are magnetic personalities always attractive? · robert a. schill, jr. lied discovery...

Are MAGNETIC Personalities Always Attractive?

Robert A. Schill, Jr.University of Nevada, Las Vegas

Dept. of Electrical and Computer Engineering4505 Maryland Parkway; Box 454026

Las Vegas, NV 89154-4026(702) 895-1526/4183 Lab: (702) 895-1430

FAX: (702) 895-4075e-mail: [email protected]

URL: http://www.ee.unlv.edu/~schill

Robert A. Schill, Jr. Lied Discovery Children's Museum, Las Vegas, NV [6/22/99]

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Dangerous Equipment

PLEASE FOLLOW DIRECTIONSIn some cases we will use high currentsIn other cases we will be using fireUnless directed DO NOT TOUCH

Some experiments may be performed at home

Always keep Mom or Dad informed on the experiment you want to perform before you conduct the experiment

Science is FUN when one is Careful


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What is a Magnetic Field?


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Early Philosophers - Webster’s World Encyclopedia 1999

300 BCThe Chinese Book of the Devil Valley Master refers to lodestone lining up with the earth's magnetic field.

?? BCDiscovery in the west that the lodestone attracts iron

270 ADChinese use compass for locating south

1044 ADChinese use compass for navigation

12 th CenturyArab physicist - “We know that the magnet loves the lodestone, but we do not know whether the lodestone also loves the magnet or isattracted to it against its will.”

Experiment - Sewing Needle Compass


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LODESTONE

Natural magnetic iron ore called magnetiteFirst known magnet. Iron filings are attached to this stoneIron oxide (rust) is seen on the right of the lodestone

Beulah Junior School Class 5P, Minerals, Crystals and their Properties,National Science, Engineering and Technology Week 13-22 March, 1998.


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More Recent Philosophers - Webster’s World Encyclopedia 1999

1600 William Gilbert Clearly explains that the earth behaves like a magnet in Gilbert’s De Magnete.

1635 Henry Gellibrand Reports that compass north varies from year to year in a given place, in a regular way.

1749 John Canton Develops a method for making an artificial magnet.1819 Hans Oersted Magnetic current affects a compass needle 1821 Michael Faraday Creates the first two electrical motors.1831 Michael Faraday Discovers electromagnetic induction, discovered

earlier but not published by Joseph Henry.1832 Joseph Henry Discovers transformer effect.1835 Michael Faraday Discovers self-induction, independently of Joseph Henry.1845 Michael Faraday Discovers the Faraday effect: a magnetic field makes

the plane of polarized light rotate.1873 James C. Maxwell Influenced (among other things) by Faraday.1966 various authors The earth's magnetic field is shown to reverse,

swapping north and south poles.1981 Blakemore & Frankel Discovery that bacteria have a magnetic sense.


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BUT BUT What is a Magnetic Field?


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Role PlayRole Play

Collisional force - Billiard Ball Force Force at a Distance


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Philosophical Question - Has no REALREALanswer!

We only experience the force created by the magnetic field.Philosophers/Scientists needed a way to make a connection between the object creating the force and the object experiencing the force.They devised (dreamed updreamed up) a mechanism or model to describe FORCE AT A DISTANCE.The magnetic field line was the mechanism which allows one to visualize a “force field” touching the object feeling the force.


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How is a Magnetic Field Generated?Magnetic Field Generated

By moving chargeBy current (which is a moving charge)

Like the very early Chinese, we will use a compass to examine the direction of the magnetic field.

Experiment - Current Generated Magnetic Field


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I

B

Orientation of Magnetic Field

Right Hand RulePlace thumb of right hand in the direction of currentFingers on right hand curl in the direction of the magnetic field

Valid for Long Straight WireUseful for Guessing at Field Orientation


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Force Acting on Parallel Wires Containing a Current

Experiment - Force Between CurrentsObservations

Direction of magnetic field generated by wire 1 at wire 2Direction of current in wire 2Direction of the force on wire 2What about wire 1? Does it move too? Which direction? Is this reasonable? Why?

Can we relate this to a Right-Hand-Rule?

B2X F1

I1

F1

Wire1

.

F2

I2F2

Wire2

B1


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Direction of Magnetic Force

I; Direction of Current at P

B; Direction of Magnetic Field at P

Direction of Force at Point P

P

Right Hand Rule for Force at P due to I & B

Point straightened fingers on right hand in the direction of the current at point PBend fingers in the direction of magnetic field at point PThumb on right hand points in direction of force experienced at P

B2X F1

I1

F1

Wire1

.

