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Resistence help

  1. Oct 2, 2008 #1
    A 10 ohm resistor in a series with a bulb and a 12v source.

    a) If the 8.0V is across the bulb, what is the voltage across the resistor?
    I wrote 4v, is this correct?

    b) What is the current in the circuit? I wrote 1.5A, is this correct?

    c) What is the resistence of the bulb? Could someone please tell me the formula I would need to know to complete this question?
     
  2. jcsd
  3. Oct 2, 2008 #2

    Redbelly98

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    a) correct
    b) no. how did you get 1.5A?
    c) what formula do you know of that deals with voltage, current, and resistance?

    p.s. welcome to PF.
     
  4. Oct 2, 2008 #3
    for question " b) " i got "I = V/R" from Ohm's Law. I realize I mistakenly wrote 1.5A, I meant 1.2A, is that incorrect still?

    for question "c)" I dont see anything that pertains to it other than Ohm's law, " R = V/I " but I dont have the current, so i do not understand how to solve it.

    Would the correct way to do it be " R = 4/1.2 " ??
     
    Last edited: Oct 2, 2008
  5. Oct 2, 2008 #4

    Redbelly98

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    b) Okay, correct formula. What are you using for V and R that gives you 1.5A?

    c)
    See part (b)
     
  6. Oct 2, 2008 #5
    you said part b) was wrong though.. or did you not read it after I re-edited it?
     
  7. Oct 2, 2008 #6

    Redbelly98

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    b)
    Umm, 1.2A is also not right. (I did miss your edit.) Apparently you are saying
    12 V / 10 Ω = 1.2 A
    But it is wrong (for this circuit) to use 12V and 10Ω together like that.

    What do you know about the current through each component, given that they are in series?

    c)
    Once you have gotten a correct answer for (b), you can use that information.
     
  8. Oct 2, 2008 #7
     
  9. Oct 2, 2008 #8
    You have voltage and resistance of the resistor, so you can get the current through it.
     
  10. Oct 2, 2008 #9
    oh so it would be I = 4/10 which is .4?
     
  11. Oct 2, 2008 #10

    Redbelly98

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    Yes.

    Take a look at what your textbook says about circuit components that are in series, and the current through them.
     
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