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Thread: Examples of Ohm's Law in Everyday Life - and the question of resistance

  1. #1 Examples of Ohm's Law in Everyday Life - and the question of resistance 
    ...matter and pixie dust wegs's Avatar
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    Posted this on the ''other'' site, thought I'd also share it here. It's cool to see science at work in everyday appliances and utilities.

    So, I looked up the meaning of resistance in this case, and it's a measure of the opposition to current flow in an electrical circuit. Why is opposition (resistance) necessary in a circuit?

    https://studiousguy.com/examples-of-...everyday-life/


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    Bullshit Intolerant PhDemon's Avatar
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    "Necessary" is the wrong word, it's just there as a property of the material the current is passing through... It's a bit like friction in mechanical systems... Ohm's Law and related equations just define it and quantify it.


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    ...matter and pixie dust wegs's Avatar
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    Ahh, that makes sense! Okay, thanks. Friction is a much better word, but resistance is the word used in the formula.

    How would you know that the flow within a circuit has resistance? Like from an observation to be able to quantify it?
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    Bullshit Intolerant PhDemon's Avatar
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    Careful! I used friction as an analogy, friction and resistance aren't the same thing...

    Resistance is a measured thing, you apply a known voltage across the material and measure the current passing through it. The resistance is the ratio of voltage to current (this is what Ohm's law says mathematically).

    How resistance arises is quite interesting, if we consider a metal, for example, the bonding is positive metal ions surrounded by delocalized electrons, when a voltage is applied these electrons move through the material as a current. They are not perfectly free to move though, the positive metal ions are like an obstacle course and collisions between electrons and ions restrict the flow... (Incidentally this causes the metal to heat up, this is how old style light bulbs work).

    In insulators where there are no free electrons it is like an obstacle course filled with concrete (another analogy!) and the current flow is tiny leading to a very high resistance.
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  6. #5  
    ...matter and pixie dust wegs's Avatar
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    Quote Originally Posted by PhDemon View Post
    Careful! I used friction as an analogy, friction and resistance aren't the same thing...

    Resistance is a measured thing, you apply a known voltage across the material and measure the current passing through it. The resistance is the ratio of voltage to current (this is what Ohm's law says mathematically).
    Okay. So, outcome for lack of a better word, would have been impacted by resistance, and that needs to be measured.

    How resistance arises is quite interesting, if we consider a metal, for example, the bonding is positive metal ions surrounded by delocalized electrons, when a voltage is applied these electrons move through the material as a current. They are not perfectly free to move though, the positive metal ions are like an obstacle course and collisions between electrons and ions restrict the flow... (Incidentally this causes the metal to heat up, this is how old style light bulbs work).

    In insulators where there are no free electrons it is like an obstacle course filled with concrete (another analogy!) and the current flow is tiny leading to a very high resistance.
    I see, but let me clarify...so the ''obstacle course'' of sorts, is known as resistance?

    That is pretty cool, your explanation. All this is going on when I turn on my ceiling fan? lol
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    Bullshit Intolerant PhDemon's Avatar
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    If there was no "obstacle course" there would be no resistance, resistance is a measure of how "difficult" the "obstacle course" is. Easy to pass "obstacles" = low resistance.
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    ...matter and pixie dust wegs's Avatar
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    Quote Originally Posted by PhDemon View Post
    If there was no "obstacle course" there would be no resistance, resistance is a measure of how "difficult" the "obstacle course" is. Easy to pass "obstacles" = low resistance.
    Perfect, I get it, now.

    Look at this link: https://www.allaboutcircuits.com/tex...-1/resistance/

    There would be more resistance in a lamp circuit than in a thick piece of wire.

    From the link - This resistance serves to limit the amount of current through the circuit with a given amount of voltage supplied by the battery...

    So if resistance didn't exist, would there be an explosion?
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    Moderator Moderator Janus's Avatar
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    I'm going to have to take exception with something stated in that article. It said that controlling the speed of a ceiling fan is done by increasing the "resistance" of the regulator. That actually is a really bad way to do this and can actually damage the fan motor. Ceiling fans will use either capacitors or solid state "duty cycle controllers" not variable resistors. Both of these methods rely on the fact that the fans are supplied by AC and not DC current.
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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  11. #10  
    ...matter and pixie dust wegs's Avatar
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    Quote Originally Posted by Janus View Post
    I'm going to have to take exception with something stated in that article. It said that controlling the speed of a ceiling fan is done by increasing the "resistance" of the regulator. That actually is a really bad way to do this and can actually damage the fan motor. Ceiling fans will use either capacitors or solid state "duty cycle controllers" not variable resistors. Both of these methods rely on the fact that the fans are supplied by AC and not DC current.
    i read an article that in India, most everyone has ceiling fans in every room, as opposed to AC. The article stressed the importance of buying the ''right'' regulator, as this will save energy. Apparently, the regulator controls the voltage.
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