poohbear 1,360 Posted February 6, 2015 Report Share Posted February 6, 2015 Trees are unpredictable, they don't always go where you want them to, sometimes they can snap and literally smack you in the head...I'm very careful when felling trees!!!! Dead trees are widow makers.. Enjoy... Quote Link to post Share on other sites
Robbie 39 Posted February 6, 2015 Report Share Posted February 6, 2015 #49 Catfan He looks like he could be quite competitive on a quote, can you get his number? I have got some ridge tiles need re-bedding on my 3 storey property and a couple of fully mature oak trees felling?. 2 Quote Link to post Share on other sites
catfan 14,793 Posted February 6, 2015 Report Share Posted February 6, 2015 Only if you have a conservertory he could work off ! 1 Quote Link to post Share on other sites
tomlinson 879 Posted February 6, 2015 Report Share Posted February 6, 2015 Dr Johnson described my DIY. 'Like a dog walking on its hind legs, it is not done well, but we are surprised it is done at all'. Quote Link to post Share on other sites
StephenFord 866 Posted February 6, 2015 Report Share Posted February 6, 2015 Hi Tomlinson - re#54 - at the risk of being highly politically incorrect, I believe that quote of Dr Johnson referred to ladies preaching (at a time when the thought of a lady vicar, let alone bishop, was completely unthinkable). Quote Link to post Share on other sites
The Engineer 614 Posted February 6, 2015 Report Share Posted February 6, 2015 My take on that electron and hole moving around stuff: When electricity was discovered, it was generated by 'cells' (put more than one cell together and you get a battery). They decided that one end of the cell was positive and the other negative (still holds today with the + and - markings) and that the electrical current flowed from positive to negative. All well and good until someone later discovered that electrical current is actually electrons moving from the negative of the cell/battery, round the circuit to the positive. Trouble was that the convention was well established by then and it wasn't practicable to try to change it. If needed for clarity, we stick the word 'conventional' in front of 'current flow' to mean positive to negative, but generally we forget the detail and just assume current flows positive to negative. That's the way all circuit diagrams are drawn and the way all test gear is used. ... and those holes? The reason why electrons move is that there are vacant spaces ('holes') at the other end of the circuit for them to slot into. We can therefore pretend it's the holes moving positive to negative instead of the electrons moving negative to positive. That allows us to say that conventional current is the movement of holes. 1 Quote Link to post Share on other sites
colly0410 1,181 Posted February 7, 2015 Report Share Posted February 7, 2015 If you say electrons move into vacant holes then that would make sense, but on the army advanced signals course they said "holes flowed in the opposite direction to electrons" as John says "how can holes flow through solids?" If they said "holes seemed to flow in the opposite direction to electrons but they don't really" that would have made more sense (well it would have to me anyway). But of course on the exam you had to say what they wanted you to say, or you'd fail.. Quote Link to post Share on other sites
Bubblewrap 3,815 Posted February 7, 2015 Report Share Posted February 7, 2015 #48 NO! he's just plain mad Quote Link to post Share on other sites
Bilbraborn 1,594 Posted February 8, 2015 Report Share Posted February 8, 2015 I just leave it to the experts. Quote Link to post Share on other sites
plantfit 7,597 Posted February 8, 2015 Report Share Posted February 8, 2015 Post Number 48, would that be a 110volt Kango breaker? Rog Quote Link to post Share on other sites
The Engineer 614 Posted February 14, 2015 Report Share Posted February 14, 2015 If you say electrons move into vacant holes then that would make sense, but on the army advanced signals course they said "holes flowed in the opposite direction to electrons" as John says "how can holes flow through solids?" If they said "holes seemed to flow in the opposite direction to electrons but they don't really" that would have made more sense (well it would have to me anyway). But of course on the exam you had to say what they wanted you to say, or you'd fail.. Let's assume a theoretical wire is made from three copper atoms. Copper is good as its electrons are easily detached (that makes it a good conductor). Each copper atom has 29 positive protons