Electricity and Magnetism - . The forces on the left and right wires produce no torque since the moment arm is zero for each (they point right at the center). For an electron we would say its spin magnetic dipole moment vector, Vs, points up. In this article, we discussed the magnetic properties of solids. Your email address will not be published. 7. Chemically substances having same type of formulae are not necessarily Isomorphous. To do this you would, of course, align A with the light rays. essential concepts and summary. The The contribution of the orbital magnetic moment is equal to mi mB, where mi is the magnetic quantum number of the electron. For each electron in an atom, the spin magnetic moment is mB (depending upon the two possibilities of the spin). Superconductivity:A substance is said to be superconducting when it offers no resistance to the flow of electricity. ISSUES TO ADDRESS. (Fig. magnetic fields. There are How does magnetic memory storage work?. If a charge is motionless relative to the field, there is no magnetic force on it, but if either a magnet is moving or a charge is moving, there could a force on the charge. In 1830 Michael Faraday (British) and Joseph Henry (American) independently discovered that a changing magnetic field produced a current in a coil of wire.
Ralls, T.H. i, j, and k are the unit vectors pointing, along the positive x, y, and z axes, respectively. Motion of a Charge in a Magnetic Field The x 's represent field lines pointing into the page. - Chapter 8 Nuclear Magnetic Resonance Spectroscopy http://www.yteach.co.uk/page.php/resources/view_all?id=nuclear_magnetic_resonance_NMR_spectroscopy_spin_spectrometer - What kind of information do you and your friend need to figure out the dog s breed? 2. This is the basic idea behind an electric motor. How do we explain magnetic phenomena?. A graph of the current output from an AC generator produces a sinusoidal curve due to the periodic nature of the generator's rotation. Ferrimagnetism is observed when the magnetic moments of the domains in the substance are aligned in parallel and anti-parallel directions in unequal numbers. (v) Anti-ferromagnetic substances:Substances which are expected to posses paramagnetic behaviour, ferromagnetism on the basis of unpaired electron but actually they possess zero not magnetic moment are called anti-ferromagnetic substances.Example: MnO2. This is known as Curie Temperature. +/- mag. 20.20(a), Callister 6e. 20.6, Callister 6e. They are weakly attracted by the magnetic fields. s. Materials and Magnetism ' Each electron in an atom has two magnetic dipole moments associated with it, one for spin, and one for orbit. A materials magnetic reaction is largely determined by the magnetic dipole moment associated with the electrons intrinsic angular momentum, or spin. The other type of magnetic moment originates from electron spin which is directed along the spin axis. their spins are not neutralized. Thus dipoles are formed. 9, SUMMARY A magnetic field can be produced by: --putting a current through a coil. moving charges, Magnetism Notes I. How are magnetic material | PowerPoint PPT presentation | free to view, Chapter 8 Periodic Properties of the Elements, - Chemistry: A Molecular Approach, 1st Ed. Induced emf's and Currents The current induced in a loop come not from a battery but from a changing magnetic flux. 20.4, Callister 6e. It is equal to 9.27 1024A m2. They also exclude magnetic field lines (the Meissner effect) which makes magnetic levitation possible. 22.1. magnetism. strong magnetic properties. The paramagnetic impacts are boosted by more unpaired electrons. Substances like MnO showing antiferromagnetism have domain structure similar to ferromagnetic substance, but their domains are oppositely oriented and cancel out each others magnetic moment. E itself depends on the rate at which the flux inside the loop is changing.
In addition to these dipoles, there may also be permanent dipoles in the crystal. When the magnet is withdrawn the flux decreases and current is induced in the other direction. LearnPick does not verify the identity or authenticity of information posted by tutors or students. In the 1600's William Gilbert, physician of Queen Elizabeth I, concluded that Earth itself is a giant magnet. 6, FERRO- & FERRI-MAGNETIC MATERIALS As the applied field (H) increases --the magnetic moment aligns with H. Adapted from Fig. This process converts mechanical energy into electrical energy, The simplest form of an electric generator is called an alternating current (AC) generator. NUCLEAR MAGNETIC RESONANCE - . just, Chapter 28 Magnetic Fields - . Their tendency to form magnets is an interesting feature of transition metals. For more information download BYJUS The Learning App. At high temps these domains can align in the presence of an external field (like Earth's) leaving a permanent magnet. If a charge moves parallel to a magnetic field, there is no magnetic force on it, since sm 0.