F2

I2F2

Wire2

B1


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If We Need A Current To Generate a Magnetic Field, Then How Do Magnets

Work?Magnets do not require batteries to work!Material EffectElectrons Exhibit

Orbital Motion

Spin Motion


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Model for Magnetic Materials - 1Imagine that Magnetic Material consist of many atomic current loops - (dipole moments, m)Originally in the absence of a magnetic field, the current loops are randomly oriented.In presence of a magnetic field, the current loops align in such a manner that the tiny magnetic fields, m, of each loop adds to that of the external field, B.

Electromagnetics by John D. Kraus, 4th edition, 1992.


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Model for Magnetic Materials - 2

Tiny atomic current loops cancel inside material if atomic loops are uniform

Yields a large loop current on outside of magnet due to atomic loop currents

NN

SS



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Permanent Magnet vs ElectromagnetPermanent Magnet - Experiment -Field Lines in 3-D Using Iron Filings

Does not require an external currentMaterial is hard to demagnetize (ceramic & aluminum-nickel-cobalt alloy (alnico))

Electromagnet - Experiment - Build Electromagnet

Magnetic field generated by an external current usually in the shape of a coil (solenoid) wrapped around a magnetic material (iron)When current is turned off, easy to demagnetize.


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Some Flavors of Magnetic MaterialsDiamagnetic - weakly repelsapplied magnetic field; orbital motion of electron dominates (Reverse Magnet - levitates) (Bismuth, Cu, H2O, gold) (Faraday 1846)Ferromagnetic - stronglyattracted by a magnetic field; electron spin align within each section (domain) of the material (iron, cobalt, nickel)

Paramagnetic - weaklyattracted by a magnetic field; orbit and spin magnetic moments compete. The magnetic moments align with the applied field causing the total field to be slightly increased. At high enough temperatures, all strong magnetic materials become paramagnetic.Experiment - Demagnetizing(aluminum, potassium)


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Is the Earth’s Magnetic Field Important?

The earth’s magnetic field shields the earth from harmful cosmic radiation.The earth’s field acts as a magnetic bottle. Ions are trapped in the atmosphere. Low frequency radio waves bounce off of these ions to other parts of the world.Appears to have a biological significance

N

SNGDC - National Geophysical Data Center


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How Solar Wind Affects the Earth’s Magnetic Field and Its Consequences.



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The Auroras Borealis -

Goddess of Dawn in the North

Luminous bands or streamers of light that are sometimes visible in the night skies of northern regions. They are caused by the ejection of charged particles into the magnetic field of the earth. (Northern lights).

Geo Data Center from the University of Alaska Fairbanks


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About a 10% Decline in the Earth’s Magnetic Field Over a 100 Year Period

Magnetic (North/South) pole reversal are commonOccurs about once every half a million years or soCurrently unable to predict next pole reversalLast field reversal occurred about 700,000 years ago

1900 2000National Geophysical Data Center


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Do Magnetic Fields Affect Animals and People?

BioelectromagnetismLiving things

AstronautsPigeonsSalamandersTadpolesHoney beeBacteria


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Salamanders Fall Asleep (Anesthetized) in Large Magnetic Field

Robert Becker (1963)At 3,000 G the animal was motionless and unresponsive to all stimuli - EEG (electroencephalogram) showed simple delta brain waves Decreasing the magnetic field the animal recovered within seconds - Normal EEGNo apparent side effects

The Body Electric Electromagnetism and theFoundation of Life, R.O. Becker and G. Selden,

Morrow Publications, 1985.


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Cosmonauts (Soviet Astronauts), Pigeons, Honeybees, and Bacteria

Honing Pigeons - navigated by earth’s magnetic field even when sun is shiningEarly cosmonauts experienced bone-calcium loss and muscle cramps in space above the earth’s magnetic for an extended amount of time.

Health maintained when artificial magnetic fields were placed in space capsule

Honey bees disoriented in large magnetic fieldsFreshwater Bacteria cultured in an iron rich medium travel either North or South

Contain magnetite like particles


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UNLV Research: Interaction of DC & 60 Hz Magnetic Fields With Tadpoles

UNLV Research - Dr. Karin Hoff and Dr. Robert Schill, Jr.

Designed and built magnetic coilsSolenoid CoilHelmholtz Coil

Respond?How?Why?


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Exp. Set-up and Tentative ConclusionsBody posture of tadpole is sensitive to magnetic fieldTadpoles feel presence of small magnetic fields - less than 1/7 of earth’s field

Earth’s magnetic field - 0.5 GHair Dryer - 0.3 G at 6”Vacuum Cleaner 0.06 G at 1’Analog Clock 0.015 G at 1’

Tadpole

Eye


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Film Clip & Current Research GoalWhat Health Benefits Exist?

