Braunbeck’s extension (1939) states that a system of permanent magnets must also contain diamagnetic material or a superconductor in order to obtain stable, static magnetic levitation or suspension. Likewise, due to limitations on permittivity, stable suspension or levitation cannot be achieved in a static magnetic field with a system of permanent magnets or fixed current electromagnets. Samuel Earnshaw was the one to discover in 1839 that “a charged body placed in an electrostatic field cannot levitate at stable equilibrium under the influence of electric forces alone”. The application of magnetic levitation is most commonly known for its role in Maglev trains. It also avoids wear and has very low maintenance requirements. Magnetic levitation technology is important because it reduces energy consumption, largely reduces friction. Many systems use magnetic attraction pulling upwards against gravity for these kinds of systems as this gives some inherent lateral stability, but some use a combination of magnetic attraction and magnetic repulsion to push upwards. In EMS a feedback loop which continuously adjusts one or more electromagnets to correct the object's motion is used to cancel the instability. Although static fields cannot give stability, EMS works by continually altering the current sent to electromagnets to change the strength of the magnetic field and allows a stable levitation to occur. In these kinds of fields an unstable equilibrium condition exists. In most cases the levitation effect is mostly due to permanent magnets as they don't have any power dissipation, with electromagnets only used to stabilize the effect.Īccording to Earnshaw's Theorem a paramagnetically magnetised body cannot rest in stable equilibrium when placed in any combination of gravitational and magnetostatic fields. Magnetic levitation with a feedback loop.Įlectromagnetic suspension ( EMS) is the magnetic levitation of an object achieved by constantly altering the strength of a magnetic field produced by electromagnets using a feedback loop. It should use a crank and have fewer than 10 wraps of wire.Suspension of objects through a feedback loop of magnetic field strength changes Floating globe. It should have 10 wraps of wire and a magnet that is moved up and down by hand. It should have 35 wraps of wire and have a crank that turns slowly. It should use a crank and have at least 50 wraps of wire. What should be true about this generator? A. The recorded maximum voltage corresponds to the amount of electricity generated.Prototype 1Prototype 2Wire Coil10 wraps50 wrapsMax Frequency4 Hz2 HzMax Voltage2 mV3 mVThe students want to combine the strengths of each prototype to create a generator that works better than either. The recorded maximum frequency relates to how fast the magnet or the coil was able to move. The students' data is shown in the table below. They noticed that the faster the magnet or coil moved, the higher the voltage was. These prototypes are shown below.The students tested their prototypes and collected some data. In prototype 2, a magnet is moved up and down by hand through a coil of wire. In prototype 1, a hand crank is used to spin coils of wire past the magnets. In a science class, the students built two different prototypes for an electric generator. a motor made with 0.4 mm copper wire wrapped 5 times around the iron core a motor made with 1.2 mm copper wire wrapped 15 times around the iron core D. a motor made with 0.4 mm aluminum wire wrapped 15 times around the iron core C. a motor made with 1.2 mm aluminum wire wrapped 5 times around the iron core B. Which of the following would most likely have the fastest rate of rotation? A. The table below describes each student's motor.Electric Motor DesignsStudent NameNumber of Turnsin Electromagnet'sWire CoilMaterial of Wire CoilThickness of Wire Used in CoilRate at Which the Motor SpinsLupe15copper0.4 mm17 turns in5 secondsSanjay5aluminum0.4 mm4 turns in5 secondsOliver5copper1.2 mm21 turns in5 secondsRebekah15aluminum1.2 mm11 turns in5 secondsFelipe15aluminum0.4 mm7 turns in5 secondsBased on the data collected, the students are going to design a new motor that incorporates the best parts of each individual motor. Each motor was connected to the same voltage source, and the number of turns the motor made in 5 seconds was counted. Peterson's class each designed a simple electric motor using a permanent magnet and an electromagnet made up of a coil of wire wrapped around an iron core.
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