what are the, Chapter 21 Summary: Magnetic Forces and Magnetic Fields - . The magnetic field vector is always tangent to the magnetic field. Suppose the magnetic field strength inside is 0.07 T and a 4.3 mc charge is moving through the field at right angle to the field lines. Magnetism refers to the properties and interactions of magnets A. And, again, its all free. Lets melt the iron, and bring in a magnetic field. Our new CrystalGraphics Chart and Diagram Slides for PowerPoint is a collection of over 1000 impressively designed data-driven chart and editable diagram s guaranteed to impress any audience. Every electron in an atom behaves as a magnet in two ways, each having two magnetic dipole moments: Spin magnetic dipole moment - due to the "rotation" of an electron.
This is one source of magnetism. Guoys Method of Studying Magnetic Properties of Solids: The method consists of weighing the substances in an out of the magnetic field. (Fig. Materials design for magnetic storage. As the loop turns it eventually reaches a vertical position (the plane of the loop parallel to the field). The document Magnetic Properties of Solids Notes | Study Chemistry for JEE - JEE is a part of the, Full syllabus notes, lecture & questions for Magnetic Properties of Solids Notes | Study Chemistry for JEE - JEE - JEE | Plus excerises question with solution to help you revise complete syllabus for Chemistry for JEE | Best notes, free PDF download. Diamagnetism is 
- Chapter 2 Atoms, Molecules, AP Chemistry 2008-2009 Mrs the produce CO or CO and not something like CO1.6 2.2 The Discovery of Atomic Structure The atom is - Chapter 19 Nuclear Magnetic Resonance Dr. Nizam M. El-Ashgar Chemistry Department Islamic University of Gaza * * Chapter19 * Chapter19 * Therefore, the absorption - Sonar Satellites Deep-sea corers Magnetic recorders Robotic vehicles Properties of Water Density Thermocline Deep water Most energy - Chemistry, The Central Science the size of the atom itself! For each approved PPT you will get 25 Credit Points and 25 Activity Score which will increase your profile visibility. Consists of unpaired electrons, all having the same direction, Dipole moments are arranged in a compensatory way, Unequal number of parallel and antiparallel arrangement of magnetic moments. The greater the current and the more turns per unit length, the greater the field inside. Contains at least one unpaired electron in the orbital. 10. introduction. The resultant vectors from each electron then combine for the whole atom, often canceling each other out. ' Magnetic Flux Magnetic flux, informally speaking, is a measure of the amount of magnetic field lines going through an area. Note: with the window oriented parallel to the rays, 900 and = 0 (no light enters the window). Nivaldo Tro Chapter 8 Periodic Properties of the Elements Roy Kennedy Massachusetts Bay Community College. They are magnetized in a magnetic field in the same direction. B decreases as x increases. Diamagnetic substances are weakly repelled by a magnetic field. Electrons can also be referred to as small loops of current which retain their magnetic moment. We can think of the loop containing an imaginary battery that gets turned on whenever flux in the loop changes. Note how the E field due an electric dipole is just like the magnetic field (B field) of a bar magnet. Wrap your right hand along the loop in the direction of the current and your thumb points in the direction of the north pole of your electro- magnet. When we try to separate the two poles by breaking the magnet, we only succeed in producing two distinct dipoles (pic on right). Charge in motion once again produces a magnetic field. How strong and which way is the magnetic force on the S charge? Prodding Magnetic Properties Of Electrodeposited Nickel By Magnetic Force Microscope (MFM) - . For some materials each atom has a nonzero dipole moment, but because the atoms have all different orientations, the material as a whole remains nonmagnetic. ' To oppose this change in flux a current is induced in the direction S Java script shown. (hard drive) Adapted from Fig. One simple example of this is a magnet moving in and out of a wire loop. Sources of Magnetism We have seen charges in motion (as in a current) produce magnetic fields. electrons behave like tiny magnets. In a generator we'll see that a torque on a current loop inside a magnetic field produces a current. - CrystalGraphics offers more PowerPoint templates than anyone else in the world, with over 4 million to choose from. 74 (7), p. 4646, 1993. ) 
Chapter 18: Magnetic Properties. For most materials the net dipole moment for each atom is about zero. ' properties of magnets magnetic poles polarized -, Magnetism - . As the turbines rotate, current loops turn through a magnetic field to generate electricity. Thus introduction. He discovered that a magnet had two magnetic poles North and South poles. 
