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ES Lesson 5
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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]