It is also safer as the regular refrigerators cause damage to the ozone layer by releasing harmful gases.
However, one limitation is that with the current technology, the efficiency of such refrigerators is rather low.
Showing posts with label Electromagnetism. Show all posts
Showing posts with label Electromagnetism. Show all posts
Friday, January 06, 2006
A Better Refrigerator
Using the phenomena known as Peltier's Effect, it can be inferred that if there be a junction of two condunctors joined together, then it absorbs heat on passing current through it. Therefore, it can cool its surrounding region. Thus, it can be used in a refrigerator. There is no noise as no motors are run.
It is also safer as the regular refrigerators cause damage to the ozone layer by releasing harmful gases.
However, one limitation is that with the current technology, the efficiency of such refrigerators is rather low.
It is also safer as the regular refrigerators cause damage to the ozone layer by releasing harmful gases.
However, one limitation is that with the current technology, the efficiency of such refrigerators is rather low.
Thursday, January 05, 2006
Principles of Electricity and Magnetism
The laws of electromagnetism can be summarised in four famous equations known as Maxwell Equations after the famous physicist James Clark Maxwell.
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History of Electricity and Magnetism
The history of development of physics of electricity and magnetism is very old and interesting.
In 600 B.C., the Greek philosopher, mathematician and astronomer, Thales of Miletus (636-546 B.C.) observed that amber, when rubbed with silk aquires special properties - produces sparks and attracts small pieces of straw. The commonly used words electricity, electron etc. come from the greek name for amber, elektron. Thales also observed that pieces of magnetic rock called loadstone also have such powers. The words magnet and magnetism etc. come from the name of the place called Magnesia where loadstone was found.
The study of Electric and Magnetic phenomena remained almost univestigated for a long time after this.
William Gilbert (1540-1603) of England carried out systematic experiments related to electricity and magnetisms and described them in his famous book, De Magnete. He recognized that earth was a huge magnet. The invention of the electroscope is credited to him. Electroscope is an instrument useful for observing electrostatic effects.
The American Scientist Benjamin Franklin(1706-1790), famous for his kite-experiment, established the law of conservation of charge and discovered that there are two kinds of charge. He also invented the lightning rod.
Charles Augustin de Coulomb (1736-1806) performed measurements of electric and magnetic forces with a delicate torsion balance he had himself invented. He came up with the famous Coulomb's Law which gives the magnitude of force between two point charges.
F = kq1q2/r2
where,
F is the Force
q1and q2 are the values of the two point charges,
r is the separation between them.
k is a constant of proportionality
The unit of charge Coulomb(C) is named in his honour.
The production of electric currents was achieved by Alessandro Volta (1745-1827) of Italy around the year 1800. He invented the voltaic cell and the electric battery by connecting the cells in series. The unit of potential (Volt, V) is named in his honour.
The famous Gauss theorem in vector calculus (also known as the Divergence theorem) was formulated by the gifted German mathematician Karl Friedrich Gauss (1777-1855) around this time. The unit of Magnetic Field Strength (gauss, G) is named in his honour.
A vital event in the history of electricity and magnetism took place in 1819. Hans Christian Oersted (1777-1851), a Danish Professor of Physics discovered that a curent carrying wire caused a nearby compass needle to deflect. This was the first time when a link was found between electric and magnetic phenomena. Before this, electricity and magnetism were studied as independent phenomena.
In 1820, the French Physicist Andre Marie Ampere (1775-1836) invented the solenoidal coil. Solenoidal coils can produce magnetic fields. Ampere proposed that atoms are magnetized by tiny electric currents circulating in them. The unit of electric current (ampere, A) is named in his honour.
Georg Simon Ohm (1787-1854)of Germany gave his famous law known as the Ohm's law relating the voltage, current and resistance of a conductor. The unit of resistance (ohm) is named in his honour.
Under identical external conditions, for a conductor
V = RI
where,
V is the potential difference across the ends of the conductor
I is the electric current flowing in the conductor
R is the resistance of the conductor
This law of Ohm was not readily accepted initially.