Put your understanding of this concept to test by answering a few MCQs. CHAPTER 20:MAGNETIC PROPERTIES ISSUES TO ADDRESS How do we measure magnetic properties? - Chapter 7: Energy and Chemical Change Chemistry: The Molecular Nature of Matter, 6E Jespersen/Brady/Hyslop 1. 20.16 from K.M. All the electrons in the orbitals are paired and are completely filled. The magnitude of this magnetic moment is very small and is measured in the unit called Bohr magneton B. Its electronic configuration is [Ar] 3d6 4s2. Bar magnet demo. Since it consists of many current loops, the resemblance to a bar magnet's field is much better than that of a single current loop. Get powerful tools for managing your contents. Head can --apply magnetic field H & align domains (i.e., magnetize the medium). Magnetic induction: --occurs when a material is subjected to a magnetic field. At point P inside the solenoid, the B field is a vector sum of the fields due to each section of wire. Also, the south pole of this magnet is near the geographic north pole, NG.
12H2O and Na3ASO4. The net force on the loop is zero, but the net torque about the center is nonzero. properties of magnets magnetic properties of materials the magnetic field of the earth. You might even have a presentation youd like to share with others. Physical properties (e.g.- mass, volume - Electricity and Magnetism Chapter 7 Section 1 Chapter 8 Sections 2 & 3, Chapter 1 Structure Determines Properties, - Title: Carey Chapter 1 Chemical Bonding Author: Monte Wolf Last modified by: mwolf Created Date: 3/30/2000 4:09:52 PM Document presentation format, CHAPTER 1* Introduction: Matter and Measurement. Adapted from Fig. Magnetic Field of a Current Carrying Wire 1. digital information is stored on a hard disk as microscopic patches of magnetism. The induced current is always in a direction that opposes the change in flux. Examples: H2O, TiO2, V2O5, NaCl and C6H6. 8. MAGNETIC PROPERTIES OF NICKEL DOPED TITANIUM DIOXIDE: .Magnetic properties of nickel doped titanium, Explain Magnetic and Dielectric Materials properties K2 2.1. 20.18, Callister 6e. Fig. Since v is L to B, F = FB = q VB. They'll give your presentations a professional, memorable appearance - the kind of sophisticated look that today's audiences expect. This happens at the Mid-Atlantic Ridge beneath the Atlantic Ocean. Faraday, who was perhaps the greatest experimentalist of all time, came up with the idea of electric and magnetic "fields." And, best of all, it is completely free and easy to use. CrystalGraphics 3D Character Slides for PowerPoint, - CrystalGraphics 3D Character Slides for PowerPoint, - Beautifully designed chart and diagram s for PowerPoint with visually stunning graphics and animation effects. The field is static but as the loop turns as the number of field lines poking through it changes. The mag. The magnitude of orbital motion is equal to mlBand is directed along the axis of rotation.
--detect a change in the magnetization of the medium. Just prior to this, as the loop was approaching horizontal, the number of field lines inside it was increasing, so the current was in the other direction to oppose this change. 20.5(b), Callister 6e. Out B is uniform here but only in the region shown.
