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The electrically literate may find this somewhat simplified article redundant; or possibly amusing. They should check out Wikipedia for any gaps in their knowledge.

But I hope this will help those for whom Wikipedia is a bit too complicated and/or detailed.

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All cartoons from The New Yorker - 1925 to 2004

 

 

Think of water in a hosepipe

 

Electricity is a means of transporting energy from a source, like the wind, to a device you use to exploit that energy, like your electric toothbrush.

The usual way of explaining electricity is to use the simile of the flow of water in a pipe (a current of water).  We are all familiar with a hose pipe.  Its pressure is analogous to the voltage; and the flow of water is analogous to the current. 

 

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The author - almost two - learning about currents and voltage

 

The work that can be done in an hour, for example if you use the jet to spin a bicycle wheel or push leaves along a path, is the pressure (like Volts) times the current (like Amps) for an hour. 

You won’t be able to squirt the water from your hose far if there is no pressure or if there is no water.  You need both.  If the pressure falls the water ceases to flow.

It’s the same with a stream (current) of electricity making its way down a conductor; for example a wire. The electrical force acting on an electrical current provides the power to do work.

Most quantities in modern physics are named after an early natural philosopher or inventor.  If we had let tradition do it, each would probably be related by some strange number, like the number of feet in a mile; or pounds in a ton.  But most new physical values use the decimal system (the rationalised MKS or SI units: meter, kilogram, second).

A Watt is a measure of Power; the instantaneous capacity to do work; named after James Watt. 

Under this system we define one Watt as equal to one Volt (electrical  force) multiplied by one Ampere (current); or Amp for short.  Read More...

Using this simple relationship you can easily calculate that 1000 Watts of power (one kilowatt) can be carried by a current of 4.17 amps at 240 volts (240 x 4.17 = 1000)

But the same power requires only 0.002 amps at 500,000 volts (0.002 x 500,000 = 1000).  So when you turn on an electric kettle or toaster it will draw around 4 amps in your home at 240V but only 0.002 amps in the very high voltage grid to bring it from the generator in the power station.

Power exerted for a period of time is called Energy.  Physicists measure energy in Joules (1 J= 1Watt acting for 1 second).  But to get to a smaller working number electricity companies like to measure energy in kilowatt hours (1 kWh =  3,600 kJ = a thousand Watts acting for the seconds in one hour) 

When your bill comes, you get charged for the Energy, the number of kWh* you used, not Power (kW).

 

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*Terminology:  1000 Wh = 1 killowatt hour (kWh); 1000 kWh=1 megawatt hour (MWh); 1000 MWh = 1 gigawat hour (GWH), 1000 GWH = 1 terawatt hour (TWh).

 


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Travel

Cambodia and Vietnam

 

 

 In April 2010 we travelled to the previous French territories of Cambodia and Vietnam: ‘French Indochina’, as they had been called when I started school; until 1954. Since then many things have changed.  But of course, this has been a region of change for tens of thousands of years. Our trip ‘filled in’ areas of the map between our previous trips to India and China and did not disappoint.  There is certainly a sense in which Indochina is a blend of China and India; with differences tangential to both. Both have recovered from recent conflicts of which there is still evidence everywhere, like the smell of gunpowder after fireworks.

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Fiction, Recollections & News

A Womens' view

 

Introduction

 

The following article presents a report by Jordan Baker, as part of her history assignment when she was in year 10 at North Sydney Girls’ High School.   For this assignment she interviewed her mother, grandmother and great-grandmother about their lives as girls; and the changes they had experienced; particularly in respect of the freedoms they were allowed.

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Opinions and Philosophy

The Transit of Venus

 

 

On Wednesday 6th June, 2012 in Eastern Australia and New Zealand (as well Pacific islands across to Alaska) Venus was seen to pass between the Earth and the Sun; appearing as a small circular spot crossing the sun’s disc; for around six and a half hours.

This is a very rare astronomical event that has been the cause of great change to our world.

This is not because, as the astrologers would have it, that human events are governed or predicted by the disposition of the stars or planets.  It is because the event has served to significantly advance scientific knowledge and our understanding of the Universe.

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