Adventures in Magnetism 
Adventures in Magnetism
by Prof. Miller
Video Lecture 41 of 46
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Date Added: February 5, 2015

Lecture Description

We find in Nature certain stuffs which are magnetic. Fe - Ni - Co are naturally magnetic. And magnetite - an iron ore - is magnetic. In fact -everything is magnetic to some degree - some things more - some less. The reason for this is clear: The primordial origin of magnetic forces lies in the motion of electrons. In some stuffs the magnetic domains are more abundant than in others.

A - How can we make a magnet: Answer: Hold a magnetizable bar - like an iron bar -in the Earth's magnetic meridian. Give it a proper "dip". Now strike it sharply with a hammer... at one end. The bar is - presto! magnetized! A wonderful thing really. We can check this by approaching a compass needle with one end of the bar just magnetized. If the needle is repel led the bar IS magnetized. Only repulsion proves this. Attraction does not! The reason is clear: A bar of magnetic stuff unmagnetized will attract a compass needle. See why?

B - How else can we make a magnet? Answer: Wrap a coil of wire around a magnetic stuff - like an iron rod say. Energize the coil with an electric current. The bar becomes polarized. It is a magnet. This results from the fact that a current-bearing conductor gives rise to a magnetic field. . .discovered by Oersted in 1820.

C - How else can we make a magnet? Stroke a bar of iron - say - with a chunk of magnetite or with another magnet. The polarity of the sample magnetized is governed by the pole last leaving the sample.

D - Problem: We magnetize a sample of stuff - say an iron rod. It has a certain "pole strength". That is to say: it is so strong. Now we break this bar just magnetized. The pieces each become a complete magnet with their own poles. Question: What is the pole strength of each piece? A very good question. HINT: We do work to break the original magnet. THIS energy must play some role somewhere.

E - Problem: We have two identical bars - absolutely identical - or so they look. One however is magnetized - the other is not. How can we determine which is the magnet without any accessories whatsoever? No strings to hang them on - no needles to try - nothing at hand. We are free however to handle both bars with utter freedom. HINT: The influence of a bar magnet is largely concentrated at the ends. Need we say more?
F - Question: Is stainless steel magnetic? Answer: No. And so we ask further: Why?

G - How can we protect a region or a thing from magnetic influence? That is - how can we insulate against magnetism? We explore this with numerous stuffs - Al - Zn - Cu - wood - lucite - and so on. And we find that magnetic insulation is best accomplished by surrounding the thing we wish to protect with a proper thickness of soft iron.

H - We explore the region around an arrangement of bar magnets by
sprinkling iron filings. The forms which come to light are enchanting to see.

Course Index

  1. The Idea of the Center of Gravity
  2. Newton's First Law of Motion: Inertia
  3. Newton's Second Law of Motion: The Elevator Problem
  4. Newton's Third Law of Motion: Momentum
  5. Energy and Momentum
  6. Concerning Falling Bodies & Projectiles
  7. The Simple Pendulum and Other Oscillating Things
  8. Adventures with Bernoulli: Bernoulli's Principle
  9. Soap Bubbles and Soap Films
  10. Atmospheric Pressure
  11. Centrifugal Force and Other Strange Matters
  12. The Strange Behavior of Rolling Things
  13. Archimedes' Principle
  14. Pascal's Principle: The Properties of Liquids
  15. Levers, Inclines Planes, Geared-wheels and Other Machines
  16. The Ideas of Heat and Temperature
  17. Thermometric Properties and Processes
  18. How to Produce Heat Energy
  19. Thermal Expansion of Stuff: Solids
  20. Thermal Expansion of Stuff: Gases & Liquids
  21. The Strange Thermal Behavior of Ice and Water
  22. Heat Energy Transfer by Conduction
  23. Heat Energy Transfer by Convection
  24. Heat Energy Transfer by Radiation
  25. Evaporation, Boiling, Freezing: A Dramatic Adventure
  26. Miscellaneous Adventures in Heat
  27. The Drama in Real Cold Stuff: Liquid Nitrogen
  28. The Physics of Toys: Mechanical
  29. The Physics of Toys: Acoustic and Thermal
  30. Waves: Kinds of Properties
  31. Sound Waves: Sources of Sound & Pitch and Frequency
  32. Vibrating Bars and Strings: The Phenomenon of Beats
  33. Resonance: Forced Vibrations
  34. Sounding Pipes
  35. Vibrating Rods and Plates
  36. Miscellaneous Adventures in Sound
  37. Electrostatic Phenomena: Foundations of Electricity
  38. Electrostatic Toys, Part 1
  39. Electrostatic Toys, Part 2
  40. Adventures with Electric Charges
  41. Adventures in Magnetism
  42. Ways to "Produce" Electricity
  43. Properties and Effects of Electric Currents
  44. Adventures in Electromagnetism
  45. Further Adventures in Electromagnetism
  46. Miscellaneous and Wondrous Things in E&M

Course Description

Demonstrations in Physics was an educational science series produced in Australia by ABC Television in 1969. The series was hosted by American scientist Julius Sumner Miller, who demonstrated experiments involving various disciplines in the world of physics. The series was also released in the United States under the title Science Demonstrations.

This program was a series of 45 shows (approximately 15 minutes each) on various topics in physics, organized into 3 units: Mechanics; Heat and Temperature / Toys; and Waves and Sound / Electricity and Magnetism.


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