The power of the magnets depends on the object that comes into contact with the magnet. To know about the electrical properties and dielectric properties of solids. This is the equilibrium point. The electricity thus produced is called piezoelectricity and the crystals are called piezoelectric crystals. Magnetic Fields: Overview Current in wire 4. moment along axis. magnetic fields magnetic force on a point charge motion of a charged particle, CHAPTER 19: MAGNETISM - . - CHAPTER 1* Introduction: Matter and Measurement Suh Kwon 1.1 The Study of Chemistry The Molecular Perspective of Chemistry Matter = physical material of the - Electricity and Magnetism Electricity and Magnetism Properties of Magnets Magnetic Properties of Materials The Magnetic Field of the Earth. Also note that there is no battery in the loop! phy1013s. If you have your own PowerPoint Presentations which you think can benefit others, please upload on LearnPick. Since F is a centripetal force, F = FC = m v2/ R. Let's see how speed, mass, charge, x x x x x x x x x x x x x x x x X x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x field strength, and radius of x curvature are related: x x x x x. - Nuclear Magnetic Resonance Dr NMR detection is being coupled with liquid chromatographic separation in HPLC-NMR instruments for identification of components of Chapter 2 Hardware Designed to Meet the Need. (iii) Ferromagnetic substances:Substances which show permanent magnetism even in the absence of the magnetic field are called ferromagnetic substances.Example:, Fe, Ni, Co, CrO2. Lemke, MRS Bulletin, Vol. Quantum mechanics is required to explain fully the magnetic properties of electrons, but it is helpful to relate these properties back to the motion of charges. A compass points in the direction of the magnetic north pole, NM, around which the field lines reenter Earth's surface. Earth's Magnetic Field 11.50 S Vorb Earth's field looks similar to what we'd expect if there were a giant bar magnet imbedded inside it, but the dipole axis of this magnet is offset from the axis of rotation by 11.50. How do we measure magnetic properties ?. A + charge at P is moving out of the page. A typical example of such crystals is Lead zirconate (PbZrO3). Each is a vector. ' no unpaired electrons. Magnetic force is the in, PHY1013S MAGNETIC FIELDS - . - Chemistry I Electrons in Atoms Chapter 5 46.) Sometimes it may be convenient to use the gauss, which is equal to 1/10,000 of a tesla. The current changes direction twice with each turn--whenever the loop is horizontal. In the 1900's scientists discover superconductivity. This relationship is known as Curies law. Graphs showing the effect of temperature on magnetization of materials. a, What Produces Magnetic Field? you can investigate the properties of magnets by bringing two magnets, Chapter 26 Properties of Light - Part vi: light. Note: Electrons are not actually little balls that rotate and revolve like planets, but imagining them this way is useful when explaining magnetism without quantum mechanics. Materials design for magnetic storage. Electric Motor d Current along with a magnetic field can produce torque. But since its charge is negative, the spinning ball is like a little current loop flowing in the direction opposite its rotation, and the ball becomes an electromagnet with the N pole up. This would amount to simple harmonic motion of the loop, which is not particularly useful. The Magnetic Field - . These crystals are used as pick-ups in record players where they produce electrical signals by application of pressure. properties of magnets. A + charge at Q is moving up. They are weakly attracted by a magnetic field as compared to ferromagnetic substances. In the United States, generator generally have a frequency of 60 Hz, which means the current switches direction 120 times every second! History of Magnetism The first known magnets were naturally occurring lodestones, a type of iron ore called magnetite (Fe304). 2. magnetic, Chapter 24: Magnetic Fields - . field line there. however, when electric field is applied, polarization takes place because nuclei are attracted to one side and the electron cloud to the other side. Two media types: --Particulate: needle-shaped g-Fe2O3. The result here is AC, but (direct current) DC motors exist as well in which current only flows in one direction. The alignments of domains persist even when the magnetic field is removed and the ferromagnetic substance becomes a permanent magnet. (Fig. Examples:O2, Cu2+, Fe3+, Cr3+, TiO,Ti2O3, VO, VO2, and CuO. Physics, Mathematics, Chemistry, B.Sc Coaching, KV Students can find the best tutors and instructors through LearnPick's online tutoring marketplace. 