1

Technology / Re: Are cellular telephone towers safe to install in schools?

« on: 17/09/2013 12:23:59 »

Prof Moulder of The Medical College of Wisconsin is possibly the World's number one expert on the subject.   He concludes mobiles are dangerous . .. people have accidents when driving.    But I wonder how many lives have been saved when folks can get though to the emergency services quickly??

http://www.mcw.edu/radiationoncology/faculty/johnmoulder.htm

There are some really loony folk out there who have illogical fears and there are sharks who prey on them.    BBC did (not too scientific) experiment.   It filled an hotel with folks some of whom claim to be electro-sensitive.  They put an temporary mobile base in the car park.  One lad felt so ill he had to go home.  At that point the base hadn't been powered.   

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Technology / Re: What type of transformer are my suppose to draw?

« on: 08/09/2013 15:02:11 »

Transformers are actual quite complex to analyse as there are copper and iron losses as well as magnetic effects like hysteresis and saturation.  If you want 24 V output from a 240 V supply you will need something like an 8 to 1 ratio as the output voltage will drop when the transformer is loaded.   Modern power supplies these days (Switch-mode)  (TVs, computers, all sorts of thing) are often far more complicated than simple transformers.  They usually chop up the incoming mains at a high frequency which allows a much smaller more efficient transformer to be used.  The output voltage  is adjusted by changing the on-off period of the switching and a feedback system can stabilise the output voltage so it doesn't vary (much) with loading.   A simple transformer either with AC out or rectified to DC is poor as regards the voltage dropping as the load is increased.   They can be made stable (DC out) by using a 'linear regulator'. 

3

Physics, Astronomy & Cosmology / Re: Space junk

« on: 07/09/2013 14:49:35 »

If there are 20,000 objects over 5cm in orbit and given that the UK has an area 1/2000 of the Earth there will be just 10 objects over the UK at a moment in time and given that these will be at different heights the chance of two objects colliding must be very small.   

4

Chemistry / Is brass plating possible?

« on: 06/09/2013 20:15:24 »

Copper. Zinc, Silver, God, Chrome etc...elements.. Plating seems straightforward but brass is an alloy??

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Technology / Re: The early warning radar system

« on: 06/09/2013 19:13:09 »

If you do go to Duxford visit the ham radio station and say you are interested in WW2 radio and radar and you may be taken to a hut full of old radio/radar equipment not normally shown to the public.   

http://www.duxfordradiosociety.org/

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Technology / Re: The early warning radar system

« on: 06/09/2013 19:06:55 »

I went to the Liverpool War Museum...   http://www.liverpoolwarmuseum.co.uk/  ... and sadly I was the only visitor at the time.    But maybe Duxford would be the place as it gets thousands of visitors.     The book Secret War by Brian Johnston is a MUST if you interested in WW2 Radar, knickebien, Enigma, V1s and V2s and other technologies...     ISBN 0-09-920790-7

http://www1.dragonet.es/users/markbcki/johnson.htm

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Technology / Re: What percentage of eneergy is used to convert a gallon of gas to electrical ener

« on: 05/09/2013 00:03:43 »

Slightly meaningless calculation as calorific value is a notional figure.  It comes down to economics.  If fuel A has a low calorific value and cheap it may make more sense to it rather than use fuel B which has much higher calorific value but a lot more expensive.   

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Technology / Re: The early warning radar system

« on: 04/09/2013 23:59:20 »

Have to say it would probably have a limited interest by the public and wouldn't be worth the cost...sadly.   

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Technology / Re: Are cellular telephone towers safe to install in schools?

« on: 04/09/2013 23:50:14 »

If there is any risk (no proof  after many years of use now all over the World) it will be from the phone next to the head.  The power/sq metre from a base station even a very close one is very low.  As many phones radiate less power if they are receiving a strong signal (less is needed if the base is close) siting a base station near a school could the best thing you could do.

10

Technology / If every roof of every building was made of solar panels how much electricity?

« on: 07/04/2011 17:14:15 »

The UK - France interconnector is DC.   In any case the UK is not phased locked to France.  They use lots of IGBT devices.

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Technology / If every roof of every building was made of solar panels how much electricity?

« on: 05/04/2011 10:24:52 »

However you look at it the financial return is very poor even negative.  Solar must be the most expensive source of elec we have.  

If you want to argue about saving the planet that is another matter but even there the picture is not clear cut. 

But why should the tax payer who maybe like me thinks solar is a waste of time subsidise it?

Even the much more financially viable nuclear is essentially a nationalised business. 

