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 observemagnetic field direction.

[Intro to College Physics, Appleton-Century-Crofts, R.D. Rusk, 1960]

StrongStrong

Weak Weak

ES demo 5-10. Hans Christian Orsted’s accidental discovery

+

9 volts

BE demo 1-11

A stronger magnetic field is generated when the wire is formed into a coil

Adapted from Make: Electronics, O’reilly [Publishing], Charles Platt, 2009

Electromagnetic fieldinduced by current

++

-

Magnetic field adds incenter of circular coil

L (in microHenrys) = (approximately) D^2 x N^2 / [(18xD) + (40xW)]

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.

[Teaching Electricity, Scholastic Professional Books, Steve Tomecek, 1999]

3 volts

BE demo 1-12

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]