4. Their three-dimensional magnetic field lines begin at the north end and loop around the south end. Note that the induced current produces its own magnetic field pointing to the right. These dipoles may align themselves in an ordered manner so that such crystals have a net dipole moment.Such polar crystals show the following interesting properties: (i) Piezoelectricity or Pressure - electricity:When mechanical stress is applied on such crystals so as to deform them, electricity is produced due to displacement of ions. electromagnetic waves. Yet another right hand rule helps with current loops: Wrap your right hand in the direction of the loop and your thumb points in the direction of B inside. Remember: moving charges produce magnetic fields, and external magnetic fields exert a magnetic force on moving charges (at least if the charge has a component of its velocity perpendicular to the field). Note B diminishes with distance from the wire. The situation is the same with a circular loop. Continued Electric Generator (cont.) These two dipole moments combine vectorially for each electron. ' Furthermore, all the atoms have the same alignment, at least within very tiny' regions called domains. field coming out of the page. A magnetic moment, with a magnitude and a direction, is a vector quantity. These torques work together to rotate the loop, converting electrical energy into mechanical energy. and an orbital magnetic moment associated with it. The strength of this battery is called the emf (electromotive force); it's symbol is a script E: E, and it's measured in volts. four unpaired electrons. An orbiting electron behaves like a tiny electromagnet with its N pole in the direction of Vorb. 20.7, Callister 6e. Thus F causes a centripetal acceleration. Besides strong attractions, these substances can be permanently magnetized. It also produces its own mag- netic field. Electric Generators In a motor we have seen that a current loop in an external magnetic field produces a torque on the loop. - PowerPoint PPT Presentation. - Chapter 5 Basic Properties of Light The chapter on Light is important for all studies in astronomy. key contents magnetic fields and the lorentz force the hall effect magnetic force on, Chapter 20: Magnetic Properties - . Track your progress, build streaks, highlight & save important lessons and more! In quantum mechanics, instead of circular orbits we speak of electrons behaving like waves and we can only talk of their positions in terms of probabilities. The first one is due to the orbital motion around the nucleus, and the second is due to the spin of electron around its own axis. 20.18 from J.U. Although a battery only pumps current in one direction, the change in direction of current can be accomplished with help of a commutator, as can be seen with these animations: Animation 1 Animation 2, Electromagnets: Straight Wire Permanent magnets aren't the only things that produce magnetic fields. People of ancient Greece and China discovered that a lodestone would always align itself in a longitudinal direction if it was allowed to rotate freely. - Magnetic Media Hard Disk Drives Magnetic Tape data and usage RAM CPU Registers cache ROM VRAM Hard Drive Tape Magnetic Storage CD DVD Optical Storage Chapter 4 Arrangement of Electrons in Atoms. 20.19, Callister 6e. A bar magnet is a simple example. magnetic fields magnetic circuits inductance and. In the ideal case the magnetic field would be uniform inside and zero outside. Outside the loop, say at P, the field is weak since the left side of the wire produces a field out of the page, but the right side produces a field into the page. The + charge in the pic in moving into the page. Examples: Fe3O4 (magnetite) and ferrites like MgFe2O4 and ZnFe2O4. Metal complexes that have electrons unpaired are magnetic. He also Invented the dynamo (a generator), made major contributions to chemistry, and invented one of the first electric motors ' In the 19th century James Clerk Maxwell, a Scottish physicist and one of the great theoreticians of all times, mathematically unified the electric and magnetic forces. It has millions of presentations already uploaded and available with 1,000s more being uploaded by its users every day. Courtney, and J. Wulff, Introduction to Materials Science and Engineering, John Wiley and Sons, Inc., 1976.) A moving electron may be considered to be a small current loop, generating a small magnetic field, and having a magnetic moment along its axis of rotation. Magnetic Dipoles Recall that an electric dipole consists of two equal but opposite charges separated by some distance, such as in a polar molecule. Spin Magnetic Dipole Moment Just as electrons have the intrinsic properties of mass and charge, they have an intrinsic property called spin. The - charge is moving to the right, so the q v vector is to the left. Thus, each domain acts as a tiny magnet. Adapted from Fig. A - charge at R feels a force into the page. Magnetic properties:The macroscopic magnetic properties of material are consequence of magnetic moments associated with the individual electron. A solenoid behaves as just like a simple bar magnet but only when current is flowing. magnetic material has the ability to exert forces on. Since fewer field lines are entering the loop, the induced current is in a direction to produce more field lines downward. It may be further pointed out here that each ferromagnetic substance has a characteristic temperature above which no ferromagnetism is observed. Adapted from Fig.
