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Thread: How is that every device in house gets the right amount of energy

  1. #1 How is that every device in house gets the right amount of energy 
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    It is probably a trivial question but from my understanding when I have simple circuit with 3 light bulbs one after another at the wire the second bulb will get decreased voltage compared to the first(so it will give less light than first), the third bulb will get decreased voltage compared to the second (so it will give less light than second) - so how is that in the house every bulb(and actually every electronic device) gets the right amount of energy,voltage no matter how many devices u connect to your house circuit


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    Genius Duck Moderator Dywyddyr's Avatar
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    Mainly because the items in a house aren't wired up "one after another".
    Series and parallel circuits - Wikipedia, the free encyclopedia
    Ring circuit - Wikipedia, the free encyclopedia


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    In addition, your understanding of what happens if you string three lights together is incorrect. Assuming the lights are identical, then they will divide the source voltage equally among themselves. (if the source is 120v, each light will see 40v.)
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    Cooking Something Good MacGyver1968's Avatar
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    All devices in your house are connected in parallel. In a parallel circuit, everything gets the same voltage...the current (amps) add up. That's why your breaker box is rated in amps.
    Fixin' shit that ain't broke.
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    Quote Originally Posted by fghf76 View Post
    It is probably a trivial question but from my understanding when I have simple circuit with 3 light bulbs one after another at the wire the second bulb will get decreased voltage compared to the first(so it will give less light than first), the third bulb will get decreased voltage compared to the second (so it will give less light than second) - so how is that in the house every bulb(and actually every electronic device) gets the right amount of energy,voltage no matter how many devices u connect to your house circuit

    Your first statement is nearly correct, but your second is based on an incorrect assumption.

    The first situation is called wired in series. The circuit is constructed by wiring from the voltage source through each element of the circuit in turn then back to the voltage source. In such a series circuit, the current flowing through each element is the same, and the resistance of each element will determine how much voltage is dropped across it. So in your three identical bulb example, the voltage will drop as you describe. But of course if the source voltage is 120 Volts and each bulb is designed for 40 Volts, then they will all shine equally brightly and correctly. If each bulb is 120 Volts rated, they will all shine equally dimly.

    House wiring is connected in parallel, which is different. Imagine two parallel wires. One is connected to the positive terminal of the voltage source, the other to the negative terminal. You can connect any number of individual items between the parallel wires - each one connected between the positive wire and the negative wire. Now each item will receive the same voltage, but take a different amount of current according to its needs. The total current flowing in the parallel wires is the sum of the current taken by each item, so there is a practical limit to how many items can be fed from a parallel circuit, according to how much total current the parallel wires can handle.

    Think of the wires as water pipes. The voltage is like the water pressure inside the pipes. The current is like the amount of water actually flowing through the pipes.

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    Short answer - Ohm's Law.
    It is probably a trivial question but from my understanding when I have simple circuit with 3 light bulbs one after another at the wire the second bulb will get decreased voltage compared to the first
    If they are in series - yes. However household devices are generally wired in parallel, not series. In that case each bulb gets the same voltage.
    so how is that in the house every bulb(and actually every electronic device) gets the right amount of energy,voltage no matter how many devices u connect to your house circuit
    Every device sees the same voltage. Every device has a specific impedance (resistance) while it is operating. The device's impedance controls how much power (not energy) it gets. Thus a 100 watt light bulb presents a lower impedance, draws more current, and uses more power than a 40 watt light bulb.
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    Household devices are setup so that they only draw the power they use, that's why you have adapters and ballasts and such. Otherwise everything would just short circuit
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    Quote Originally Posted by ScienceNoob View Post
    Household devices are setup so that they only draw the power they use, that's why you have adapters and ballasts and such. Otherwise everything would just short circuit
    Not so much 'set up', but every electrical device has a property called impedance. This is a type of resistance - but too complex to worry about for the purposes of this discussion - and means that each device only draws the current it needs.

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    Quote Originally Posted by ScienceNoob View Post
    Household devices are setup so that they only draw the power they use, that's why you have adapters and ballasts and such.
    Well, those adapters are generally to step down voltage and/or regulate current.
    Otherwise everything would just short circuit
    ?? That's generally not what short circuit means. You can damage something by feeding it with the wrong voltage, but it's not a short circuit, it's just the wrong voltage. Note that in the US, the overwhelming reason that external AC/DC adapters are used is safety, and second is cost. It's trivial to design any product to work with 120 VAC but safety certifications take a lot longer, and in general it's more expensive.
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