and 29 negative electrons. Here’s the wire before we connect the battery: Atom 1 has 29+ and 29- (balanced) Atom 2 has 29+ and 29- (balanced) Atom 3 has 29+ and 29- (balanced) We switch on and the battery (+) takes an electron from Atom 1 Atom 1 has 29+ and 28- and so has a positive hole Atom 2 has 29+ and 29- (balanced) Atom 3 has 29+ and 29- (balanced) Atom 1 takes an electron from Atom 2 Atom 1 has 29+ and 29- (balanced) Atom 2 has 29+ and 28- and so has a positive hole Atom 3 has 29+ and 29- (balanced) Atom 2 takes an electron from Atom 3 Atom 1 has 29+ and 29- (balanced) Atom 2 has 29+ and 29- (balanced) Atom 3 has 29+ and 28- and so has a positive hole Atom 3 gets an electron from the battery (-) to fill the hole; back to square one, ready for another round of 'pass the electron' As you see, the hole has moved from Atom 1 to Atom 2 to Atom 3. Electrons have gone the other way. Nothing is passing through solids. 1 Quote Link to post Share on other sites
Bubblewrap 3,815 Posted February 14, 2015 Report Share Posted February 14, 2015 ? It's all Greek to me. 2 Quote Link to post Share on other sites
Michael Booth 7,364 Posted February 14, 2015 Report Share Posted February 14, 2015 I'm sure you must have seen the hole move between the Atoms, Bubblewrap. 1 Quote Link to post Share on other sites
Bubblewrap 3,815 Posted February 14, 2015 Report Share Posted February 14, 2015 The only hole I usually see is the hole in my wallet when I go down the pub. Quote Link to post Share on other sites
Bubblewrap 3,815 Posted February 14, 2015 Report Share Posted February 14, 2015 Is #61 a Euclidean algorithm? http://en.wikipedia.org/wiki/Euclidean_algorithm Quote Link to post Share on other sites
TBI 2,351 Posted February 14, 2015 Report Share Posted February 14, 2015 Let's assume a theoretical wire is made from three copper atoms. Copper is good as its electrons are easily detached (that makes it a good conductor). Each copper atom has 29 positive protons and 29 negative electrons. Here’s the wire before we connect the battery: Atom 1 has 29+ and 29- (balanced) Atom 2 has 29+ and 29- (balanced) Atom 3 has 29+ and 29- (balanced) We switch on and the battery (+) takes an electron from Atom 1 Atom 1 has 29+ and 28- and so has a positive hole Atom 2 has 29+ and 29- (balanced) Atom 3 has 29+ and 29- (balanced) Atom 1 takes an electron from Atom 2 Atom 1 has 29+ and 29- (balanced) Atom 2 has 29+ and 28- and so has a positive hole Atom 3 has 29+ and 29- (balanced) Atom 2 takes an electron from Atom 3 Atom 1 has 29+ and 29- (balanced) Atom 2 has 29+ and 29- (balanced) Atom 3 has 29+ and 28- and so has a positive hole Atom 3 gets an electron from the battery (-) to fill the hole; back to square one, ready for another round of 'pass the electron' As you see, the hole has moved from Atom 1 to Atom 2 to Atom 3. Electrons have gone the other way. Nothing is passing through solids. Simples, innit? Quote Link to post Share on other sites
Bubblewrap 3,815 Posted February 14, 2015 Report Share Posted February 14, 2015 So that's how they work out my house insurance premiums Quote Link to post Share on other sites
The Engineer 614 Posted February 14, 2015 Report Share Posted February 14, 2015 ? It's all Greek to me. Well spotted ; Atom being Greek for that which can not be split ('a' means not and 'tom' means cut). Of course that name was chosen many centuries before Rutherford split the atom. Quote Link to post Share on other sites
Michael Booth 7,364 Posted February 15, 2015 Report Share Posted February 15, 2015 I think it's time for bed. Quote Link to post Share on other sites
TBI 2,351 Posted February 15, 2015 Report Share Posted February 15, 2015 So that's how they work out my house insurance premiums Pay attention Bubblewrap, that's actuarial not atomic. Quote Link to post Share on other sites
Bubblewrap 3,815 Posted February 15, 2015 Report Share Posted February 15, 2015 He went out & he's never been at om since, (sorry about that one) Quote Link to post Share on other sites
colly0410 1,181 Posted February 15, 2015 Report Share Posted February 15, 2015 Hmm, I suppose a hole is just a missing electron, a sort of not-electron (anti-electron? or is that a positron?) If you consider an electron as a physical thing (OK that's debatable) a hole would be a non physical thing as there's really nowt there. But I can imagine how holes seem to travel through solids, a bit like a wave in water where the water doesn't move much but the energy can travel for miles.. Quote Link to post Share on other sites
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