That electricity could produce magnetic effects was demonstrated by Oersted as seen above, when an electric current caused deflection of a compass needle. The reverse phenomena, i.e., the production on electricity through magnetism was discovered by Michael Faraday (1791-1867) of London in 1831. Faraday observed that a changing magnetic field could produce an electric current. The unit of capacitance (Farad, F) is named in his honour. Also, the amount of charge on one mole of electrons, i.e. 96,000 coulomb is given the name Faraday.
The above effect, that is production of electricity by a changing magnetic field was observed independently by Joseph Henry of New York. The Electric Telegraph and Relay were invented by Henry. The unit of Inductance (Henry, H) is named in his honour.
A unification of the many laws of electricity that had been discovered was to come with the physicist James Clerk Maxwell (1831-1879), a professor at Cambridge University, England. He published a unified theory of electromagnetism in 1873. His equations show in an elegant manner the interdependence of electricity and magnetism. He postulated that light is an electromagntic wave and electromagnetic waves exist for other wvaelength than known for light. However, his work did not receive immediate acceptance. Physicists of the time were skeptical of his theories.
It was Heinrich Hertz (1857-1894) in 1888 who demonstrated the existence of electromagnetic waves. Hertz was a professor of physics at Karlsruche, Germany. He generated and detected radio waves and showed that their behavior was similar to that of light.
A sensation was created by Guglielmo Marconi (1874-1931) in 1901 by sending radio signals across the atlantic ocean. He applied the laboratory experiments of Hertz to practical appliations. Marconi developed radio communication for ships. With this, ships, when at the sea, were no longer in complete isolation. Now they could be in contact with people on land. The radio, thus, became very popular and important.
The American inventor Thomas Alva Edison (1847-1931) put electricity and magnetism to extensive use. He made several inventions in the fields of telegraphy, lighting and power generation. He is popularly known as the inventor of the light bulb.
Nikola Tesla (1856-1943) developed the induction motor. He was an advocator of the use of alternating current for transmission and distribution of electricity. He designed the power generating system at Niagra falls.The unit of Magnetic Field (Tesla, T) in named in his honour.
In 1905, the great physicist Albert Einstein (1879-1955) theorized his famous theory of relativity. The theory tells us that the manifestation of the electric field or magnetic field depends upon the motion of the observer.
In 600 B.C., the Greek philosopher, mathematician and astronomer, Thales of Miletus (636-546 B.C.) observed that amber, when rubbed with silk aquires special properties - produces sparks and attracts small pieces of straw. The commonly used words electricity, electron etc. come from the greek name for amber, elektron. Thales also observed that pieces of magnetic rock called loadstone also have such powers. The words magnet and magnetism etc. come from the name of the place called Magnesia where loadstone was found.
The study of Electric and Magnetic phenomena remained almost univestigated for a long time after this.
William Gilbert (1540-1603) of England carried out systematic experiments related to electricity and magnetisms and described them in his famous book, De Magnete. He recognized that earth was a huge magnet. The invention of the electroscope is credited to him. Electroscope is an instrument useful for observing electrostatic effects.
The American Scientist Benjamin Franklin(1706-1790), famous for his kite-experiment, established the law of conservation of charge and discovered that there are two kinds of charge. He also invented the lightning rod.
Charles Augustin de Coulomb (1736-1806) performed measurements of electric and magnetic forces with a delicate torsion balance he had himself invented. He came up with the famous Coulomb's Law which gives the magnitude of force between two point charges.
F is the Force
q1and q2 are the values of the two point charges,
r is the separation between them.
k is a constant of proportionality
The unit of charge Coulomb(C) is named in his honour.
The production of electric currents was achieved by Alessandro Volta (1745-1827) of Italy around the year 1800. He invented the voltaic cell and the electric battery by connecting the cells in series. The unit of potential (Volt, V) is named in his honour.
