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Electricity

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MatC
147417.  Thu Feb 15, 2007 8:50 am Reply with quote

Godalming in Surrey was the first town in the world to have electric street lighting (in 1881). Unfortunately, the lights were turned off a after a few years because they were too expensive. To mark the 125th anniversary of its pioneering move, along with “a mayoral ball with an electric theme,” Godalming claimed to be the first town in the world to install “low-energy lighting that makes it easier to see people and features as well as being environmentally friendly.”

S: Daily Telegraph, 29 Aug 06.

 
MatC
149755.  Wed Feb 21, 2007 6:04 am Reply with quote

I know we’ve talked about Nikola Tesla in the past - how could we not, when he is almost a synonym for QI - but did we ever actually do him? If not, Electricity would seem the obvious moment. Not least because of his work on what he called ELF - extremely low frequency.

 
MatC
150048.  Wed Feb 21, 2007 3:49 pm Reply with quote

This is a question to which I don’t have an answer - but I’m sure someone here will. Why does turning things on and off fix them? Why, when my computer - or many other electrical machines - goes wrong, does switching it off and then on again make it go right again?

 
Bunter
150112.  Wed Feb 21, 2007 7:27 pm Reply with quote

Quote:
Why does turning things on and off fix them? Why, when my computer - or many other electrical machines - goes wrong, does switching it off and then on again make it go right again?


Doesn't the object revert back to its pre-crash memory?

What I'd like to know is where the energy gets displaced when you delete information on your PC?

 
dr.bob
150137.  Thu Feb 22, 2007 4:56 am Reply with quote

Bunter's right. Generally switching things off and on again will reset them to their standard "start-up" state. Since most electrical items are designed to be able to work properly when they're first started (they wouldn't be much good otherwise), this usually fixes the problem.

In the case of a PC, problems are generally caused by processes that either get stuck or go mad and run away with everything. Switching the machine down will kill off these processes so that things start to work again. It's also possible to simply kill off the relevant process without shutting down the machine, but you have to know what you're doing or else you could really shag things up (though I guess you could always just switch it off if necessary).

 
MatC
150151.  Thu Feb 22, 2007 5:19 am Reply with quote

So why does it work with other machines, that don't have memories? Is it the same principle?

 
dr.bob
150175.  Thu Feb 22, 2007 5:57 am Reply with quote

Such as?

Some machines it definitely doesn't work with. The buzzer/door release mechanism on our group of flats broke at the weekend, and switching it off and on again didn't do anything for it.

 
MatC
150903.  Fri Feb 23, 2007 3:37 pm Reply with quote

“The BBC’s electricity bill has doubled from almost £6.5 million to £13 million in the last three years.”
- Morning Star, 2 Feb 07.

 
Jenny
150932.  Fri Feb 23, 2007 5:48 pm Reply with quote

That cries out for a set illuminated only by flickering candles.

 
MatC
151063.  Sat Feb 24, 2007 5:25 am Reply with quote

Oh, yes! Or miners' helmets?

 
MatC
151064.  Sat Feb 24, 2007 5:26 am Reply with quote

Except that Stephen, of course, would have some dreadfully wasteful electric gizmo going (a champagne cooler, or whatever) that he couldn't possibly - let's be reasonable - be expected to do without.

 
Molly Cule
153140.  Fri Mar 02, 2007 3:12 pm Reply with quote

The first car with an electric self-starter was called an Adam. It was manufactured by the first motorist to be convicted of speeding, Walter Arnold - he was doing 8 mph in Paddock Wood, Kent where the speed limit was 2mph. The policeman who fined him was having dinner at the time but jumped on his bike and cycled after him for 5 miles until he caught him. Arnold paid the fine of 1 shilling then went on to be the first man in Britain to make petrol-engined, electric starting motor cars like the Adam.
s I never knew that about England, Chirstopher Winn

 
eggshaped
153207.  Sat Mar 03, 2007 4:03 am Reply with quote

Link from electricity to exercise:

The California Fitness club in Hong Kong is one of the first in the world to harness the energy produced by its patrons.

Stairmaster and cross-training machines at the gym have been wired up to the building's lighting system.

It's not all that efficient though, even with all 13 machines at the Hong Kong gym in use, the energy created is only enough to power five 60-watt bulbs. It will take 82 years for the club to pay-off its $15,000 investment.

 
Frederick The Monk
154032.  Tue Mar 06, 2007 5:30 am Reply with quote

Ported across from Edison:

Why did Topsy ride the lightning?

Topsy was the Elephant that Went Bad, having killed three people at the Coney Island Zoo. Originally they were going to hang her but the SPCA thought that was a bit nasty (not to mention quite an engineering feat). At this point Edison stepped in and poor old Topsy became embroiled, and indeed emboiled, in the War of the Currents.

