Properties and Effects of Electric Currents 
Properties and Effects of Electric Currents
by Prof. Miller
Video Lecture 43 of 46
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Date Added: February 5, 2015

Lecture Description

A - The Oersted Frame: In 1820 Hans Christian Oersted - a Dane -
made an observation that stirred an avalanche in physical thought. He discovered that a current-bearing conductor gives rise to a magnetic field. We show this classic experiment. Faraday - an Englishman - heard of this great adventure and made a note in his notebook: "Make magnetism produce electricity". In 1831 Faraday did just this with his famous discovery of electromagnetic induction.

B - Metals are good electrical conductors - this we know. But how about liquids and solutions? We show a solution of copper sulphate with two lead electrodes. We "drive" a current through this solution from a storage battery and soon we see a marvelous thing: One of the lead plates has some COPPER ON IT. We thus show the conductivity in an electrolyte and the deposition of copper by electrolysis. This is copper plating.

C - How about conductivity in a "hot dog"? Sure enough - we impale a "cold" dog on two spikes - connect the system to the house line -110 volts AC - and we cook the dog! The conductivity is possible because of the salt in the meat which makes it a good conductor.

D - We connect a Cu wire to a dry-cell in a circular loop and present the wire to some iron filings. The filings gather tightly at the wire. Is the wire magnetized? No. It is not magnetized but the current-bearing wire produces a magnetic field which is strongest nearby the wire.

E - If two adjacent conductors carry a current the conductors may be pushed apart or pushed together depending on the direction of the current in them. So we suggest a demonstration using a coil known as Roget's Spiral. We avoid doing this experiment because it leads to the vaporization of mercury - which is very bad to breathe!

F - The Electromagnetic Gun: A coil of wire of HEAVY wire and few turns — this makes its Ohmic resistance low - is wound on an aluminum tube. In the tube resides an iron bar. We make connection for an instant to a 6-volt battery. The coil - now carrying a current -magnetizes the bar - draws the bar IN - AND - if we now open the circuit at the right instant the bar keeps going as a projectile. As can be seen - if the circuit is not closed and opened at critical times the weapon will not work!

G - We "short" a 6-volt storage battery by putting a Cu wire across its terminals. The current drawn momentarily may be as high as several hundred amperes.The heat developed burns the wire. What really happens is this: The wire is evaporated!

So - in these adventures - we see that an electric current can produce mechanical effects - magnetic effects - heating effects - chemical effects - optical effects - and so on. And we must not lose sight of Oersted and Faraday and scores of others whose genius made it all possible.

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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