XV, No. Different types of materials show different properties in the presence of a magnetic field. Kim, S. Guruswamy, and K.E. This is reminiscent of angular momentum for a spinning body. Unlike E fields, all magnetic field lines that come from the N pole must land on the S pole--no field lines go to or come from infinity. B out of page B into page x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x, Current Loops and Magnetic Fields The magnetic field inside a current loop tends to be strong; outside, it tends to be weak. Magnetic storage media: --particulate g-Fe2O3 in polymeric film (tape or floppy) --thin film CoPtCr or CoCrTa on glass disk (hard drive) Note: For materials selection cases related to a magnet coil, see slides 22-11 to 22-15. It is called a tesla and its symbol is T. The coming slides will show how to write a tesla in terms of other SI units. Phys., Vol. J. J. Thompson used a CRT to discover the electron in 1897. If the substance is paramagnetic it weighs more in the magnetic field due to the same direction of magnetic field set in paramagnetic substance (attraction). O weak field outside strong field inside loop, directed into page strong field into page weak field. E fields affect any charge in the vicinity, but a B field only affects moving charges. They are temporary magnets. Current is the flow of positive charge. Each electron in an atom may be thought of as being a small magnet having permanent orbital and spin magnetic moments. The pairing of electrons cancels their magnetic moments You're already comfortable with the notions of charge and mass. The magnitude of the magnetic moment due to spin isBandis directed along the axis of the spin. The pics at the right show cross sections of a current carrying wire. = -Y2Zl i 14 -X2Zl)j +(XlY2 -x2Yl)k Note that the cross product of two vectors is a vector itself that is L to each of the original vectors. The bar magnet on the left is surrounded by iron filings, which orient themselves according to the magnetic field they are in. Although they look the same, they are different kinds of fields. Domains are ~ 10-30nm! Some examples of the ferroelectric solids are barium titanate (BaTiO3), Sodium potassium tartarate (Rochelle salt) and Potassium dihydrogen phosphate (KH2PO4)Note :All ferroelectric solids are piezoelectric but the reverse is not true. Select the correct answer and click on the Finish buttonCheck your score and answers at the end of the quiz, Visit BYJUS for all Chemistry related queries and study materials, Your Mobile number and Email id will not be published. The mag. Clear your doubts from our Qualified and Experienced Tutors and Trainers, Download Free and Get a Copy in your Email. North 1 1 South pole, How Solenoids Work The cross section of a solenoid is shown. As a certain amount of charge, q, moves with speed v through a wire of length L, the force of this quantity of charge is: F=qvxB Over the time period t required for the charge to traverse the length of the wire, we have: F = (q/ t) vtxB Since q/t=l and v t = L, we can write: F=1LxB where L is a vector of magnitude L pointing in the direction of I. chapter opening picture. (iv) Ferrimagnetic Substances:Substances which are expected to possess large magnetism on the basis of the unpaired electrons but actually have small net magnetic moment are called ferrimagnetic substances.Example: Fe3O4. Click Start Quiz to begin! A + charge at P feels a force out of the page. A - charge at R is moving up and to the left. A - charge at Q is moving out of the page. http://www.trifield.com/magnetic fields.htm Another good site for how magnets work http://bell.mma.edu/mdickins/TechPhys2/lectures3.html Equations and such http://schools.moe.edu.sg/xinmin/lessons/physics/default.htm See also: http://www.micro.magnet.fsu.edu/electromag/java/index.html http://www.micro.magnet.fsu.edu/electromag/java/detector/ How a metal detector works http://www.micro.magnet.fsu.edu/electromag/java/compass/ How a compass is oriented magnetically http://www.micro.magnet.fsu.edu/electromag/java/faraday2/ How Faraday did his current experiment http://www.micro.magnet.fsu.edu/electromag/java/harddrive/ How a hard drive works http://www.micro.magnet.fsu.edu/electromag/java/magneticlines/ How magnet lines is working http://www.micro.magnet.fsu.edu/electromag/java/magneticlines2/ How two magnets repel and attract http://www.micro.magnet.fsu.edu/electromag/j ava/nmr/populations/index.html Nuclear spin up/down http://www.micro.magnet.fsu.edu/electromag/java/pulsedmagnet/ Pulsed magnets http://www.micro.magnet.fsu.edu/electromag/java/speaker/ http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/elemag.html http://library.thinkquest.org/16600/intermediate/magnetism.shtml http://www-geology.ucdavis.edu/ge1161/sp98 burgmann/magnetics/magnetics.html http://www.micro.magnet.fsu.edu/electromag/java/index.html http://webphysics.davidson.edu/Applets/BField/Solenoid.html http://www.ameslab.gov/News/Inquiry/spring96/spin.html http://cfi.lbl.gov/budinger/medTechdocs/MRI.html http://www.wondermagnet.com/dev/images/dipole 1 .jpg.