The famous Gauss theorem in vector calculus (also known as the Divergence theorem) was formulated by the gifted German mathematician Karl Friedrich Gauss (1777-1855) around this time. The unit of Magnetic Field Strength (gauss, G) is named in his honour.
A vital event in the history of electricity and magnetism took place in 1819. Hans Christian Oersted (1777-1851), a Danish Professor of Physics discovered that a curent carrying wire caused a nearby compass needle to deflect. This was the first time when a link was found between electric and magnetic phenomena. Before this, electricity and magnetism were studied as independent phenomena.
In 1820, the French Physicist Andre Marie Ampere (1775-1836) invented the solenoidal coil. Solenoidal coils can produce magnetic fields. Ampere proposed that atoms are magnetized by tiny electric currents circulating in them. The unit of electric current (ampere, A) is named in his honour.
Georg Simon Ohm (1787-1854)of Germany gave his famous law known as the Ohm's law relating the voltage, current and resistance of a conductor. The unit of resistance (ohm) is named in his honour.
Under identical external conditions, for a conductor
where,
V is the potential difference across the ends of the conductor
I is the electric current flowing in the conductor
R is the resistance of the conductor
This law of Ohm was not readily accepted initially.
That electricity could produce magnetic effects was demonstrated by Oersted as seen above, when an electric current caused deflection of a compass needle. The reverse phenomena, i.e., the production on electricity through magnetism was discovered by Michael Faraday (1791-1867) of London in 1831. Faraday observed that a changing magnetic field could produce an electric current. The unit of capacitance (Farad, F) is named in his honour. Also, the amount of charge on one mole of electrons, i.e. 96,000 coulomb is given the name Faraday.
The above effect, that is production of electricity by a changing magnetic field was observed independently by Joseph Henry of New York. The Electric Telegraph and Relay were invented by Henry. The unit of Inductance (Henry, H) is named in his honour.
A unification of the many laws of electricity that had been discovered was to come with the physicist James Clerk Maxwell (1831-1879), a professor at Cambridge University, England. He published a unified theory of electromagnetism in 1873. His equations show in an elegant manner the interdependence of electricity and magnetism. He postulated that light is an electromagntic wave and electromagnetic waves exist for other wvaelength than known for light. However, his work did not receive immediate acceptance. Physicists of the time were skeptical of his theories.
It was Heinrich Hertz (1857-1894) in 1888 who demonstrated the existence of electromagnetic waves. Hertz was a professor of physics at Karlsruche, Germany. He generated and detected radio waves and showed that their behavior was similar to that of light.
A sensation was created by Guglielmo Marconi (1874-1931) in 1901 by sending radio signals across the atlantic ocean. He applied the laboratory experiments of Hertz to practical appliations. Marconi developed radio communication for ships. With this, ships, when at the sea, were no longer in complete isolation. Now they could be in contact with people on land. The radio, thus, became very popular and important.
The American inventor Thomas Alva Edison (1847-1931) put electricity and magnetism to extensive use. He made several inventions in the fields of telegraphy, lighting and power generation. He is popularly known as the inventor of the light bulb.
Nikola Tesla (1856-1943) developed the induction motor. He was an advocator of the use of alternating current for transmission and distribution of electricity. He designed the power generating system at Niagra falls.The unit of Magnetic Field (Tesla, T) in named in his honour.
In 1905, the great physicist Albert Einstein (1879-1955) theorized his famous theory of relativity. The theory tells us that the manifestation of the electric field or magnetic field depends upon the motion of the observer.
Related Links:
Applications of Electricity and Magnetism
Electric and Magnetic phenomena find applications in many fields of physics and technology. The discovery of electromagnetic induction and the subsequent invention of electic generator and the motor had revolutionised the development of technology.
Today the nature of Electric and Magnetic Fields has been well understood and various advanced devices are used that put them into use. Electromagnetic phenomena are used in therapy also. Infrared therapy and magnetic therapy are widely used.
