will be less and more current will flow in the motor coil and that electric power being used is converted to the mechanical power to drive the load.The motors inside all domestic appliances which we see daily such as a fan, rotor, grinder etc work on this principle .
AC Generator and Motor
A hand-cranked generator can be used to generate AC voltage which will further turn a motor. This is an example of energy conversion from mechanical to electrical energy and then back to mechanical energy.
Mutual Inductance
When two coils are placed nearby, a change in current through one will change the magnetic flux and such a change will induce a current in the second coil. But the current in the second coil also being changing will have a reciprocal effect on the current in first coil. This is called mutual inductance.
Transformer
Imagine two coils wound on two arms of a core made of iron which allows smooth passage of magnetic flux. If an AC current is passed through one coil, called primary winding, then an AC current will be generated in the second coil. If the number of loops in the secondary winding is less, then the voltage generated across the coil will also be less. But the current generated will increase such that the power in first coil is same as the power in second coil except for negligible energy losses in the system. This is called transformer and depending on whether voltage in secondary circuit is less or more it is called step-down or step-up transformer.
Thus transformer is a unique way of transferring electric power from one system to another. This is used for power transmission. You step up the power, thus increasing voltage but reducing current. Then when you transmit the power, ohmic losses will be less as the current is low. At the other end you use a step down transformer to get a normal voltage of 220 volts. This is why transmission is done by high tension wires that is, wires carrying a very high voltage current.
Self induction –
Just as current is induced in the second coil kept nearby, similarly a voltage is also generated in the wire which carries the varying current because the changing magnetic flux has impact on the wire too. This is called Self inductance. The induced emf will tend to oppose the current which created it. Net effect is some kind of resistance to the current which is called inductive resistance as opposed to ohmic resistance.
The voltage generated by self induction due to verying current can be written as
V = L di/dt
Where
V = the induced voltage in volts
L = the value of inductance in henries
di/dt = the rate of change of current in amperes per second.
The term inductor is used to describe a circuit element possessing the property of inductance and a coil of wire is a very common inductor. In circuit diagrams, a coil or wire is usually used to indicate an inductive component.
Formal definitions of electromotive force
Inside a source of emf in open-circuit condition, the electrostatic field created by separation of charge exactly cancels the forces producing the emf. Thus, the emf has the same value but opposite sign as the integral of the electric field aligned with the internal path travelled by the charges between two terminals A and B. Mathematically ---
where Ecs is the electrostatic field created by the charge separation, dℓ is a small section of path from terminal A to terminal B. This equation applies only to locations A and B of the terminals and inside the source of emf. For the closed loop, the integral will be zero (???).
However if the closed path is in the presence of a varying magnetic field, then the integral of the electric field around the closed loop will be nonzero; because of the "induced emf"
Now The "induced emf" around a stationary closed path C is:
where now E is the entire electric field, conservative and non-conservative, and the integral is around an arbitrary but stationary closed curve C through which there is a varying magnetic field. We must remember that the electrostatic field does not contribute to the net emf around a circuit because the electrostatic portion of the electric field is conservative (that is, the work done against the field around a closed path is zero).
Hence for an arbitrary source of emf where flux is changing and path is also moving,
+ some correctional effect for chemical and Thermal forces.
----------------------------------------------------------------------------------------------------------------------
Maxwell's equations (cut paste) Faraday's experiments
The applied aspect of Faraday’s discovery of electromagnetic induction led to a new branch of electric engineering. But the theoretical study of it led to the invention of electromagnetic theory of light – that is how light, or more appropriately how energy travels as electromagnetic waves and this further led to the theory of relativity.
Faraday had tried to explain the phenomenon by conceptualising lines of force, and flux density. Let me remind you of a childhood pass time. You take two large pieces of broken bangle, hold the middle of one on a candle flame so that the glass bends till the two open ends meet. Then you weave another piece through this loop and again bend it on the flame at its middle section -- till its ends also meet. Thus you have two bangle loops woven into each other. This is what Faraday visualised as the loop of the conducting wire and the invisible loop of magnetic flux. This conceptualisation was very useful for developing the vector calculus to get mathematical expression for Electro magnetic Induction.
