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Voltage, Current

  1. Nov 15, 2006 #1

    Air

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    Can I have some information about these topics?

    • Voltage
    • Current
    • Resistance
    • Internal Resistance

    Thank You in Advance. o:)
     
  2. jcsd
  3. Nov 15, 2006 #2
    You need to be a little more specific.
     
  4. Nov 15, 2006 #3
    Last edited by a moderator: Apr 22, 2017
  5. Nov 15, 2006 #4

    russ_watters

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    Staff: Mentor

    Questions that general/vague will at best get you a reference to google or a wik link. You'll need to be more specific if you want some actual answers.
     
  6. Nov 15, 2006 #5
    Voltage = potential difference between two points
    Current = rate of change of charge with time
    Resistance = proportional to the voltage and inversely proportional to current
    Internal Resistance = Thevenin resistance seen by outside source
     
  7. Nov 16, 2006 #6

    Air

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    Thank You. I needed information like this. :smile:
     
  8. Nov 16, 2006 #7

    Air

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    What is Internal Resistance in relation to EMF?
     
  9. Nov 16, 2006 #8
    Think of it analogous to water flowing from an elevated tank through a small hose.

    Voltage is the pressure behind the water which corresponds to amount of water in the tank pushing down.

    Current is the speed of the water.

    Resistance is something in the hose obstructing the path of water flow.

    Internal resistance is the resistance of the water having friction with pipe walls.
     
  10. Nov 19, 2006 #9

    Air

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    Thats a very good analogy. Thanks. :smile:

    ______________________________________________________

    Can someone answer this question:

    What is Internal Resistance in relation to EMF?
     
  11. Nov 19, 2006 #10

    NoTime

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    What do you mean by internal resistance?
    Do you disagree with Mindscrape's definition?

    E=IR
     
  12. Nov 19, 2006 #11

    Gza

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    Well, if you have a given EMF, generated by a magnetic field changing in time, and are near some circuit or wire, you can just use good ol' ohms law to find the resistance:

    V=IR, or using different notation for your EMF, EMF=IR, or R=EMF/I, so the reistance in the circuit is proportional to the strength of the EMF, and inversely proportional to current.
     
  13. Nov 22, 2006 #12

    Air

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    The Voltage that is lost in the Power supply.
     
  14. Nov 22, 2006 #13

    NoTime

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    Usually, for most things, it's negligable.
    For actively regulated power supplys it can be 0 or even negative.

    If it is a factor, then the power supply resistance gets added to the rest of the resistance in the circuit.
     
  15. Nov 23, 2006 #14

    Air

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    Does this affect the circuit in any way?
     
  16. Nov 23, 2006 #15

    Hootenanny

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    Yes, in exactly the same way a normal resistor would. Suppose you have a cell with a 12V emf and 1[itex]\Omega[/itex] internal resistance. This would be equivalent to a circuit containing a 12V cell with no internal resistance, in series with a 1[itex]\Omega[/itex] resistor.
     
  17. Nov 23, 2006 #16

    Air

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    I see.

    Is it dangerous if the resistance gets high? If so why and what happens?
     
  18. Nov 23, 2006 #17

    Hootenanny

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    Resistors dissipate energy, how do you suggest they do this?
     
  19. Nov 23, 2006 #18

    Air

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    Resistance serves to limit the amount of Current through the circuit with a given amount of Voltage supplied by the battery.
     
  20. Nov 23, 2006 #19

    Hootenanny

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    Yes, it does this by dissipating (removing) energy (from the circuit). This energy is dissipated as heat. Therefore, if you have a high resistance together with a high current flow, then large amounts of heat will be dissipated.
     
  21. Nov 26, 2006 #20

    Air

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    After lots of heat is dissipated, does the Resistance, Voltage or Current change (i.e go lower or higher)?

    I thank all the people who have helped me so far. You have increased my knowledge. :smile:
     
  22. Nov 26, 2006 #21

    Hootenanny

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    As the temperature of a conductor increases, the resistance of that conductor also increases (note that a resistor is a conductor). Therefore, we have an example of positive feedback in a resistor; the resistance causes an increase in temperature of the resistor. This in turn increases the resistance of the resistor, thus further increasing the resistance. Therefore, the resistance of the resistor will increase.
     
  23. Dec 1, 2006 #22

    Air

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    Is it possible to have an electrical product that has Zero Internal Resistance?
     
  24. Dec 1, 2006 #23

    Hootenanny

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    Some materials are superconductors, i.e. at low temperature have a zero resistance, if that is what you mean.
     
  25. Dec 1, 2006 #24

    Air

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    No I mean the Internal Resistance which is The Resistance within a voltage source, such as an Electric Cell or Generator.

    So...Can a Electric Cell be made so that it has no Internal Resistance or is it impossible?

    (If you do not understand my question then please ignore it. :smile:)
     
  26. Dec 1, 2006 #25

    Hootenanny

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    No, it is not possible to create any electrical device (cell, battery, generator) with a zero internal resistance. However, in some cases where the load resistance is large compared to the internal resistance, it is possible to ignore the internal resistance.
     
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