Lec 11: The New Alchemy Flashcards
Tools of the new Physical Labs?
Ruhmkorff Coil
- > induction coil - iron core, wound with layers of thick insulated wire
- > around the wire, thousands of fine insulated wire
Vacuum Cylinder Pump (Francis Hauksbee)
- > bulb of mercury
- > created a vacuum, took hours to do
Galvanic Cells (fiddling) Accumulators (constant recharing)
Galvanometers (measure I)
- > small moving coil will be deflected
- > attach a small mirror, read by oil lamp + scale
Figures in the Industrial Rev of Science?
James Watt
->Steam engine starting indy rev
Richard Trevithick
->locomotive
William Whewell
->gives the name “scientist”
William Thomson
- > very first phys lab in 840
- > pushed to specialization
Cathode Rays
Green glow emitted when:
- > glass tube with wires at opposite ends
- > remove air
- > apply high V
Goldstein argued it was rays from negative electrode striking glass
- > -‘ve electrode = cathode, hence cathode rays
- > path of rays can be altered by B
- > but E no effect
- > therefore thought rays were a wave
- > if rays were elect’d marticles, E would affect!
Varley reinterprets:
- > its collision of particles
- > since B deflects, must be carriers of electric charge
- > however, can’t explain why E unaffected
Hertz shows rays aren’t deflected by E charge metal plates
- > wrongly suggests rays can’t be charged particles
- > put metal foil in path, and glass still glowed
- > rays penetrates through foil, so must be wave
Perrin showed rays deposit negative electric charges on impact
->didn’t show the charged particles were the cathode rays themselves though, and not some coincident particles
Crookes’ Tube
AKA Cathode Ray Tube
- > string-and-sealing wax arrangement
- > examine cathode rays at diff gas pressures
- > subject them to B fields
He calls the rays the “fourth state of matter”
- > unlike solid/liquid/gas
- > did not realize, he was making X-rays
- > he thought they were electrical particles (Goldstein disagreed)
Puts Potash at the bottom
- > can heat, releasing water vapour
- > allows him to reduce the vacuum
- > make curved path get flatter
- > velocity increases as vacuum purer
B effect:
- > bar makes beam goes into a spiral
- > horseshoe bends into a curve
- > deflection consistent with -‘ve particles
Shadowgraphs
Konrad Rontgen discovers new rays, X-Rays
- > far more penetrating than cathode
- > unaffected by magnetic deflection
Process:
- > discharge of Ruhmkorff coil through Hittorf vacuum tube, covered in black cardboard, apparetus shines on discharge
- > background in solids, but had accident with Crookes’ tube
- > happened to have screen coated in fluorescent material (potassium platinocyanide) on table
- > it lit up
- > somehow, rays went through cardboard box, air, and then illuminated screen
Decides to place hand in front of screen
- > sees his bones
- > it’s a new kind of radiation - penetrates flesh, wood cardboard, foil , fabric….
- > but not stone, bone, metal anything dense
- > called it a “shadowgraph of his hand”
Progression of the X-Ray
Mass excitement
- > used for health procedures
- > within a year 1000 publications, though half of them don’t know what they’re doing
Evolves into the Fluoroscope
- > allows direct observation of object, not an image on a plate
- > can observe things as they move
- > but after Dally ded, Edison stops
Questions on Radiation
Was new, many questions.
- > Rontgen suggested it was longitudinal vibrations, not transverse vibrations of the aether
- > Thomson and the Cavendish studied
Scientists agreed:
- > rays are deflected by B field
- > produce thermal/mechanical effects on matter
- > on certain substances, produced phosphorescence
Big question: Goldstein’s aether-wave, or Crookes’ corpuscles?
And after Thomson, and then Curie’s radioactivity:
- nature and source of energy?
- how can it make things radioactive at a distance?
At least two kinds of rays
1) Detected by B field
2) Travel few inches and disappear
Thomson and the Electron
It turns out the particles in the rays are electrons. How do we know though?
Thomson experiments
- > with superior vacuum, E field will shift rays!