Through his equations—Maxwell demonstrated that electric and magnetic fields travel through space in the form of waves, and when he theoretically calculated the speed, he found it in the close range of the speed of light. He concluded that electricity, magnetism and even light are all manifestations of the same phenomenon, namely, the electromagnetic field. His quantitative connection between light and electromagnetism is considered one of the great accomplishments of 19th century mathematical physics.
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Monday, August 30, 2010
Thursday, August 19, 2010
ch 1, ch ३ तक -- संगणक क्या है , संगणक यंत्र है -done
भाग - 1
संगणक क्या है
आजकल संगणक शब्दसे कौन अनजान है? कईयोंने इसे देखा है और कईयोंने इसपर काम भी किया है। फिर भी किसीसे अचानक पूछो कि संगणक क्या है, तो वह गडबडायेगा जरूर। और इसपर काम करनेके विषय में भी कई भ्रांतियाँ हैं। जिन लोगोंने इसे देखा उनमेंसे पचास प्रतिशत कह उठते हैं कि भैया, ये तो अपने बसका नही., अन्य कई समझते हैं कि इसे खरीदना अपनी जेबपर भारी पडेगा। फिर जिन्होंने संगणकपर सुविधासे काम करना सीख लिया वे हँसते हैं -- "अरे, यह तो बडा ही सरल है।"
अर्थात् संगणक ऐसी वस्तु है जिसे एक ही समय कोई कठिन कहेगा तो कोई सरल, कोई कहेगा निरर्थक खर्चा तो कोई कहेगा सार्थक। और हाँ, उनके बुद्धिमान होने न होनेका इन मतोंसे कोई संबंध नही है।
-------------------------------------------
भाग - 2
संगणक यंत्र है
दरअसल संगणक एक यंत्र है
है ना सरलसी बात? संगणक की सबसे पहली पहचान यही है कि यह एक यंत्र है। दिनभरमें तुम कितने यंत्र देखते होगे।सायकल यंत्र है - पैडल मारनेसे चलती है और हमें यहाँ-वहाँ घुमाती है। घडी भी यंत्र है जो चाबी या बैटरी पर चलती है ओर समय बताती है। फ्रिज, टीवी, मोबाईल, लिफ्ट, कार, पम्प, ये सब यंत्र हैं।
गाँवके कुओंपर चलनेवाले रहट, बोअरवेल और उसका हॅण्डपम्प, स्प्रिंकलर, स्प्रे पम्प, आटेकी चक्की, ट्रॅक्टर, ये सभी यंत्र है। लेकिन संगणक एक जादूगर यंत्र है। क्योंकि उसके पास एक मस्तिष्क हैं.-- अब है तो वह भी यांत्रिक मस्तिष्क, पर मस्तिष्क है तो मस्तिष्ककी महत्ता भी रखता है। विभिन्न प्रकारके काम कर लेता है। अन्य यंत्रोंकी तरह नही कि एक ही काम कर सके। संगणक लिख सकता है, पढता है, गाने सुनाता है, फिल्म दिखाता है, फिल्म बनाता है, चित्र आँकता है, हमारे साथ खेलता है, दुनियाके एक कोनेसे दूसरे कोनेतक पलभरमें संदेश पहुँचाता है और हाँ, बडे-बडे गणित सुलझाता है, और चाँदतक पहुँचनेमें हमारी मदद भी करता है। इसीलिये यह सीधासादा नही बल्कि जादूगर यंत्र है।
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संगणक क्या है