Mechanism?Film Clip

0-30 min Field Off30-60 min; 0.07 G 60 Hz Field On

Picture from: This Week in Green Valley PaperNov. 21, 1997.

Dr. Hoff & Schill’s ResearchJune 1999.


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Some Interesting Applications of Magnetic Fields

Ore SeparationMagnetic Levitation (MAGLEV) VehiclesPulse Power Nuclear Fusion


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Ore SeparationElectromagnetic is typically usedAt Room Temperature, the only materials with strong magnetic properties are Iron, Cobalt, and Nickel AlloysAluminum, Copper, etc.: NOT magnetic.Would you touch Would you touch that?that?


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MAGLEV vs Other Forms TransportationA fast, inexpensive means of transportation is crucial in today’s business and society.Typical Travel Speeds for Various Modes of Transportation

Walking - 2 mph roughly (~ 15 to 20 miles per day)Horse - roughly 30 miles per day comfortablyCar - 55 to 70 mphPlane - 360 mph on averageMAGLEV - 250 to 300+ mph in near future

~ 1/3 Travel Energy Cost of a conventional planeGreen Transportation Technology - minimal air and noise pollution


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How MAGLEV Vehicles Float

Electrodynamic, repulsion-type --American/JapanLevitation magnets on top of a guide railSuperconducting magnets on bottom side of vehicle (15 cm air gap)

Electromagnetic, attraction-type -- GermanConventional iron-core magnets on the vehicleAttracting magnets under the guide rail (1cm air gap)

The EPRI Journal:Jan./Feb. 1997Vol. 22, No. 1.


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Different MAGLEV Designs

Swissmetro Project

The EPRI Journal: January/February 1997 Vol. 22, Number 1.


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Fusion Process

Forcing together Deuterium and Tritium nucleiFuse into a form of HeliumEmits large amount of energy

G. Yonas, Fusion and the Z Pinch, Scientific American, Aug. 1998.


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Pulse Power Fusion Process

G. Yonas, Fusion and the Z Pinch, Scientific American, Aug. 1998.


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A Successful Mechanism Leading to Pulsed Power Fusion - Z Pinch

J x B

B

I

Plasma

J x B

B

I

Ir

rc

Plasma

Rigid ReturnConductor

Z-Pinch Mechanism Z-Pinch Coaxial Geometry


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Building a Wire Array - Close-Up View

Wire Array - Single/Double~1/10 th Dia. human hair0.7 microns thickArray dia. ~ shot glass

Wire MaterialAl, Ti, Cu, W (Tungsten)

The pictures on this slide and the next three or four slides are fromSandia National Laboratory in Albuquerque, New Mexico.


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Cartoon Picture of PBFA-Z or Z


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PBFA-Z or Z


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ARCS AND SPARKS: OPEN SHUTTER PICTURE Z


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Time Varying Fields

Static (Non time varying) models begin to loose their meaning as the fields change slowly from a constant state to a time varying state.Electric and Magnetic fields are linked together - are oneThe greater the fields with time, the stronger the link.


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What Does This Link Mean?

The Electric Field and the Magnetic Field feed off of each other.The Electric and Magnetic fields circulate or link with each other.This is the key to understanding how light and radio waves propagate through space (radiation) with-out a source on.

This implies that a time varying magnetic field may generate (induce) a voltage in a circuit. A time varying electric field may generate (induce) a current in a circuit.Recall in Static theory

Magnetic fields were linked only to currentElectric fields are linked only to voltages (potential differences)

E-FieldB-Field

E-Field


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How Do The Fields Change?

Nature resists change.Nature resists change.Induced voltages and currents are generated in such a manner that it supports the field that was present a moment ago.Real quantities take time to change. Einstein said that nothing can travel faster than the speed of light. This statement of causality implies that the chicken can never come before the egg.

Role PlayRole Play


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Transformer Action - Magnetic Field Varies with Time and Medium is Stationary

Experiment - Underwater LightA time varying magnetic field generates (induces) a voltage in a second coil which in turn drives a current to light the light bulb.The time varying magnetic field may be thought of as the voltage source (electromotive force) for the second circuit.

v(t)

LightBulb

B (t) Decreasing with t1

Coil 11I

2ICoil 2


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Motional Action -Magnetic Field Constant and

Medium MovesExperiment - Electromagnetic Catapult & Electromagnetic BrakeThe number of magnetic field lines enclosed by the circuit changes. A current is generated in the circuit to oppose this change.The moving circuit may be thought of as being the voltage source for the circuit.If a physical battery is placed in the circuit, the moveable rod will exhibit motion.

Direction ofMotion

Direction ofMotion

B

+

I

-

B


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are magnetic personalities always attractive? · robert a. schill, jr. lied discovery...

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