Explore and read around some applications of electromagnetism -
Cherenkov Free Electron Laser - The CFEL uses a relativistic electron beam and generates a high power coherent radiation, acting as a laser. An interesting application of electromagnetism.
Noiseless, motorless and safer refrigerator - Using the Peltier effect (a thermoelectric effect), one can make a refrigerator that works without noise, or any running motors. It is also a safer method of refrigeration as it does not release harmful gases into the atmosphere.
Earth's Behavior as a Magnet - Earth is well known to behave as a magnet. Loadstones were used in olden times to use this magnetism in navigation. Learn about the changing patterns in the magnetic field.
Electric Field in Conductors - Read about the interesting behavior of conductors in an electric field, the shielding effect in cavities, and why is it safe to sit inside the high voltage terminal of a million-volt van de graff generator.
Today the nature of Electric and Magnetic Fields has been well understood and various advanced devices are used that put them into use. Electromagnetic phenomena are used in therapy also. Infrared therapy and magnetic therapy are widely used.
Explore and read around some applications of electromagnetism -
Cherenkov Free Electron Laser - The CFEL uses a relativistic electron beam and generates a high power coherent radiation, acting as a laser. An interesting application of electromagnetism.
Noiseless, motorless and safer refrigerator - Using the Peltier effect (a thermoelectric effect), one can make a refrigerator that works without noise, or any running motors. It is also a safer method of refrigeration as it does not release harmful gases into the atmosphere.
Earth's Behavior as a Magnet - Earth is well known to behave as a magnet. Loadstones were used in olden times to use this magnetism in navigation. Learn about the changing patterns in the magnetic field.
Electric Field in Conductors - Read about the interesting behavior of conductors in an electric field, the shielding effect in cavities, and why is it safe to sit inside the high voltage terminal of a million-volt van de graff generator.
Related Links:
Introduction to Electricity and Magnetism
Electric and magnetic phenomena arise out of a fundamental property of matter known as charge. The two types of charges existing in nature and their interactions give rise to a number of interesting and useful phenomena. It is these interactions that provide strength to matter around us. The flow of charge provides us with the all useful electricity. These in form of magnetism are responsible for the working a large number of devices that include floppy disks, casettes etc.
Earth's magnetism is responsible for the working of the magnetic compass.
Waves used for transmission of information and data, and light itself are formed out of oscillating electric and magnetic fields - arising from oscillating charges.
Most of the appliances and equipments that we use in our daily life like the computer, industrial machinery and home appliances are applications of principles of electricity and magnetism.
The various electric and magnetic phenomena are analyzed with the help of principles of potential and fields. A charged particle interacts with another charged particle by setting up electric and magnetic fields in space which in turn influence the other particle. These electric and magnetic fields themselves have rather interesting properties and as mentioned above, their oscillations turn up in the form of light and other electromagnetic waves.
Waves used for transmission of information and data, and light itself are formed out of oscillating electric and magnetic fields - arising from oscillating charges.
Most of the appliances and equipments that we use in our daily life like the computer, industrial machinery and home appliances are applications of principles of electricity and magnetism.
The various electric and magnetic phenomena are analyzed with the help of principles of potential and fields. A charged particle interacts with another charged particle by setting up electric and magnetic fields in space which in turn influence the other particle. These electric and magnetic fields themselves have rather interesting properties and as mentioned above, their oscillations turn up in the form of light and other electromagnetic waves.
