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ES Lesson 5 • • • • What is a magnet? What is a magnetic force field? What is an electromagnet? What is a magnetic coil? © 2012 C. Rightmyer, Licensed under The MIT OSI License, 20 July 2012 (1600) William Gilbert writes “De magnete” • Physician to Queen Elizabeth I. • Studied electric attraction, electric force, and magnetism over his entire lifetime. Recorded his research and experiments in a 6-book treatis on these subjects. • After experiments with a terrella (spherical magnet), he proposed that the earth is a giant magnet. • Coined term “electricity” from the Greek word for amber. • Guessed correctly that iron can be temporarily magnetized by induction. What is a magnet? Electricity and Magnetism, Gareth Stevens Publishing, Steve Parker, 2007 ES project 5-1. Magnetic attraction and repelling [Intro to College Physics, Appleton-Century-Crofts, R.D. Rusk, 1960] The earth itself acts like a magnet [Intro to College Physics, Appleton-Century-Crofts, R.D. Rusk, 1960] ES project 5-2. Make a compass Push the magnetised sewing needle lenthwise through the cork. Place the cork into a bowl of water. The cork will rotate to point towards the north. [Science Action Labs TLC10207 Electricity and Magnetism, Teaching and Learning Co,, Edward Shevick, , 2000] ES demo 5-3. A bar magnet dipped in iron filings [Intro to College Physics, Appleton-Century-Crofts, R.D. Rusk, 1960] ES demo 5-4. Magnetic force field about a bar magnet [Intro to College Physics, Appleton-Century-Crofts, R.D. Rusk, 1960] ES demo 5-5. What happens to a bar magnet if broken into several pieces? [Intro to College Physics, Appleton-Century-Crofts, R.D. Rusk, 1960] ES demo 5-6. Attractive force between opposite poles [Intro to College Physics, Appleton-Century-Crofts, R.D. Rusk, 1960] ES demo 5-7. Repelling force between same type pole. [Intro to College Physics, Appleton-Century-Crofts, R.D. Rusk, 1960] ES demo 5-8. Magnetic induction in action [Adapted from an idea presented at http://www.phy6.org/earthmag/inducemg.htm] ES demo 5-9. Use a compass to observe magnetic field direction. Strong Weak Strong Weak [Intro to College Physics, Appleton-Century-Crofts, R.D. Rusk, 1960] ES demo 5-10. Hans Christian Orsted’s accidental discovery BE demo 1-11 + 9 volts A stronger magnetic field is generated when the wire is formed into a coil + + Electromagnetic field induced by current Magnetic field adds in center of circular coil L (in microHenrys) = (approximately) D^2 x N^2 / [(18xD) + (40xW)] Adapted from Make: Electronics, O’reilly [Publishing], Charles Platt, 2009 The magnetic field in a conducting coil is like that of a cylindrical permanent magnet. Electricity and Magnetism, Gareth Stevens Publishing, Steve Parker, 2007 ES project 5-11. Make an electromagnet by winding a coil around a steel nail. BE demo 1-12 3 volts [Teaching Electricity, Scholastic Professional Books, Steve Tomecek, 1999] L3 Background slides Compressing the coil generates a magnetic field much like a button magnet. [Intro to College Physics, Appleton-Century-Crofts, R.D. Rusk, 1960] Making your own compass [Science Action Labs TLC10207 Electricity and Magnetism, Teaching and Learning Co,, Edward Shevick, , 2000]