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Electrical Question in 'Pub Quiz'

Discussion in 'Electrics UK' started by CAWORK, 30 Jun 2020.

  1. SUNRAY

    SUNRAY

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    .
     
    Last edited: 1 Jul 2020
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  3. SUNRAY

    SUNRAY

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    I thought I'd get round that by asking what are the FOUR primary colours, the arguement was even worse until I shone red, green and blue lights on the ceiling
     
  4. SUNRAY

    SUNRAY

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    Ah yes but...

    I've worked on 3 phase with phase colours of: red, green, blue which then changed to red, white, blue and then to red, yellow, blue. So for old timers green, white or blue were alien colours for neutral.

    I've also worked on old single phase of orange [or red] and green. and it was only in the last 5 years that I sorted out some of our old [disused] cables of red/green twisted [without second layer] rubber which I think I remember Dad buying in woolworths.

    On Holiday in Madeira I noted the T&E was brown & blue and bare earth sheathed red, chatting to the Hotels maintenance guy it seemed there was a great reluctance to change to green/yellow.
     
  5. JohnW2

    JohnW2

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    NO. NOT Anti- / Post- Meridian [a line of longitude] BUT Ante- / Post- Meridiem [Latin for 'Middle of Day' {meri diem'}, taken by some to mean when the sun is at it highest].

    Kind Regards, John
     
    Last edited: 2 Jul 2020
  6. ericmark

    ericmark

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    This is why I blame the railways, before the railway and time tables each town could have a slightly different time likely set with a sun dial which would likely be correct.
     
  7. FrodoOne

    FrodoOne

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    Concerning sun-dials, have you ever considered why "clockwise" is the direction which it is?
    It is because that is the direction the shadow of the gnomon on the Sun-dial moves - in the Northern Hemisphere - where both Sun-dials and clocks were invented.
     
  8. ericmark

    ericmark

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    So do sun dials move anti clock wise in southern hemisphere? That would mean they would not work on in the tropics as they were reverse direction summer and winter, but I think they do work. Like the direction of water down a plug hole, it does not really change.

    But with a sun dial they show true time, so if where you live midday is at 12:14 UTC then that is when a sun dial should show 12:00. The easy method is to use the unified time constant UTC it was called GMT until the observatory was moved, but UTC is used world wide.

    But is it 24 hours or 0 hours at midnight? Can we have 24 hours as at 1 minute past it is 00:01? So if there is no 24 hours on a 24 hour clock why is it called a 24 hour clock? and if there is no 24 hours on a 24 hour clock is there a ΒΌ past 12 on a 12 hour clock?

    Anyway time a got my first meal of the day, breaking my over night fast, so called Breakfast, where does Brunch come from?
     
  9. DetlefSchmitz

    DetlefSchmitz

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    Seriously? Picture a globe in front of you with a pin sticking upwards on the top, and the globe is rotaing anticlockwise (because that defines the north pole as being on top). Now image a lamp off to the side (the sun). Now imagine which way round the shadow will rotate around the pin. (Obviously clockwise).
    Now picture the pin being move to the bottom. Relative to the 'ground', which way round does the shadow move now?
    At the equator the shadow simply moves back and forth in a straight line.
     
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  11. JohnW2

    JohnW2

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    Inevitably.
    They will 'work', at least in some senses, even at the equator. Although the shadow will then always follow a straight line East-West path (rather than 'rotate'), the length of the shadow will vary with the time of day (being of zero length when the sun is directly overhead, at 'midday'). The further you get from the equator (even within the tropics), the more of a 'rotational' component of the shadow path will appear, but I'm not sure how far one has to get from the equator before the angle of rotation (rather than just the length of the shadow) become 'useable'.

    By the way, returning to your comments about trains and timetables, I think that mechanical clocks were developed, largely as an aid to maritime navigation, centuries before trains - so you probably should be 'blaming' ships, rather than trains :)

    Kind Regards, John
     
  12. EFLImpudence

    EFLImpudence

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    The gnomon (new word learned) has to be parallel to the Earth's axis, i.e. tilted at the location's latitude toward the relevant pole.

    Therefore at the equator it has to be horizontal with a curved scale beneath (otherwise the nearer sunrise and sunset the shadow will be a long way away).
     
  13. Harry Bloomfield

    Harry Bloomfield

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    Harrison is to blame :)
     
  14. EFLImpudence

    EFLImpudence

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    There was no need for ships to have the same time in Penzance and London.

    All they needed was an accurate clock to tell them the time in London, then they could work out there longitude
     
  15. JohnW2

    JohnW2

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    I don't think that is conceptually essential - one can 'tell the time' from the shadow of a simple vertical pin.
    Indeed - I presume you mean 'curved' in the up/down plane - i.e. one would have to have the gnomon (or pin) in the middle of something like a soup bowl, in order to avoid those very long shadows early and late in the day.

    Kind Regards, John
     
  16. JohnW2

    JohnW2

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    All true - but I thought (maybe wrongly) that eric was blaming train timetables for the development of timepieces!

    Kind Regards, John
     
  17. EFLImpudence

    EFLImpudence

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    That would vary throughout the year except at midday.

    Yes but just a part of the soup bowl.

    upload_2020-7-2_14-31-22.png
     
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