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Magnetic poles, Magnetic fields, Magnetic domains, Electromagnet, Electric Motors, AC Current, Faraday's Law of Induction, Electric Motors, Right hand rule, Magnetic Resonance Imaging (MRI)

Skyler Saucedo

on 3 May 2010

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Transcript of Magnetism

Double click anywhere & add an idea Magnetic fields Magnetic Domains Electromagnetism Electric motors AC Current Michael Faraday Induction Right Hand Rule Magnetic Resonance Imaging Magnetic Force One of the first drawings of a magnetic field, by René Descartes, 1644. It illustrated his theory that magnetism was caused by the circulation of tiny helical particles, "threaded parts", through threaded pores in magnets. Precipitator, stack

* Burning coal produces carbon dioxide (CO2), sulfur dioxide (SO2) and nitrogen oxides (NOx).
* These gases are vented from the boiler.
* Bottom ash, which is made of coarse fragments that fall to the bottom of the boiler, is removed.
* Fly ash, which is very light, exits the boiler along with the hot gases.
* An electrostatic precipitator (a huge air filter) removes 99.4 per cent of fly ash before the flue gases are dispersed into the atmosphere.

5. Turbine, generator

* Water in the boiler tubes picks up heat from the boiler and turns into steam.
* The high-pressure steam from the boiler passes into the turbine (a massive drum with thousands of propeller blades).
* Once the steam hits the turbine blades, it causes the turbine to spin rapidly.
* The spinning turbine causes a shaft to turn inside the generator, creating an electric current. Magnetism Lodestone At 5th Cent. BC - Greeks (Magnesia) knew about magnets (iron oxide)

1100 AD - Chinese use needles of magnetite to make compasses

13th Cent - Magnetites have two places of maximum attraction (poles)

Electricity = Magnetism / in electricity, you can choose polarity

in magnetism, poles always come in pairs magnetic monopoles do not exist How do we define electric monopoles? 16th Cent - Earth's Magnetic Field is mapped Hans Christian Ørsted On 21 April 1820, during a lecture, Ørsted noticed a compass needle deflected from magnetic north when electric current from a battery was switched on and off, confirming a direct relationship between electricity and magnetism. His initial interpretation was that magnetic effects radiate from all sides of a wire carrying an electric current, as do light and heat. Three months later he began more intensive investigations and soon thereafter published his findings, showing that an electric current produces a circular magnetic field as it flows through a wire. This discovery was not due to mere chance, since Ørsted had been looking for a relation between electricity and magnetism for several years. The special symmetry of the phenomenon was possibly one of the difficulties that retarded the discovery. 19th Cent. Discovery

Ørsted's discovery prompted an explsion of discovery in Physics:

André-Marie Ampère quantifies magnetic field and electric current

Michael Faraday and his laws of Induction and Voltage

and James Clerk Maxwell's universal theory of Electromagnetism
Now for some formalism o x . B _ ` magnetic field vector vector comes out of page vector goes into page Also known as:

Right Hand Corkscrew Rule - Walter Levin RHR - 1st developed by John Ambrose Fleming in the late 1800s Also follows RHR Note on using RHR:

Thumb always points in the direction of current

Curl fingers in direction of magnetic field movement

Force will point in the direction of index finger Predict movement of wire using RHR! Magnetic Force between two parallel wires Can we predict the behavior? How do we measure the strength of the magnetic force? Lorentz force F = v x B B V - velocity of charge

B - Magnetic field strength The electrical conductivity of the molten plasma of the Earth's core should be able to damp the current magnetic field in only thousands of years. Yet our five billion year old Earth clearly causes magnets to point to (defined) north. The mystery is still being studied but recently thought related to motions in the Earth's liquid outer core. Specifically, as portions of the outer core cool and fall inward, oceans of the liquid iron-rich magma rise outward, forced into a helical motion by the spin of the Earth. This motion, many geologists now believe, regenerates Earth's magnetism. Pictured above, a computer simulation shows the resulting magnetic field lines out to two Earth radii, with blue lines directed inward and yellow lines directed outward.
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