Ch4: The age of Electrcitiy Flashcards
Leyden Jar
- > (thin) glass jar or bottle, half filled with water
- > outer surface cover in tinfoil
- > chain or wire dipped inside
Nollet performed experiments
->e.g. growing plants undercharge = 4x faster but less hardy
Caused scientific interest in electricity to swell
- > Franklin dominant figure
- > similar to pneumatic trough in this way
Views on Lightning
Prevailing: Thunder, lightening = exploding gas
->no consensus on nature of gas
Franklin theorised it was electricity, used to propose lightning rod
->religious opposition - lightning is divine wrath, you better take it
Dufay
Tried to electrify everything
- > found glas isolates the best
- > metals hold strongest charge when insulated
With electrified glass and electrified amber, they repel like but attract opposite.
- > decides there’s two kinds of electricity
1) Vitreous Electricity (Franklin replaced, +) - > rubbing glass substances
2) Resinous electricity (Franklin replaced, -) - > rubbing waxy surfaces
Franklin
Unifies electricity
Unlike Dufay, saw one electricity
- > all bodies have it in neutral state until charge via friction
- > an excess = positive, loss = negative
- > “electric per se” -> conductor
- > “non-electric” -> “non-conductor
Demonstrated contention with experiment:
- > attach wire to outer coating of jar
- > pass another wire through cork, into water
- > between terminals, suspend a cork ball
- > place jar on wax so it doesn’t leak through floor
Result Cork oscillates, “fetching fire”from inside until equilibrium is restored:
Worked on Leyden jar
- > thought charge resided in the glass - outside jar = +, inside = -
- > rubbing just transfers charge between surfaces, 1:1
Coins “ELECTRIC BATTERY” for row of Leydens joined
Galvani
ANIMAL-ELECTRICITY
- > eels give shocks
- > Galvani experimented by connecting frog legs to electric machine
- > they twitch and spasm
- > scalpel causes twitch even if machine is on, even if spark doesn’t make contact
- > spark causes twitch -> Galvani thinks he can confirm lightning is electricity
- > legs twitched when thunderclouds but also without thunderstorms…
- > realized twitching occurs whenever muscles touch two different metals, unrelated to atmospheric conditions
Galvani decides dead animals have an innate animal electricity (it is not the metal causing twitch)
- > decides animals are just fleshy Leyden jars
- > “ANIMAL-ELECTRICITY”
Volta
METAL-ELECTRICITY AND THE PILE
- > invented the battery
- > important for providing continuous current, not discharge
Inspired by Galvani
- > but Galvani was a physician, Volta is a chemist/physicist
- > does not buy “animal-electricity”
Tweaks the experiment:
- > same results when connect to nerves only, not muscles
- > saw electricity produced whenever two diff metals used
- > some metals twitch more than others
Exerimented with metals:
- > tinfoil and silver coin in mouth (one top, one bottom)
- > press together, sour taste = electrical discharge
- > taste lasts while tin and silver in contact
- > i.e. continuous flow
- > same result with silver spoon, copper wire…
Conclusion: Metals aren’t just conductors - they responsible for production
->frog legs actually demo of metallic electricity
Creates list of metal effectiveness
->more effective, the further away the metals are
Voltaic Pile
Volta realised electrical forces not only from diff metals touching - but also metal touching certain fluids
- > e.g. saliva
- > even more effective - two metals sep by fluid
Voltaic Cell:
- > make a sandwich of metal plates (silver and zinc)
- > cardboard soaked in brine between them
- > problem with brine drying out, weakening current
Solution:
->use rings of cups of brine, with strips of zinc and silver
Frictional electric discharge:
->high V, low I
Voltaic Pile:
->low V, high I
Won him praise from Napoleon and a title
The Impact of Voltaic Pile
Chemistry got a tool for:
- > tracking new elements
- > understand chemical bonds
e. g. decomposing water to H & O
Used to explode powder mines gunpowder, spark»_space; fuse
->impressive spectacle, spooky explosions at a distance
Humphry Davy
ELECTROLYSIS
Ambitious chemical experimenter with the voltaic pile
->discovered how to prepare laughing gas (NO)
With help of Pepys, made strongest pile yet
- > 60 pairs of plates
- > melting wires, igniting sheets of metal
Suspected chemical reaction was producing electricity
- > wondered - can electricity produce a reaction?
- > experimented with electrolysis
- > i.e. using electricity to produce chem change
- > previously, super strong unbreakable bonds prevented isolation and study of elements
- > e.g. nobody could break Oxygen away
Makes hyper strong 250 cell battery
->e.g. finds Potassium
Berzelius (1779-1848)
An experimenter similar to Davy
- > isolated many metals
- > gave us our modern chem notations of letters
- > put a table of weights, with O = 100
