MagnetismWhat is it and why are

“they” saying such nasty things about it?

Daryl L TaylorDTFizzix.com

Greenwich HS, CT02/21/2012

Why are we here?

•We should learn –Where does magnetism come from?–How it relates to electricity?–What does it have to do with real life?–Watch floating fruit?

Electricity & Magnetism Related?• So much so, you simply can’t have one without

the other.– ‘+’ & ‘-’ relates to ‘N’ & ‘S’

• A moving magnet will cause a motion of charges. [Induction DEMO!] (and verse visa…)

• Magnetic Fields are caused by moving electric charges. [Current-bearing wire DEMO!]

• [Electromagnet]

Recall Angular Momentum?(Before we get carried away with all this Magnetism

nonsense…)

Recall Angular Momentum?(Before we get carried away with all this Magnetism

nonsense…)• Spinning wheel/Hoberman/ShopVac DEMO thingee?–Why?• ‘L’ must be conserved.• You feel a ‘tug’ in the opposing direction.• You spin in the opposite direction

• Magnetic Moment is analogous!

mrvLr

vmrIL

2

2

2

22

2

2

1

2

1

2

1

mvKE

r

vmrKE

IKE

ROT

ROT

ROT

Another vicious Right-Hand Rule…

• Most atoms have single electrons or paired electrons that ‘spin’ in opposite directions.• This ‘cancels’ any effective magnetic field.

• Sorta like a wheel rotating in BOTH directions at once…• Helicopter…

• However, some – like iron, cobalt, nickel – have paired electrons that spin in the same direction. NOTE: LEFT HND e-…• Thus, adding magnetic “strengths”.

Angular MomentumL=I

Magnetic MomentIA

Ferromagnetic Elements

• Strongly attracted in magnetic fields– Fe– Ni– Co– Gadolinium (#64)– Dysprosium (#66)– Holmium (#67; strongest of all…)

Paramagnetic Elements

• Weakly attracted in magnetic fields– Platinum– Al– O

Diamagnetic Elements

• Weakly repelled by BOTH poles– C– Cu– H2O (I know, not an element, but…)

Magnetic Field?

• Sorta the same as E Fields–Area around an electric charge where

another charge feels a force.• E=F/Q

• Mag Field–Area around a magnet where another

magnet, paramagnet, or diamagnet feels a force. • Math is weirder…

MB

H oo

Mini-LABMapping a Field

3-D Field DEMO

Mag Field around a wire

Mag Field around a loop

Radius of charge in B

Why? Lentz, that’s why!

E vs B Fields

Lorentz Force Law

Ugly RT Hand Rule

Current in B

Mass Spec

Misc Demos

• Lentz Law• Spinny Thingee• TV Destruction• Lifter Magnet• Magnetic Levitation–Biggee & Cutie

Misc Demos

• Plasma Globe –With Fluorescent Tube! DANGER!

• Plasma Disc• Generator flashlights• Incandescent Bulb w/magnet• Conservation of L Disc–Volunteer!

MAFF…

MAFF…

sinF IlB Force on electric current in magnetic field…

Ex 20-1 p512

MAFF…

sinF qvB Force on moving charge in magnetic field…

Ex 20-3 p514

MAFF…

2

F ma qvB

mvqvB

rmv

rqB

Example 20-4 p514

MAFF…

2o

IB

rI

Br

Aurora Thingee

Aurora Thingee

Aurora Thingee

Aurora e- levels

Ahh, But!!!!

In reality…

N

S

Earth’s Magnetic Field??What science tells us?

+5000 yrs

Earth’s Magnetic Field??What science tells us?

+10,000 yrs

Earth’s Magnetic Field??What science tells us?

+20,000 yrs

Magnetic File Cabinet DEMO?

Lodestone!

Core #’s• Inner Radius = 1200 km• Outer Radius = 3470 km• Tboth = 24 hrs

• Massinner= 0.02 Mearth

• Massouter = 0.31Mearth

– Find Kerot of core!

Jx

daymxkgx

mr

IKRot

32

22624

22

2

105

1

21047.310633.

5

1

5

2

2

12

1

5x1032J Analogies?

• About the amount of energy the entire Sun emits in 100 seconds. That's a whole lot of energy.

• If it doesn't sound like much, let's convert it to megatons: it's the equivalent energy of five trillion one megaton bombs

5,000,000,000,000 MILLION TONS TNT!going off at once. That is comfortably more than

the entire arsenal of the planet. – In fact, it's about 500 million times the explosive energy

of every single nuclear weapon* on the Earth.• *That we know of…

So, why were we here?

•We learned –Magnetism is created by moving

charges• Analogous to Angular Momentum

–Conversely, a changing magnetic field creates a current.• Electric generators

– The earth is the largest magnet around?– Fruit and small animals can levitate?

So, why were we here?

•We learned –Not all magnetic fields are nice and pretty–Magnetic properties of an object are dictated by it’s domains.–Not everyone knows the $100 answers!