Cherenkov Free Electron Laser
Introduction:
Cherenkov Free electron laser (CFEL) generates coherent high power radiation. The laser uses a relativistic electron beam as the lasing medium, and hence it is called a "free electron laser".Components and functioning of the CFEL
Design of the Cherenkov Free Electron Laser
The CFEL consists of an electron gun which uses high voltage to accelerate the electrons to relativistic speeds. The beam passes through a cylindrical waveguide which is filled with a dielectric near its boundary and has vacuum near the axis. This is done to make the velocity of electromagnetic waves inside the waveguide less than c, the speed in vacuum. At this decreased speed of the electromagnetic wave, the electron beam can interact with it. This interaction causes the electromagnetic wave to grow in amplitude and is responsible for the lasing action. The mechanism for this process is described later.Inside the waveguide, a strong magnetic field is produced by wounding solenoids outside the cylindrical waveguide and passing high current though them. This magnetic field does not let the electron beam diverge radially. This is required to keep the electron beam traveling in the axial direction so that it can interact with the electromagnetic wave, which has the electric field in the axial direction. Note that the wave is also traveling in the axial direction. Such electromagnetic waves, which have the electric field in the same direction as the direction of propagation are said to be propagating in a Transverse Magnetic mode, or a TM mode.
A necessary condition for the functioning of the Cherenkov Free Electron Laser is that the phase velocity of the electromagnetic wave should be nearly equal to the velocity of the electron beam in magnitude. This makes the frequency of the electromagnetic wave, as seen by the electrons, nearly zero (Doppler Shift in frequency). Hence the electric field of the wave appears like an electrostatic field to the electrons, and hence can continuously accelerate or decelerate electrons.
Growth of the Wave
For our purpose, we need to decelerate the electrons, so that the energy is transferred to the Electromagnetic wave, so that it grows. In a case where the phase velocity of the wave is exactly equal to the electron beam velocity, half of the electrons see the electric field in the direction of their motion, and half see it opposite to it. However, for a net retardation of the electrons, there should be more number of electrons in the retarding zones. This is achieved by keeping the electron beam velocity slightly higher than the phase velocity of the wave.In this condition, the electrons in the accelerating zones are accelerated over to the decelerating zones while the electrons in the decelerating zones are slowed down and remain in the decelerating zones. In this way, the number of electrons in the retarding zones is increased. This leads to a net retardation of the electrons and in turn to the growth of the wave.
After emerging out of the waveguide, the electron beam is sent to a beam dump.
Cherenkov free electron laser is sometime mentioned as Cerenkov Free electron laser.
Electric Field in Conductors
"It is safe to sit inside the high voltage terminal of a million-volt van de graff generator, without worrying about getting a shock".
- Richard Feynman, The Feynman Lectures on Physics, Vol 2.
The above statement by Feynman shows the interesting beavior of conductors in an electric field. The van de graff generator has a metallic sphere at a very high potential, but the field inside it is zero, so that there is not potential difference between any two points inside the sphere, and hence one would experience no electric shock inside it. This is an example of shielding of electric field by conductors.
These surface charges would produce an electric field of their own from the right to the left, in a direction opposite to the applied electric field. This transfer of electrons would go on until the field due to these surface charges exactly cancels the applied electric field inside the conductor, since after that, charges inside the conductor do not feel any force.
Thus, because of the presence of free to move charges, the electric field has been cancelled inside the metal. Note again that this true only in case of a static electric field, i.e. electric field that is not changing with time.
- Richard Feynman, The Feynman Lectures on Physics, Vol 2.
The above statement by Feynman shows the interesting beavior of conductors in an electric field. The van de graff generator has a metallic sphere at a very high potential, but the field inside it is zero, so that there is not potential difference between any two points inside the sphere, and hence one would experience no electric shock inside it. This is an example of shielding of electric field by conductors.
Conductor in a static electric field.
Let us first see a basic example of the way conductors behave in an electric field. Assume that there is a metallic conducting block placed in a static electric field (that is, the field is not changing with time). There are a lot of free electrons inside a conductor, which are randomly distributed throughout the bulk of the conductor in the case of no applied electric field. Now when the electric field is applied, the electrons feel a force in the direction opposite to the direction of the field, since they are negatively charged, and hence move to the left surface of the conductor as shown in the figure. This aggregating of electrons to the left surface causes a net positive charge on the right surface.
