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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

USA - middle bits

 

 

 

 

 

In September and October 2017 Wendy and I took another trip to the United States where we wanted to see some of the 'middle bits'.  Travel notes from earlier visits to the East coast and West Coast can also be found on this website.

For over six weeks we travelled through a dozen states and stayed for a night or more in 20 different cities, towns or locations. This involved six domestic flights for the longer legs; five car hires and many thousands of miles of driving on America's excellent National Highways and in between on many not so excellent local roads and streets.

We had decided to start in Chicago and 'head on down south' to New Orleans via: Tennessee; Georgia; Louisiana; and South Carolina. From there we would head west to: Texas; New Mexico; Arizona; Utah and Nevada; then to Los Angeles and home.  That's only a dozen states - so there are still lots of 'middle bits' left to be seen.

During the trip, disaster, in the form of three hurricanes and a mass shooting, seemed to precede us by a couple of days.

The United States is a fascinating country that has so much history, culture and language in common with us that it's extremely accessible. So these notes have turned out to be long and could easily have been much longer.

Read more ...

Fiction, Recollections & News

A Secret Agent

A crime fiction...

Chapter 1

 

 

 - news flash -

Body in River

Monday

 

The body of a man was found floating in the Iguazú river this morning by a tourist boat.  Mary (name withheld) said it was terrible. "We were just approaching the falls when the body appeared bobbing in the foam directly in front of us.  We almost ran over it.  The driver swerved and circled back and the crew pulled him in. The poor man must have fallen - or perhaps he jumped?"

The body was discovered near the Brazilian side but was taken back to Argentina. Police are investigating and have not yet released details of the man's identity...

 

Iguazú Herald

 

Everywhere we look there is falling water. Down the track to the right is a lookout to the other side of the gorge, in Brazil, where the cliff faces are covered by maybe a kilometre of falling curtains in white windswept water. Here and there the curtains hang in gaps or are pushed aside by clumps of trees and bushes, like stagehands peeking out into a theatre before the performance.  

Read more ...

Opinions and Philosophy

Population and Climate Change – An update

 

 

Climate

 

I originally wrote the paper, Issues Arising from the Greenhouse Hypothesis, in 1990 and do not see a need to revise it substantially.  Some of the science is better defined and there have been some minor changes in some of the projections; but otherwise little has changed.

In the Introduction to the 2006 update to that paper I wrote:

Climate change has wide ranging implications...  ranging from its impacts on agriculture (through drought, floods, water availability, land degradation and carbon credits) mining (by limiting markets for coal and minerals processing) manufacturing and transport (through energy costs) to property damage resulting from storms.

The issues are complex, ranging from disputes about the impact of human activities on global warming, to arguments about what should be done and the consequences of the various actions proposed.

Read more ...

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