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Technology / If every roof of every building was made of solar panels how much electricity?

« on: 05/04/2011 10:22:42 »

However you look at it the financial return is very poor even negative.  Solar must be the most expensive source of elec we have.   

If you want to argue about saving the planet that is another matter but even there the picture is not clear cut. 

But why should the tax payer who maybe like me thinks solar is a waste of time subsidise it?

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Technology / If every roof of every building was made of solar panels how much electricity?

« on: 04/04/2011 21:34:43 »

The £11,000 was for a domestic system..maybe of the order of 16 sq metres.  The man who had bought the system kept saying his elec was free???   Yeah right..having forked out 11 Grand and having battery replacement and other costs to come?

The point is that most of the 40p comes from tax payers.
That was the central point of the BBC item.

I suspect most of these systems cannot supply heavy loads like cookers, showers, kettles, heaters, washing machines (cold fill)  particularly when you use 2 or 3 of these on at once and you have to rely on the mains for those.

14

Technology / If every roof of every building was made of solar panels how much electricity?

« on: 04/04/2011 20:16:22 »

Solar was discussed on Radio 4 today with the usual pro / anti representative.   The feed in tarrif (FIT) is a ridiculous 40 p per kWh which is around 3 to 4 times more than the going domestic rate and maybe 8 - 10 times the wholesale price (from a gas powered station)... = A massive subsidy.   

8 kWh is only about £1 worth of elec and on the Radio 4 prog they interviewed a bloke who had paid £11,000 for such a system.   

You could end up with the farcical situation of exporting all your solar elec for 40p a kwH and use elec for your own use via a cable from your neighbour at 12p a kWh. Even then payback would be about 11 years.

15

Physics, Astronomy & Cosmology / Would my GPS device work on the moon?

« on: 02/04/2011 20:59:24 »

I meant even if they fired similar power towards the Moon the signals would be 400 times weaker.  If you knew what power was going towards the Moon (by accident) you could work out what size of receiving dish was required. The dish may be so large that the beamwidth might be a tiny fraction of a degree and may have to track the satellites and possibly may have trouble picking up the required 3.  No air and therefore no wind would make it possible to construct huge dishes.

My pal bounces 144 MHz signals off the Moon.

This Swiss bloke can hear his own echos..  Probably 1296 MHz which is not too far from GPS frequencies. 

 

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Physics, Astronomy & Cosmology / Would my GPS device work on the moon?

« on: 02/04/2011 20:28:37 »

The signals will be directed towards Earth and the distance to the Moon is 20 times further and just on that basis the signals would be 26 dB weaker (400 times less power).  You would need a fair sized parabolic dish.. 3 metre or more.

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Technology / If every roof of every building was made of solar panels how much electricity?

« on: 01/04/2011 10:34:44 »

I am not predicting a 5 fold decrease in solar prices.  I am saying that is what you would need (at least).  Given poor economic conditions in many countries subsidies are likley to be reduced or removed.  This will kill demand and I think solar has no future really.  Similarly susidies for electric vehicles are likely to go and given the high cost of these vehicles they have no future either.

There is no rapid improvement in the technology on the horizon unless there a quantum leap breakthrough all of a sudden....unlikely.

18

Chemistry / Which boils faster, hot or cold water?

« on: 31/03/2011 17:21:26 »

Hot of course.  The temp is already high and you need less energy to raise it further.

19

Technology / Can a bike power a washing machine?

« on: 31/03/2011 16:57:47 »

You may be able to spin the drum but for how long?  It would not be possible to heat the water.  Most modern machines are cold fill.  Most of the energy is used heating the water. 

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Technology / If every roof of every building was made of solar panels how much electricity?

« on: 31/03/2011 16:53:01 »

You could say that if every domestic UK roof was covered that the equiv of about 8+ million homes could be supplied out of 25....Not that it would be possible to supply the 8 million 100% of the time.

Even if the panels remained as good as on the first day and no batteries etc had to be replaced the payback time is of the order of 40++ years...  In practice it means never as they will not remain as on day one and batteries certainly will have to be replaced several times in 40++ years. 

You can spend as much as  £20,000 and save as little as £200 a year = 100 years.  No sense at all economically.  Again no replacement costs considered.   

You would need a 5+ fold increase in elec prices or a 5+ fold decrease in the cost of panels.   Panels may drop in price but the reduction of subsidies in the UK and other countries will kill demand and economies of scale can't kick in.  Batteries are actually going up steeply in price.  I used to buy small lead acid at £5 a go.  Now they are £13!