Physics Presentation. Magnets.
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible and causes the most notable property of a magnet: a force that pulls on nearby magnetic materials, or attracts or repels other magnets. The structure of the invisible magnetic field of a magnet is made visible by the pattern formed when iron filings are scattered around the magnet, as in the accompanying figure.
- Hard or Permanent Magnetand- Soft or Impermanent Magnet
Eg. Liquid Oxygen
Eg. A traditional refrigerator magnet
Ferrimagnetic retain their magnetization in the absence of a field.
However, like antiferromagnets, neighboring pairs of electron spins like to point in opposite directions.
These two properties are not contradictory, due to the fact that in the optimal geometrical arrangement
A solenoid is a three-dimensional coil. In physics, the term solenoid
refers to a loop of wire, often wrapped around a metallic core, which
produces a magnetic field when an electric current is passed through it.
Solenoids are important because they can create controlled magnetic
fields and can be used as electromagnets.
The knowledge of static electricity dates back to the earliest civilizations, but for millennia it remained merely an interesting and mystifying phenomenon, without a theory to explain its behavior and often confused with magnetism. The ancients were acquainted with other curious properties possessed by two minerals, amber and magnetic iron ore. The former, when rubbed, attracts light bodies : the latter has the power of
Based on his find of an Olmec hematite artifact in Central America, the American astronomer John Carlson has suggested that "the Olmec may have discovered and used the geomagnetic lodestone compass earlier than 1000 BC". If true, this "predates the Chinese discovery of the geomagnetic lodestone compass by more than a millennium“.
Isaac Newton contended that light was made up of numerous small particles. This could explain such features as light's ability to travel in straight lines and reflect off surfaces. This theory was known to have its problems: although it explained reflection well, its explanation of refraction and diffraction was less satisfactory. In order to explain refraction, Newton's Opticks (1704) postulated an "Aethereal Medium"
In 1752, Benjamin Franklin is frequently confused as the key luminary behind electricity. William Watson and Benjamin Frankilin share the discovery of electrical potentials. Benjamin Franklin promoted his investigations of electricity and theories through the famous, though extremely dangerous, experiment of flying a kite through a storm-threatened sky. A key attached to the kite string sparked and charged a
In 1800 Alessandro Volta constructed the first device to produce a large electric current, later known as the electric battery. Napoleon, informed of his works, summoned him in 1801 for a command performance of his experiments. He received many medals and declarations, including the Légion d'honneur.
Davy in 1806, employing a voltaic pile of approximately 250 cells, or couples, decomposed potash and soda, showing that
In the first half of the 19th century many very important additions were made to the world's knowledge concerning electricity and magnetism. For example, in 1819 Hans Christian Oersted of Copenhagen discovered the deflecting effect of an electric current traversing a wire upon- a suspended magnetic needle.
This discovery gave a clue to the subsequently proved intimate relationship between electricity and magnetism which was promptly
1. Two parallel portions of a circuit attract one another if the currents in them are flouring in the same direction, and repel one another if the currents flow in the opposite direction.
2. Two portions of circuits crossing one another obliquely attract one another if both the currents flow either towards or from the point of crossing, and repel one another if one flows to and the other from that point.
Hans Christian Oersted
In 1853 Sir William Thomson (later Lord Kelvin) predicted as a result of mathematical calculations the oscillatory nature the electric discharge of a condenser circuit. To Henry, however, belongs the credit of discerning as a result of his experiments in 1842 the oscillatory nature of the Leyden jar discharge. He wrote:The phenomena require us to admit the existence of a principal discharge in one
In 1896 J.J. Thomson performed experiments indicating that cathode rays really were particles, found an accurate value for their charge-to-mass ratio e/m, and found that e/m was independent of cathode material. He made good estimates of both the charge e and the mass m, finding that cathode ray particles, which he called "corpuscles", had perhaps one thousandth of the mass of the least massive ion known (hydrogen).
short for magnetic levitation, is a type of high-speed train that hovers over the track and uses electromagnets to propel it along the track. There are three basic components of the trains: a large electrical power source, metal coils lining the track, and large magnets attached underneath the train, which are used to guide it along the track and allow it to levitate. Since the trains do not actually touch the track, there is no friction present. This enables the train to reach speeds of approximately 300 mph. This also reduces the noise and vibrations common on other types of similar transportation.
1. Electrodynamic Suspension System
2. Electromagnetic Suspension System
The electrodynamic system, also known as the Linear express, was developed in Japan. The electrodynamic system is based on three basic principles, Lenz's law (motional emf), moving current creates a magnetic field, and that like poles of a magnetic field repel while opposite poles attract. Superconducting wires are used in a basically solenoid shape to create the electromagnets on the train with a linear synchronous motor that provides the alternating current.
Track of Linear Express train in a tunnel
Linear Express train, model MLX01-901
Trains propelled by electrodynamic suspension system levitate over the track with a distance of about 8-10 cm while the electromagnetic system only hovers at 1-2cm above the track. The levitation in the electrodynamic system depends upon induced currents caused by the movement of the train's electromagnets and the levitation coils on both sides of the track. Remember when a magnetic field changes over time, an induced current is created opposing the changing magnetic field.
The reason the train doesn't get stuck on the side of the track isbecause of Lenz's law and induced currents! Guidance, the name for this induced current, opposes sideways motion of the train and keeps the train in the middle of the track. Guidance coils may be the levitation coils, or located underneath the levitation coils. Since the electromagnet is a solenoid, recall the intensity is largest very close to the center of the solenoid. When the electromagnet moves close to one side of the track, an induced current occurs because the intensity of the magnetic field increases.
The propulsion system moves the train forward, and is different from the levitation and guidance system. The propulsion coils in the track have an ac current that propagates down the track in front of the train. This alternating current creates an opposite magnetic field to the electromagnet, and since opposite poles attract, the electromagnet pulls the train moves forward. The alternating current also creates a repulsive force at the back of the electromagnet, helping push the train forward.
The Electromagnetic Induction Suspension System, also known as the Transrapid System (to go commercial In 2005), was tested and developed in Germany after being first conceived by Graeminger with a patent in 1934 by Herman Kamper. The first test vehicle called the "Principle Vehicle" had a maximum velocity of 90 km/h and was developed in 1971 on a 600 meter track. Starting in 1972 Germany also developed and tested an Electrodynamic System (EDS) which could be considered the forefather of
A train that uses permanent magnets is in an unstable equilibrium. As such, the train will not return to the center of a rail. Rather, it will, without secondary assistance (such as with an EDS system), kilter off to one side. So it is a combination of magnets as well as technology that allows the Maglev machines that ARE feasible to work. It is the use of electromagnets that allows an unstable equilibrium to become a stable equilibrium.
Although some people are concerned about the effect of the electromagnetic field upon humans, according to scientists the magnetic field felt in the cabin is not strong enough to have a significant effect upon humans, especially when compared to the magnetic field created by other electrical appliances. Since the magnetic field induced by the solenoid is weak in the area above the solenoid, the magnetic field experience in the cabin is much weaker than the magnetic field between the sides of the train and track.
Superconductors are expensive, but since at optimal, cool temperature there is no resistance in the superconducting wires, the generator required to create the needed magnetic force is smaller and lighter than the generator would need to be with normal wires. Other materials could also be used, but their effectiveness would not be as good as the superconductors. One method to keep the superconductor is kept cool by a small helium refrigerator surrounding each solenoid.