A+ Quiz with Pictures

Discussion in 'A+' started by UCHEEKYMONKEY, Nov 25, 2006.

  1. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    It isn't. But it is better than air!

    Harry.
     
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  2. Rafek

    Rafek Kilobyte Poster

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    13/20 :dry not that good really..

    I'd have to agree with Harry and others regarding the Silicone/mercury question, I too answered silicone as i can't believe mercury would have even been considered for such a product. *Waits for someone to correct me* :blink
     
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  3. HungryForHertz

    HungryForHertz Bit Poster

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    I could believe there was mercury in the thermal paste. I seem to remember hearing about it somewhere several years ago.
     
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  4. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    I think I'd like a reference for that....... :biggrin

    Harry.
     
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  5. fortch

    fortch Kilobyte Poster

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    I'm with Harry on the silicone thing -- although it doesn't remove heat, it just tranfers it, although not particularly well. Silicone is based on silicon atoms, and can be mixed with a multitude of elements to provide certain elemental properties. In most cases, it's electrical insulation and stability-under-heat that most applications are after.

    Thermal Conductivity of Elements

    As you can see, silicon is not bad, but not nearly as great as other elements (Copper and Silver). As far as Mercury, it *was* probably used extensively, but only as an amalgam -- that is, a kind of natural bonding agent with metals and alloys. It may not even be listed, particularly in thermal compounds, because of it's poor thermal conductivity. However, it's greatest asset is it's usability -- even in things like dental fillings :ohmy Besides, a thermal paste wouldn't be paste if it was made of pure silver -- which is a solid in it's natural state, and wouldn't deliver the seemless conduction that a stable thermal compound can provide. More to consider than just heat transfer, I'm afraid.

    As to the power supply issue, I think Bluerinse's description is outstanding -- with one clarification. A device being grounded needs to be proportionate to its size and power. For example, the reason the doorknob example sparks is because there is not enough surface area to dissipate the charge, and you become the path to ground. If that same doorknob were 10x it's size, there may not be a shock, because the potential gets drained away before it reaches a kinetic state. In the case of ESD, the difference of potentials requires the use of a groundstrap to remain at the same potential as the component being serviced. That said, it's obvious why you'd either wear a groundstrap, or develop the habit of keeping a hand on the chassis when performing work. All bets are off if you've built up a decent charge -- ESD can be thousands of volts, and even at low amperage, it can damage today's solid-state circuitry at the blink of an eye. The designed circuit is perfectly functional when the system is connected, and using the implied feed from the outlet. Things change rapidly when you introduce your own power supply to the equation, particularly when the chassis is insufficient to disperse the charge you've introduced.

    So, plugged in or not? I usually subscribe to conventional wisdom, but I have no issue with working on a PC, provided the supply is switched off in the back. ESD has a much greater path to ground through a dedicated direction, rather than the playground of the PC case. However... there seems to be evidence either way, particularly considering the ongoing debate of conventional vs electron theory, so I'll leave it at that :rolleyes: Regardless, if A+ says that way, then that way you shall go (if prepping for that exam)!
     
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  6. Bluerinse
    Honorary Member

    Bluerinse Exabyte Poster

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    Hmmm, I disagree with this.

    My understanding is that it is most likely *you* and not the door knob that is highly statically charged, your body has lost or gained some electrons, depending on what materials you have come into contact with (dragging shoes on nylon carpet, travelling in a car) and the amount of friction involved. This is known as the triboelectric effect The door handle will not be in the same charged state and when you touch it the spark (very high voltage but tiny current) is evidence that the two entities (you and the knob) are equalising their triboelectric state. You are in fact giving the door handle a jolt, as your charge is higher. Nothing to do with a path to ground! :biggrin
     
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  7. fortch

    fortch Kilobyte Poster

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    True... I just read my post, and that part even confuses me:oops: You are definitely building the charge, or gaining the requisite electrons (from, let's say, the carpet) and the doorknob is the recipient, being at a much different state. Since the flow of electrons *is* current flow, I often misuse the term 'path to ground' as the transfer of electrons in a circuit -- since that is what electricity desires. Why did I state I was the ground? Did the doorknob just rub itself across the carpet?

    Perhaps I was thinking of electrical noise in ground circuits, and their effect on commonly grounded adjacent circuits. Who knows? I do know that next time I'll pay more attention to what I type:biggrin
     
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  8. Bluerinse
    Honorary Member

    Bluerinse Exabyte Poster

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    Whatever you type fortch, it is always a pleasure to read.
     
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