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Can't understand. Plz help!

  1. Dec 17, 2005 #1
    Ciao all. I have kind of a basic question but i don't really understand how it works. I don't know how it's named in english, but maybe "voltage controller". It's a screwdriver with a small light bulb that is used to see if there is voltage, on an outlet for example. You plug it into the "phase"(hot) wire hole and press your thumb against a metalic end at the end of the handle and if there is voltage the bulb lights up. So here's the question, how does it work? how do you complete the circuit. Maybe a small schematic plz. I know it may be a simple question so plzz enlighten me! 10x
  2. jcsd
  3. Dec 17, 2005 #2


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    Welcome, Omul_b.
    We just call those circuit testers. I've worked only with DC ones, and they have to be grounded. All that I can think of in the case that you're talking about is that it must be some sort of gas-discharge bulb that lights when it's in an EM field and modified by body capacitance. I really don't know, though.
  4. Dec 17, 2005 #3
    It is most likely a neon bulb inside the tester. Either the body capacitance or the actual path back through ground completes the circuit.
  5. Dec 17, 2005 #4
    I don't know about DC ones, but this one is not grounded, and it isn't a neon bulb (or i don't think so). It just looks like an ordinary light bulb. I still don't understand. Anyone ??
  6. Dec 17, 2005 #5
    I SERIOUSLY doubt it is a regular incandescent bulb.
  7. Dec 17, 2005 #6


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    Look at the glass bulb and see if there are two small, parallel electrodes inside. If so, it's a neon buld and works as Averagesupernova says where you body completes the path back to ground. The current through the circuit is very small but the potential difference across the two electrodes causes the neon to glow.

  8. Dec 17, 2005 #7
    I noticed that if i wear rubber boots on my feet the light is not that strong (BTW you were right, it's a neon bulb). And, for that matter, please tell me:
    1) i've heard a lot of stuff about the human body behaving like a "capacitor". How does this happen ? I mean if you connect a capacitor at one end of a circuit it wouldn't gather anything, would it? I mean there is no voltage across it. It's just like the birds standing on the electrical wire.
    2) If i were perfectly isolated from the ground, would it light up ?
    10x in advance and sorry about all the questions :)
  9. Dec 18, 2005 #8


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    Capacitors conduct current from A.C. sources. Your body is one side of the cap and the ground is the other.
  10. Dec 19, 2005 #9
    brief question in between~~

    How does a capacitor complete a series circuit?
    both sides of the capacitor is not connected... how does electrons flow? or does it even flow across the capacitor?

    if a battery positive terminal is connected to a resistor, then the resistor is connected to a capacitor, which is connected back to the negative terminal of the battery, would there be current through the resistor?

    sorry for the interruption~
  11. Dec 19, 2005 #10


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    You should start a new thread on this.

    In a resistor-capacitor charging circuit, capacitor voltage goes from nothing to full source voltage while current goes from maximum to zero, both variables changing most rapidly at first, approaching their final values slower and slower as time goes on. Current through the circuit is determined by the difference in voltage between the battery and the capacitor, divided by the resistance. As the capacitor voltage approaches the battery voltage, the current approaches zero. After a capacitor has fully charged (to the level of the volatge source), it acts as a open circuit (voltage drop with no current)
    Last edited: Dec 19, 2005
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