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Difference between voltage and voltage drop?

  1. Nov 29, 2010 #1

    what is the difference between voltage and voltage drop?
    in text i read as follows and i could not get

    When the voltage on the base is very close to 0.6v, the transistor is just at the point where it is turned ON and the voltage on the collector will be say 8v for a 9v supply.
    If the voltage on the base rises by 50mV, the transistor will turn ON more and the voltage on the collector will drop to say 3v.
  2. jcsd
  3. Nov 29, 2010 #2
    Re: voltage

    There is no difference except a little bit of connotation perhaps. The voltage between two points in a circuit is the same as the voltage drop between those points. To me, the latter expression has a verbal hint that the difference in voltage is driving a current (say, through a resistive element) and we lose some of the potential in doing so.

    In your example "drop (to)" simply means that the voltage is decreased to 3 V. A "voltage drop" is usually a relative measure of how much potential is lost across a part of the circuit.
  4. Dec 4, 2010 #3
    Re: voltage

    i'm so sorry sir SEngstrom.i can't understand.if don't mind can you explain it more,the difference between voltage drop and simply voltage?
    up to my concepts there is no difference,the voltage between two points is same if there is no any passive element is installed between these two points if there is no any passive element,voltage remain same but it is only in ideal case.wires also have its own resistance some voltage drops must happens.
    is voltage and potential difference resembles with each other i mean what is the relation between voltage and potential difference?
  5. Dec 4, 2010 #4
    Re: voltage


    There is no physical definition of the voltage at a single point. All voltages are differences in electric potential from one place to another.

    If one were to read that the "voltage of the base is 0.6V, then it is implies that the voltage of the base is 0.6 volts above the voltage of the emitter.

    Usually in a circuit, there is a designated ground. In this case voltage at points in the circuit refer to what you get if you attach your DVM negative probe to ground.
  6. Dec 4, 2010 #5
    Re: voltage

    A drop.
  7. Dec 4, 2010 #6


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    Re: voltage

    We can take a 12 volt battery with nothing connected to it except a voltmeter and measure 12 volts. We usually don't consider this voltage drop. If we connect two light bulbs of the same wattage in series to this battery each bulb will have 6 volts across it. This is a case when we consider each bulb is dropping 6 volts. So usually we need a current through a device in a series circuit before we call the voltage measured across said device to be a voltage drop.
  8. Dec 4, 2010 #7


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    Re: voltage

    I've only heard of voltage drop as referring to passive, dissipative devices, eg. resistors or diodes. Even when a battery has a current, we don't refer to it's voltage as a voltage drop -- do we?
  9. Dec 5, 2010 #8


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    Re: voltage

    I was referring to the drop across each bulb.
  10. Dec 5, 2010 #9
    Re: voltage

    I dont think the example in post 1 has anything to do with the phrase "voltage drop".

    generally I think voltage drop refers to the potential across a (passive) component, while voltage refers to the potential wrt 0v.
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