Lec 6: Faraday, Unity of Forces Flashcards
Immanuel Kant
Kant’s Program
Very influential on positivistic view that was developed in 19th Century
->positivistic = everything has math. or scientific proof
e. g. Newton’s 3rd rule - invariance of physics
- >many thought lacked foundation
The Metaphysical Foundations of Natural Science (1786)
- > everything is a force - there is no “solid”
- > a table is just a repulsive force on our fingers
- > UNITY OF FORCE - attraction/repulsion aren’t just material properties
- > can be thermal, optical, E, B…
- > all forces are attraction and repulsion in different guises
- > then all forces are transformable into another
- > conservation of total force
Kant was a good Newtonian, but also a critic
Kant - “The Critique of Pure Reason” (1781)
- > Newton couldn’t know if atoms even exist
- > guessing their qualities is speculation on conjecture
- > we should just describe nature & its laws
- > do not offer explanation of the sub-sensible entities
Hans Christian Oersted (1777 - 1851)
The EM Effect
- > saw chemical affinity as chemical manifestation of E force
- > thought it was just the first conversions between forces
Searched for other transformations
- > at this time, link between electrostatic & voltaic forces to magnetic force was known
- > thunderstorms messed magnetic compasses
- > 1820, placed conducting wire over & // to magnetic needle
- > needle moves to right angle
- > demonstrates link - Electricity and Magnetism
- > interaction between DIFFERENT forces!
- > strange - not a central attraction/repulsion
- > I makes circular B
- > needle will go tangent to the field
Called the ElectroMagnetic effect
- > published in “Experiments on the Effects of a Current of Electricity on the Magnetic Needle”
- > a memoir to his friends in Europe
- > big news, compared to Coulomb’s idea of E & M indy
Shock, why?
- > nobody had even looked because Coulomb had conclusive looking experiments in 1780’s showing unlinked
- > Oersted only looked because he rejected imponderables, and believed in unity of force
André Marie Ampère (1775-1836)
Like most scientists, thought forces couldn’t cross interact. Shocked by Oersted
- > witnessed demonstration of EM by Arago
- > showed I can magnetize iron, and act on magnets
Devised experiments to determine I-B relationship
- > // wires attract if I same direction
- > first of 5 papers describing wires carrying currents, fundamental laws of electrodynamics
Ampere eliminated “magnetic fluids”
- > scientists could get easily controlled B fields without loadstones/bars
- > prev, loadstone was only magnetic power source
Michael Faraday - EM work?
8 months passed from Oersted’s commnications
- > tons of works done
- > Faraday went and repeated almost all of them
Faraday’s EM Rotations:
- > wire can move around a fixed magnet
- > magnet can move around a fixed wire
- > shocking, device could continue in constant motion against friction (depleting the battery)
- > the first electric motor
Drama, Davy said Faraday inspired by conversation between Davy and Wollaston.
Apparatus:
- > two vessels with mercury, each with magnet&wire
- > one fixes the magnet, one fixes the wire
Barlow
Used Faraday’s EM rotations to build Barlow’s wheel; first real motor
Michael Faraday - 1820 chemistry?
- > produced the first known compounds of chlorine and carbon (our modern ethylene)
- > oil of the Dutch chemists with chlorine in sunlight = perchlorate of carbon (C2Cl6)
- > This was the first SUBSTITUTION reaction
- > SERIOUS CHALLENGE TO DUALISTIC THEORY
Faraday - 1830 hunt for M -> E link?
What shape should an electromagnet be?
->must be strong, act powerfully on circuit
A ring, 6 inches diameter, made of 7/8 inch iron
- > wound two coils onto it, one on each half
- > one coil galvanomenter, other battery
- > became first transformer
- > Faraday only saw current when close/open ing circuit
- > concluded it was like a Leyden jar not a voltaic battery (i.e. discharge)
Noticed - iron filings on paper over magnet -> patterns
- > took as lines of forces
- > saw that when opened lines go out, when closed the collapse back in
- > the second wire cuts THROUGH their path!
Another demonstration - moved magnet over coil
- > galvanometer swings when magnet moves
- > demonstrates RELATIVE motion is needed
Faraday goes on to make the first generator (continuous electricity source)
- > set copper wheel so edges pass between poles of a magnet
- > wheel turns, gets current