These surface charges would produce an electric field of their own from the right to the left, in a direction opposite to the applied electric field. This transfer of electrons would go on until the field due to these surface charges exactly cancels the applied electric field inside the conductor, since after that, charges inside the conductor do not feel any force.
Thus, because of the presence of free to move charges, the electric field has been cancelled inside the metal. Note again that this true only in case of a static electric field, i.e. electric field that is not changing with time.
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The Electric Potential
We can calculate the electric field in various circumstances using the familiar Coulomb's law or the Gauss' law. Although these laws are universally applicable, calculating the Electric field for a particular situation might not be easy using these laws. So we have another useful method to calculate the field and related quantities.
In our new method, we note that the line integral of electric field around a closed loop is zero (remember, this is true only in a static condition, that is, when the charges aren't moving), or equivalently, the curl of E is zero. Now, it is a theorem from vector calculus that if the curl of a quantity is zero, then that quantity is definitely the gradient of some scalar quantity.
If you aren't familiar with this theorem, or want some better physical picture, here's the argument. The work done by the electrostatic field on an object doesn't depend on the path that the object takes in the region of the field, It depends only on the starting position and on where the object ultimately lands up, the direction and magnitude of the electric field, and the magnitude of the charge.
Say the charge on the object is 1 nC and say the object is displaced 5 metres in a direction parallel to the field (even if the object moves at angle, we can resolve the displacement components and need to consider only the component parallel to the field). The work done on it is independent of the path it takes, we just need to ensure that it has the same displacement via each path. Say we find that work done on the object by the field is 1mJ (We can find it out by measuring the change in its Kinetic Energy which is also 1mJ if no other force is doing work on the object).
Now we take another charge, this time 5nC, and find out the work done on it (for the same displacement, of course), we find that the work done is 5mJ. The work has become 5 times. (It will actually turn out to be so.) This independence of path shows that we can define a scalar quantity at every point in space, independent of any charge, and if you carry a charge from one point to another, you can calculate the work done on it just by knowing the values of that scalar quantity at the two points (and the value of the charge!). This scalar is called the electrostatic potential.
The new method that I referred to, for calculating the field in a circumstance, is finding out the potential first, (since being a scalar, its easy to find out) and then from the potential, finding out the electric field.
Principles of Electricity and Magnetism
Introduction to Electricity and Magnetism
In our new method, we note that the line integral of electric field around a closed loop is zero (remember, this is true only in a static condition, that is, when the charges aren't moving), or equivalently, the curl of E is zero. Now, it is a theorem from vector calculus that if the curl of a quantity is zero, then that quantity is definitely the gradient of some scalar quantity.
If you aren't familiar with this theorem, or want some better physical picture, here's the argument. The work done by the electrostatic field on an object doesn't depend on the path that the object takes in the region of the field, It depends only on the starting position and on where the object ultimately lands up, the direction and magnitude of the electric field, and the magnitude of the charge.
Say the charge on the object is 1 nC and say the object is displaced 5 metres in a direction parallel to the field (even if the object moves at angle, we can resolve the displacement components and need to consider only the component parallel to the field). The work done on it is independent of the path it takes, we just need to ensure that it has the same displacement via each path. Say we find that work done on the object by the field is 1mJ (We can find it out by measuring the change in its Kinetic Energy which is also 1mJ if no other force is doing work on the object).
Now we take another charge, this time 5nC, and find out the work done on it (for the same displacement, of course), we find that the work done is 5mJ. The work has become 5 times. (It will actually turn out to be so.) This independence of path shows that we can define a scalar quantity at every point in space, independent of any charge, and if you carry a charge from one point to another, you can calculate the work done on it just by knowing the values of that scalar quantity at the two points (and the value of the charge!). This scalar is called the electrostatic potential.
The new method that I referred to, for calculating the field in a circumstance, is finding out the potential first, (since being a scalar, its easy to find out) and then from the potential, finding out the electric field.
Principles of Electricity and Magnetism
Introduction to Electricity and Magnetism
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