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Why wouldn't the bulb light up in this circuit diagram?

  1. Oct 19, 2016 #1
    • Member advised to use the homework template for posts in the homework sections of PF.

    Why is this wrong? Does the (v) need to be on the right side?

    Is this right?

    Voltage symbol V is measured in |_____ joules (J)| <--
    Voltage is a measure of the amount ______<--- volts| done on a unit _____<---?
  2. jcsd
  3. Oct 19, 2016 #2


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    What do you use a voltmeter for? What do you use an ammeter for?
  4. Oct 19, 2016 #3
    Voltmeter to measure voltage between two points.
    Ammter to measure current in a circuit
  5. Oct 19, 2016 #4


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    Staff: Mentor

    Correct. And one of them looks like a short circuit and the other like an open circuit. Which is which? :smile:
  6. Oct 20, 2016 #5


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    Electric charge circulates very much like water through a circuit.
    The electric charge does work as it flows through the circuit and loses electric potential energy in the process.
    Positive charge starts at the positive terminal of the battery, the long thin line, with a high electric potential or voltage and flows towards the negative terminal, the short fat line, and does work in the various components that it flows through, thereby losing electric potential energy in the process.
    The voltmeter measures the electric potential difference between its terminal and thus tells us how much work the charge did between the two connecting points where the voltmeter is connected.
    On the other hand an ammeter tells us how much electric charge is flowing through it per second.
    This circuit is all about the lightbulb, the X inside of the cirle component.
    We are especially interested in the current through the lightbulb and the potential difference caused by the lightbulb in this circcuit, or how by how much the potential has dropped as the charge flows through it.
  7. Oct 20, 2016 #6
    Is it because as current goes to the voltmeter and ammeter it loses "energy" meaning the bulb wont light up?
  8. Oct 20, 2016 #7


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    In the diagram the ammeter measures the current through itself, not through the lightbulb, also the voltmeter is measuring the potential difference between one side of the light bulb and the + of the battery and not the potential difference of the lightbulb itself, from that viewpoint the meters are not applied or wired correctly.
  9. Oct 20, 2016 #8


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    Which meter will be almost an open circuit and which one will be almost a short circuit?
  10. Oct 20, 2016 #9


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    Have a think about what makes an ideal voltmeter and an ideal ammeter. For example you wouldn't want a voltmeter or Ammeter to effect the way a circuit works when you connect it. This means volt meters and Ammeters are different (see post 8). If they are connected in the wrong place (eg an ammeter where the volt meter should be) then it WILL effect the circuit (and may even be damaged).
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