Electricity and Magnetism

ELECTRICITY AND MAGNETISM

PHYSICS IS PHUN - January 2005

Welcome and Thanks Comment: Basic ideas in electricity and magnetism Review fundamental laws of Electricity and Magnetism summarized in Maxwell’s equations

STATIC ELECTRICITY

S All of you have played around with static electricity (E1-1.1) Comment: Origin of electricity is atomic: positive nucleus with protons and neutrons electrons surrounding nucleus atoms are neutral - same number of p’s and e’s

Neutrons are neutral - effect mass of atom but less effect on chemical properties

S Pity the poor neutron……(A1-1.83)

Separation of charges by “friction” actually CONTACT - “triboelectric” effect

S Compare triboelectric effect with siphon (E1-3.6) Comment: Actually quantum mechanical “tunneling”

D J1-01 TRIBOELECTRICITY - CHARGING BY FRICTION Charge electrometer with glass rod (+) and with hard rubber rod (-) Examples: shoes on rug, woolen coat on plastic car seat

S Another example (E1-1.2)

CHARGING BY CONDUCTION AND INDUCTION

S Charging by induction (leave slide on during demo) (E1-3.5) D J1-12 INDUCTION - ELECTROSCOPE Charge by induction and check by bringing glass rod close

D J1-11 ELECTROPHORUS (page 2)

POLARIZATION

D J4-11 POLAR AND NONPOLAR LIQUID

D J4-12 ELECTROSTATIC FORCE - MOVING LUMBER

Comment: polarization important in biological phenomena, eg human body, and how microwave oven works

VAN DE GRAAFF GENERATOR

D J2-03 VAN DE GRAAFF GENERATOR WITH GROUND SPHERE

D J2-14 LIGHTNING ROD SIMULATOR

6S Lightning slide set: (E1-2.5 thru 2.10) Charge separation in clouds - mirror on ground Leader develops Lightning discharges along path of leader Prevent lightning using lightning rod

MAGNETS

D J7-01 LODESTONE

MAGNETIC FORCES

D TWO BAR MAGNETS ON OVERHEAD PROJECTOR (page 3)

RELATION BETWEEN ELECTRICITY AND MAGNETISM Summarized in four equations known as “Maxwell’s Equations”

AMPERE’S LAW Electric currents create magnetic fields

Shown in pre-show S Right hand rule (E3-1.2) D K1-05 FORCE BETWEEN CURRENT-CARRYING COILS Examples: electromagnets, motors

LORENTZ FORCE Charges moving in a magnetic field experience an electromagnetic force

S Left Hand Rule (E3-1.1) D K1-12 CATHODE-RAY TUBE - DEFLECTION BY MAGNET D K1-03 FORCE ON CURRENT IN MAGNETIC FIELD Examples: loud speakers, particle accelerators (cyclotron, synchrotron)

FARADAY’S LAW OF INDUCTION A changing magnetic field creates an electric field

D K2-04 FARADAY'S EXPERIMENT - EME SET - 20, 40, 80 TURN COILS D K2-01 EARTH INDUCTOR with red magnet Examples: generators, transformers, dynamic microphone

LENZ’S LAW Induced magnetic fields act so as to oppose the motion that caused them

D K2-44 EDDY CURRENT PENDULUM Cool pendulum with LN D K2-42 LENZ'S LAW - MAGNET IN ALUMINUM TUBE S Magnets dropped through tube (E4-2.4) Examples: magnetic damping in balance, speedometer damping (page 4)

COMPLEX ELECTROMAGNETIC PHENOMENA

D K2-61 THOMSON'S COIL Student holding down ring Shoot ring - with and without LN Example: magnetic levitation trains

D K2-62 CAN SMASHER - ELECTROMAGNETIC Give explanation then blast can Example: nuclear fusion reaction “theta pinch”

S Cyclotron dee blue discharge S Cyclotron ion source red glow PRE-SHOW DEMONSTRATIONS

I7-21 SUPERCONDUCTIVITY - MAGNET LEVITATION

J2-02 KELVIN ELECTROSTATIC GENERATOR

J1-24 ELECTROSTATIC HAIR RAISING J1-25 VAN DE GRAAFF - TRAINED RABBIT

J3-21 FARADAY CAGE J3-23 FARADAY CAGE - RADIOWAVES

J5-04 MAGNETS J6-02 ELECTROMAGNET WITH JUNK J6-03 ELECTROMAGNET WITH JUNK - WITHOUT CORE J6-04 LOW POWER - HIGH FORCE ELECTROMAGNET Gaussmeter

K4-07 BICYCLE GENERATOR

K4-01 AC/DC GENERATOR K4-02 MAGNETOELECTRIC GENERATOR WITH LAMP K4-03 MAGNETOELECTRIC GENERATOR WITH BELL

K4-21 ST. LOUIS MOTOR

K4-41 MOTOR-GENERATOR PAIR One Farad Capacitor

K1-41 BARLOW'S DISC

K2-46 MAGNET LEVITATION ABOVE SPINNING DISC

J7-22 MAGNETIC DOMAINS WITH TV J7-23 MAGNETIC DOMAINS - MODEL J7-24 BARKHAUSEN EFFECT