आजकल संगणक शब्दसे कौन अनजान है? कईयोंने इसे देखा है और कईयोंने इसपर काम भी किया है। फिर भी किसीसे अचानक पूछो कि संगणक क्या है, तो वह गडबडायेगा जरूर। और इसपर काम करनेके विषय में भी कई भ्रांतियाँ हैं। जिन लोगोंने इसे देखा उनमेंसे पचास प्रतिशत कह उठते हैं कि भैया, ये तो अपने बसका नही., अन्य कई समझते हैं कि इसे खरीदना अपनी जेबपर भारी पडेगा। फिर जिन्होंने संगणकपर सुविधासे काम करना सीख लिया वे हँसते हैं -- "अरे, यह तो बडा ही सरल है।"
अर्थात् संगणक ऐसी वस्तु है जिसे एक ही समय कोई कठिन कहेगा तो कोई सरल, कोई कहेगा निरर्थक खर्चा तो कोई कहेगा सार्थक। और हाँ, उनके बुद्धिमान होने न होनेका इन मतोंसे कोई संबंध नही है।
-------------------------------------------
भाग - 2
संगणक यंत्र है
दरअसल संगणक एक यंत्र है
है ना सरलसी बात? संगणक की सबसे पहली पहचान यही है कि यह एक यंत्र है। दिनभरमें तुम कितने यंत्र देखते होगे।सायकल यंत्र है - पैडल मारनेसे चलती है और हमें यहाँ-वहाँ घुमाती है। घडी भी यंत्र है जो चाबी या बैटरी पर चलती है ओर समय बताती है। फ्रिज, टीवी, मोबाईल, लिफ्ट, कार, पम्प, ये सब यंत्र हैं।
गाँवके कुओंपर चलनेवाले रहट, बोअरवेल और उसका हॅण्डपम्प, स्प्रिंकलर, स्प्रे पम्प, आटेकी चक्की, ट्रॅक्टर, ये सभी यंत्र है। लेकिन संगणक एक जादूगर यंत्र है। क्योंकि उसके पास एक मस्तिष्क हैं.-- अब है तो वह भी यांत्रिक मस्तिष्क, पर मस्तिष्क है तो मस्तिष्ककी महत्ता भी रखता है। विभिन्न प्रकारके काम कर लेता है। अन्य यंत्रोंकी तरह नही कि एक ही काम कर सके। संगणक लिख सकता है, पढता है, गाने सुनाता है, फिल्म दिखाता है, फिल्म बनाता है, चित्र आँकता है, हमारे साथ खेलता है, दुनियाके एक कोनेसे दूसरे कोनेतक पलभरमें संदेश पहुँचाता है और हाँ, बडे-बडे गणित सुलझाता है, और चाँदतक पहुँचनेमें हमारी मदद भी करता है। इसीलिये यह सीधासादा नही बल्कि जादूगर यंत्र है।
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भाग
-
1
संगणक
क्या
है
आजकल
संगणक
शब्दसे
कौन
अनजान
है?
कईयोंने
इसे
देखा
है
और
कईयोंने
इसपर
काम
भी
किया
है।
फिर
भी
किसीसे
अचानक
पूछो
कि
संगणक
क्या
है,
तो
वह
गडबडायेगा
जरूर।
और
इसपर
काम
करनेके
विषय
में
भी
कई
भ्रांतियाँ
हैं।
जिन
लोगोंने
इसे
देखा
उनमेंसे
पचास
प्रतिशत
कह
उठते
हैं
कि
भैया,
ये
तो
अपने
बसका
नही.,
अन्य
कई
समझते
हैं
कि
इसे
खरीदना
अपनी
जेबपर
भारी
पडेगा।
फिर
जिन्होंने
संगणकपर
सुविधासे
काम
करना
सीख
लिया
वे
हँसते
हैं
--
"अरे,
यह
तो
बडा
ही
सरल
है।"
अर्थात्
संगणक
ऐसी
वस्तु
है
जिसे
एक
ही
समय
कोई
कठिन
कहेगा
तो
कोई
सरल,
कोई
कहेगा
निरर्थक
खर्चा
तो
कोई
कहेगा
सार्थक।
और
हाँ,
उनके
बुद्धिमान
होने
न
होनेका
इन
मतोंसे
कोई
संबंध
नही
है।
----------------------------
भाग
-
2
संगणक
यंत्र
है
दरअसल
संगणक
एक
यंत्र
है
है
ना
सरलसी
बात?