The 'War of the Currents' was a publicity spat between Edison, who was promoting his direct current electricity supply and Westinghouse who used an alternating current supply. The DC system was safe but could only be used in a very small area as it couldn't be carried over long distances. AC could be distributed much more easily but required a high voltage which would be dangerous if anything living came into contact with it.

In an attempt to discredit Westinghouse, Edison started making movies of the electrocution of animals to show just how dangerous AC was. When Topsy the murderous elephant came along he couldn't believe his luck. Surely if AC killed elephants then no-one would want Westinghouse's system? To make doubly sure he also commissioned the first electric chair to prove that it was also dangerous to humans and tried to introduce the word 'Westinghoused' into the English language, meaning electrocuted.

Sadly for Edison the sheer economic argument and convenience of AC won out and his DC system died a death. The only reminder today of the War of the Currents is the use of the Electric Chair in some US states. To date, over 4,000 condemned men and women have been put to death in the electric chair since 1900 (Bedau, 1997)

TOPSY'S EXECUTION

She was first fed cyanide laced carrots to calm her down (I find they help) and then 6,600 volts were put through her via copper-lined wooden sandals.

The Commercial Advertiser of New York, carried the story on Monday, January 5, 1903.

Quote:
“Topsy, the ill-tempered Coney Island elephant, was put to death in Luna Park, Coney Island, yesterday afternoon. The execution was witnessed by 1,500 or more curious persons, who went down to the island to see the end of the huge beast, to whom they had fed peanuts and cakes in summers that are gone. In order to make Topsy's execution quick and sure 460 grams of cyanide of potassium were fed to her in carrots. Then a hawser was put around her neck and one end attached to a donkey engine and the other to a post. Next wooden sandals lined with copper were attached to her feet. These electrodes were connected by copper wire with the Edison electric light plant and a current of 6,600 volts was sent through her body. The big beast died without a trumpet or a groan.”


The footage that Edison shot of the execution is a little more disturbing however and Topsy doesn't look to be having a great time to me. One should never have to witness an elephant 'riding the lightning'.

'RIDING THE LIGHTNING'
By mid-1889, when the electric chair was introduced, the term ‘electrocution’ had not yet been deemed the official term for the procedure. In fact, New York attorney Eugene Lewis suggested several alternative names, including ‘electricide’ (Penrose, 1994: 55). Thomas A. Edison also suggested names for the electric chair itself, which included ‘dynamort’, ‘electromort’, and ‘ampermort’ (ibid.).

Teh term 'Ride the Lightning' is first recorded in 1935 Jrnl. Abnormal Psychol. XXX. 364 Ride the lightning, to be electrocuted. 1965 Daily Progress (Charlottesville, Va.) 22 Mar., He pleaded for an opportunity to ‘ride the lightning’ of the electric chair. 1968 Sunday Truth (Brisbane) 15 Sept. 10/3 Four hours before I was ‘to ride the lightning’ in the chair a man came to the jail and confessed.

 
Frederick The Monk
154034.  Tue Mar 06, 2007 5:35 am Reply with quote

Question: How fast do electrons travel along a wire?

Forfeits: Speed of light

Answer: slower than a snail crawls

Notes:
The speed of electricity through a wire is a bit of a complex question. It depends on whether you are considering the rate at which electrons themselves flow along a wire or whether you are considering the rate at which an electrical signal passes along a wire.

If you define electricity as the flow of current, then electricity travels much slower than the speed of light. What you are looking for is drift velocity of electrons through a medium. The speed depends on the amount of current and certain characteristics of the medium it is propogating through. In this case, electrons themselves move quite slowly - just a few centimetres an hour. For a 1 mm diameter copper wire carrying a 10 amp current the drift velocity would be 337m per hour (or 0.3 mph). Clearly, this is not what we observe when we turn on a light switch.

However, the electric field in the wire is established at close to the speed of light (this is the signal sent from your light switch to your light bulb, from example) and electrons closest to the bulb start flowing through the bulb as soon as this field is established.

Ideally, electricity moves at the speed of light. Imagine a tube full of marbles. If you push a marble in at one end of the tube, another marble pops out the other end almost instantaneously. Even if the individual marbles are moving very slowly, the marble "wavefront" is travelling at a very high velocity.

In the real world, things are not quite so tidy. Electricity flowing through a gas, or having to work its way through electronic components such as resistors or capacitors, can be slowed to speeds of 60 to 80 percent of light speed. However, that's still fast enough that you can safely expect the light to come on as soon as you flick the switch.

 

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