Adventures with Electric Charges 
Adventures with Electric Charges
by Prof. Miller
Video Lecture 40 of 46
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Date Added: February 5, 2015

Lecture Description

A - The ELECTROPHORUS: We have in this device a remarkable scheme of things. A lucite slab is rubbed or slapped with a cat's fur. This WORK separates charges. Now we put on the lucite slab a metal plate equipped with an insulating handle. We touch the upper surface of the metal plate. This grounds this face of the plate! Row we lift the metal plate away from the lucite slab. This is now quite hard to do since the Coulomb forces are very large. But doing it requires WORK again and this energy shows itself in the availability of an electric spark. With this energy we can light a fluorescent lamp! And - a wonder to say: We can continue to take energy from this system FOREVER - which is a very long time! It is not that we have a Perpetual Motion Machine - no - never that - but rather that work is required to separate the plate from the slab -and work and energy are synonymous.

B - The Smoke Precipitator: A glass tube is fitted up with electrodes. We put some smoke in the tube. We connect the electrodes to a van de Graaff generator - a device for producing a large electric spark. Instantly the smoke disappears. The reason: the smoke is made up of charged stuff in abundance. When the van de Graaff is turned on large electric field arises between the electrodes whereupon the charged stuff migrates to the charged terminals - moving under the action of the electric field.

C - A three-vaned device has pointed ends - sharply pointed. We place it atop the sphere of a van de Graaff. Charges move to the sharp points. This accumulation of charge - which becomes very dense at sharp points - gives rise to a charge migration from the sharp points to ions in the air. These ions are abundant at all times - due to cosmic radiation. In addition - some are brought about by the intense electric field in the region of the points. The reaction forces turn the spin-wheel.

D - The Mad Professor's Head: An array of slips of paper are fitted to a stand. The system is put atop a van de Graaff. The charges move to the paper strips and because all the strips now carry the SAME charge the mutual repulsive forces drive the paper slips from each other. This can be done with the hair on your head - but be careful!

E - A candle flame is placed between two electrodes - one sharp pointed-the other a sphere. With charge from a van de Graaff it can be shown that the greatest charge density arises at sharp points. It is further seen that a flame contains ions in abundance. This brings to mind the classical report of Ben Franklin to The Royal Society wherein he recommended sharp points as lightning arrestors to protect homes and barns from "that mischievous thing called lightning".

F - We show a Dissectible Leyden Jar. This is a device made up of three parts - two conductors and an insulator. We can "store" electric charge in this thing with extraordinary results. With the inner conductor in contact with the charged sphere of a van de Graaff and the outer one grounded by hand we CHARGE the Leyden Jar - which we can call a condenser or a capacitor. Now if we connect the innermost conductor with the outermost a fat sharp spark is gotten - representing enormous energy. It is usual to say that the energy resides in the insulator which we call the dielectric.

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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