- > veer towards +’ve pole
- > measures beam deflection in E adn B field, finds both velocity and ratio of Q:m of particles
Thomson gives 3 hypotheses. 1&2 generally accepted, with some rewordings:
1) Cathode rays = negative charge corpuscles , 1000x smaller than Hydrogen
2) Corpuscles are constituents of atom
- >i.e. building block of the atom
3) Corpuscles are the only constituents of the atom (leaping to conclusions here)
Thomson proposes the “Plum Pudding Model”
Plum Pudding Model
Thomson’s model of the atom
->thousands of negative corpuscles, in a massless positive cloud
Henri Becquerel
X-Rays affect phosphorescent substances - but is it just X-Rays?
->phosphorescent = light emitted by a substance, not related to heat)
Can substances retain light, like sticking a poker in a fire?
- > exposed salts to the Sun
- > laid on photographic plate, wrapped in black paper to protect from ordinary light
- > one salt uranium - gave silhouette of itself in black on the negative
Thought he’d gotten X-Rays without Crookes’ tube
- > thought sunlight makes crystals emit radiation
- > however, same results occur in the dark
Conclusion: The URANIUM CRYSTALS EMIT RAYS
->but he couldn’t alter the ray properties no matter what he did chemically
Marie Curie
Inspired by her teacher Becquerel, thought rays explained by uranium atom.
->then studied thorium, also emits
Tried to explain the rays, with apparatus
- > two metal plates with +100V between them
- > sprinkle powder on lower plate, use electroscope to measure Q
- > set out to produce Uranium compounds
Sourced from PITCHBLENDE
- > pitch black variety of uranium compound
- > Curies prepared fairly pure Uranium
Problem:
- > rays of pure uranium weaker than pitchblende
- > deduces pitchblende has something stronger in it
- > in her shack, she goes through a ton of ore
- > isolates a decigram of radium - 1M stronger
- > and then Polonium
Rutherford - Theory of Atomic Transmutation
Rutherford tried to measure the penetrating power of uranium radiation
->in terms of ionization produced
Placed uranium on lower plate, covered in metal foils
->found two different emissions
After a decade, he discovers:
1) Alpha
- >little penetrating power, lots of ionization (+,- ions)
- >charged atoms of helium gas (2p+2n)
2) Beta
- >penetrating as X-Rays, very little ionizing power
- >stream of electrons
But working with Soddy, he creates daring new theory of atomic transmutation
- > introduces gamma rays
- > high energy EM radiation, undeflected by B
- > penetrate a cm of lead
Soddy then discovers “Isotopes”
Radio-Activity
Rutherford’s new hypothesis in 1903:
When there is radioactivity, there is
- > chemical change; new bodies appear
- > dissociation of single particles
- > activity proportional to mass of radioactive element, dissociating particles are atoms not molecules
- > energy liberated is 1000x than the most violent chemical rxns
Believes radioactivity is explosive disintegration of the elementary atom
- > one atom in a million explodes
- > alpha, beta, gamma ray are ejected
- > leaves a different atom behind
Then large particles can break down to smaller ones
->claims its how new matter is produced
Geiger & Rutherford
Worked out ways to count alpha particles
- “ionization by collision” gives Geiger counter
- then alpha strikes phoshorescent substance, glow is NOT UNIFORM
- > many bright poitns, flashing monetarily
- > called SCINTILLATIONS
Rutherford’s Atom
Central positive nucleus orbit by -‘ve electrons
- > almost entire mass in nucleus
- > nucleus consists of +’ve protons
- > overall charge neutral, hold atom together
- > becomes ion if electrical balance distrubed
- > X-Rays ionize air by knocking e- off atoms
Realised that protons are added/deleted constantly
->alchemy is sort of a thing, Polonium -> lead
He theorized a neutral particle would be found
- > could move freely through matter, without attract/repel by other particles
- > Chadwick found 20 years later
When smashing atoms, suspected missing matter became pure energy
- > Einstein’s special relativity nail in coffin
- > Rutherford splitting the atom first exp proof for Einstein
