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Hot wires

 

Pushing a current through a conductor requires energy.  The difficulty in doing this is called resistance; and is measured in Ohms.  For each Ohm of resistance an electromotive force of 1 Volt is required to cause a current of one Amp to flow.  In other words Resistance = Voltage (drop across the conductor) divided by the current (Amps) in the conductor.  This is called Ohms law and is obvious, a priori, from the definitions of these quantities.

The important things to know about conductors are that: resistance varies depending on the material that the conductor is made from; and the electrical energy used to overcome resistance becomes heat. Read More...

Electrical conductors get hot depending on the current flow; and the heat generated goes up exponentially as the current increases in a wire.

Suppose the lead to a power board in your kitchen is carrying 2 amps and consuming 5 Watts per metre as heat.  This is so small you don’t even notice the lead getting warm. If you add a few more appliances taking the total to 10 amps the heat in the lead will jump, not to 25 watts per metre as you might expect (5x5), but all the way up to 125 watts per metre; at which point it will probably burst into flames. This is why commercial power boards have a big safety margin with wires around twice as heavy as those in this example; so there is only moderate heating even at 15 amps.

Resistance falls as conductors get fatter, in proportion to cross-sectional area. This is obvious because two identical conductors (or water pipes) side-by-side carry twice the current of one.

You may have noticed that the cord to some high current appliances, like heaters, kettles and vacuum cleaners, gets warm.  To avoid heating the wires in your house too much and possibly burning it down, properly installed wiring has current ratings well above a safe limit; electricians are careful that all strands of a cable are terminated; and the current is limited by fuses and other kinds of current breakers. 

 

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We often want some wires in home appliances to get hot:  electric heaters, kettles, toasters, and so on work on this principle; an incandescent light bulb generates so much heat that the filament glows white hot; a fuse wire melts if the current gets above a certain limit.

But unless you want a bit of extra warmth, heating wiring in buildings is wasteful and a fire risk.  It is particularly wasteful in the street or in wires running for miles in the country.  Many millions of kilowatt hours of electricity can be lost heating the countryside.

The actual losses are equivalent to approximately 10 percent of the total electricity transported between power stations and market customers.  In long links and in those carrying high currents, from time to time, the losses can be much higher than this.

 

 

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Travel

Burma (Myanmar)

 

 

This is a fascinating country in all sorts of ways and seems to be most popular with European and Japanese tourists, some Australians of course, but they are everywhere.

Since childhood Burma has been a romantic and exotic place for me.  It was impossible to grow up in the Australia of the 1950’s and not be familiar with that great Australian bass-baritone Peter Dawson’s rendition of Rudyard Kipling’s 'On the Road to Mandalay' recorded two decades or so earlier:  

Come you back to Mandalay
Where the old flotilla lay
Can't you hear their paddles chunking
From Rangoon to Mandalay

On the road to Mandalay
Where the flying fishes play
And the Dawn comes up like thunder
out of China 'cross the bay

The song went Worldwide in 1958 when Frank Sinatra covered it with a jazz orchestration, and ‘a Burma girl’ got changed to ‘a Burma broad’; ‘a man’ to ‘a cat’; and ‘temple bells’ to ‘crazy bells’.  

Read more ...

Fiction, Recollections & News

Recollections of 1963

 

A Pivotal Year

It appears that the latest offering from Andrew Lloyd Webber: Stephen Ward, the Musical, has crashed and burned after four months in London.

On hearing this I was reminded of 1963,  the year I completed High School and matriculated to University;  the year Bob Dylan became big; and Beatle Mania began. 

The year had started with a mystery the Bogle-Chandler deaths in Lane Cove National Park in Sydney that confounded Australia. Then came Buddhist immolations and a CIA supported coup and regime change in South Vietnam that was the beginning of the end for the US effort. 

Suddenly the Great Train Robbery in Britain was headline news there and in Australia. One of the ringleaders, Ronnie Biggs was subsequently found in Australia but stayed one step of the authorities for many years.

The 'Space Race' was underway with the USSR holding their lead by putting the first female Cosmonaut into obit. The US was riven with inter-racial hostility and rioting.  But the first nuclear test ban treaties were signed and Vatican 2 made early progress, the reforming Pope John 23 unfortunately dying mid year.

Towards year's end, on the 22nd of November, came the Kennedy assassination, the same day the terminally ill Aldus Huxley elected to put an end to it.

But for sex and scandal that year the Profumo affair was unrivalled.

Read more ...

Opinions and Philosophy

Carbon Footprints

 

 

Energy Solutions

 

Most informed commentators agree that Australia needs a better mix of energy sources.  We are too dependent on fossil fuel.  This results in a very high rate of carbon dioxide production per capita; and this has international and domestic implications in the context of concerns about climate change.

Read more ...

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