संगणक
की
सबसे
पहली
पहचान
यही
है
कि
यह
एक
यंत्र
है।
दिनभरमें
तुम
कितने
यंत्र
देखते
होगे।सायकल
यंत्र
है
-
पैडल
मारनेसे
चलती
है
और
हमें
यहाँ-वहाँ
घुमाती
है।
घडी
भी
यंत्र
है
जो
चाबी
या
बैटरी
पर
चलती
है
ओर
समय
बताती
है।
फ्रिज,
टीवी,
मोबाईल,
लिफ्ट,
कार,
पम्प,
ये
सब
यंत्र
हैं।
गाँवके
कुओंपर
चलनेवाले
रहट,
बोअरवेल
और
उसका
हॅण्डपम्प,
स्प्रिंकलर,
स्प्रे
पम्प,
आटेकी
चक्की,
ट्रॅक्टर,
ये
सभी
यंत्र
है।
लेकिन
संगणक
एक
जादूगर
यंत्र
है।
क्योंकि
उसके
पास
एक
मस्तिष्क
हैं.--
अब
है
तो
वह
भी
यांत्रिक
मस्तिष्क,
पर
मस्तिष्क
है
तो
मस्तिष्ककी
महत्ता
भी
रखता
है।
विभिन्न
प्रकारके
काम
कर
लेता
है।
अन्य
यंत्रोंकी
तरह
नही
कि
एक
ही
काम
कर
सके।
संगणक
लिख
सकता
है,
पढता
है,
गाने
सुनाता
है,
फिल्म
दिखाता
है,
फिल्म
बनाता
है,
चित्र
आँकता
है,
हमारे
साथ
खेलता
है,
दुनियाके
एक
कोनेसे
दूसरे
कोनेतक
पलभरमें
संदेश
पहुँचाता
है
और
हाँ,
बडे-बडे
गणित
सुलझाता
है,
और
चाँदतक
पहुँचनेमें
हमारी
मदद
भी
करता
है।
इसीलिये
यह
सीधासादा
नही
बल्कि
जादूगर
यंत्र
है।
भाग
-
३
संगणक
है
युक्तिभरा
जादूगर
यंत्र
संगणक
है
युक्तियों
भरा
जादूगर
यंत्र
।
लेकिन
कई
बार
लोगोंको
इससे
डर
लगता
है
उन्हें
लगता
है
,
कि
वे
कोई
गलत
बटन
दबा
देंगे
और
बडा
अनर्थ
हो
जायेगा।
तो
सबसे
पहले
हमे
समझ
लेना
चाहिये
कि
संगणक
का
कोई
बटन
दब
गया
और
उसमें
कोई
गडबडी
हुई
ऐसा
साधारणतया
कम
ही
होता
है।
प्रायः
नही
हे
बराबर!
डरने
का
दूसरा
कारण
यह
है
कि
संगणक
का
हर
काम
एक
खास
तरीके
से
या
खास
क्रम
से
होता
है।
जहाँ
हमसे
उस
क्रम
में
जरा
सी
भी
चूक
हुई
कि
संगणक
अडियल
टट्टूकी
तरह
अड
जाता
है।
फिर
वह
आगे
चलेगा
ही
नही।
आपको
अगला
क्रम
पता
न
हो
तो
आप
दो-
चार
बार
प्रयास
करेंगे,
फिर
कहेंगे
मारो
गोली,
यह
नही
चल
रहा
है।
फिर
इसे
सीखने
का
उत्साह
समाप्त
हो
जाता
है
और
फिर
हम
उससे
कतराने
लगते
हैं।
तो
हमें
केवल
इतना
जानना
है
कि
जो
काम
हम
संगणकसे
करवाना
चाहते
हैं,
उस
काम
का
क्रम
कैसा
रहेगा।
वास्तव
में
यह
इतना
सरल
है
कि
पाच-
छह
बार
करने
पर
इसकी
समझ
भी
आ
जाती
है
और
आदत
भी
पड
जाती
है।
जिस
तरह
जादूगर
बडे
आराम
से
और
युक्तिसे
हर
एक
को
अपना
जादू
दिखाता
है,
उसी
तरह
संगणक
की
युक्तियाँ
हमारे
भी
समझने
में
आ
जाती
है।
तो
सीखनी
है
केवल
कई
छोटी
छोटी
युक्तियाँ
।
और
हां,
यदि
कोई
दोस्त
थोडी
देर
साथ
आये,
रहे,
और
ये
युक्तियाँ
सिखा
दे
तो
यह
और
भी
सरल
बात
हो
जाती
है।
लेकिन
तब
हमारा
भी
कर्तव्य
बन
जाता
हैकि
हम
भी
किसी
और
को
ऐसे
ही
दोस्ती
निभाकर
कर
संगणक
सिखायें।
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