(21) Magnetic Forces and Magnetic Fields

(21) Magnetic Forces and Magnetic Fields - Lecture Notes 21...

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Magnetic Forces and Magnetic Fields Lecture Notes 21
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Goals To observe and visualize magnetic fields and forces. To study the motion of a charged particle in a magnetic field. To evaluate the magnetic force on a current-carrying conductor. To determine the force and torque produced with a magnet and current-carrying loop of wire (the DC motor). To study the fields generated by long, straight conductors. To observe the changes in the field with the conductor in loops (forming the solenoid). To calculate the magnetic field at selected points in space. To understand magnetism via magnetic moments.
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Historical Notes - Lodestone (magnetite mineral): ± The name "magnet" comes from lodestones found in a place called Magnesia. ± A piece of intensely magnetic magnetite that was used as an early form of magnetic compass. ± Only magnetite with a particular crystalline structure , lodestone, can act as a natural magnet and attract and magnetize iron . In China, the earliest literary reference to magnetism lies in a 4 th century BC book called Book of the Devil Valley Master : "The lodestone makes iron come or it attracts it." The earliest mention of the attraction of a needle appears in a work composed between 20 and 100 AD. ± From amusement and magic-like to application “leading stone” (lodestone) – compasses and navigation . ± By the 12 th century the Chinese were known to use the lodestone compass for navigation. ± Today’s powerful lodestones and magnetic materials are ubiquitous .
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What if no lodestones existed? The Chinese would certainly not have invented the magnetic compass. Magnetism would have been discovered much later, and one wonders how. Lacking the compass, the great voyages of discovery could hardly have taken place--Columbus, De Gama, Magellan and the rest. The history of the world might have been quite different! Magnetic Jewellery Magnetic energy is the strongest natural force in the universe and the power of magnets is one of the most basic powers of nature. The use of magnet therapy for health and well-being has an ancient history dating back thousands of years. Ancient Egyptians used loadstones to prolong life and improve health. It is said that Cleopatra wore a polished lodestone on her third eye, in the belief that it helped maintain her youth and beauty. In more recent times, Paracelsus (1493-1541) considered to be the father of modern medicine, believed that the "life force' of the body was most influenced by the force found in magnets. In Europe, Russia, China, Japan and many other countries, convinced of the benefits, millions of people continue to use magnet therapy. Today, we are experiencing an exciting revival of this ancient therapy. Resulting from the impact of more and more clinical studies and anecdotal evidence, 120 million people worldwide spend over $1.5 billion globally on the therapeutic benefits of magnets.
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Two experiments, different scale: Although the magnet on the left is an electromagnet (huge) and the one on the right is a permanent magnet (small), the idea is the same.
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Examples of Magnetic Fields Fields are created in a variety of ways and observed in a variety of places.
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This note was uploaded on 04/01/2011 for the course PHY 135 taught by Professor Wagihghobriel during the Spring '11 term at University of Toronto- Toronto.

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(21) Magnetic Forces and Magnetic Fields - Lecture Notes 21...

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