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Resistor value

Discussion in 'General Electronics Discussion' started by Chassis, Jun 4, 2015.

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  1. Chassis

    Chassis

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    Apr 21, 2015
    Good day.I have a question,I'm sorry if it may sound stupid. To what does it refer if you get a question as "Determine the value of R3" if R3 is 120Ohms.does it refer to the color code? Brown,Red,Brown? The question doesn't say anything about color codes.
     
  2. Y2KEDDIE

    Y2KEDDIE

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    Sep 23, 2012
    Possibly it's wattage rating.
     
  3. ramussons

    ramussons

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    Jun 10, 2014
    How did this value of 120 Ohms come from? Was there a calculation?
    Can you ask the question in a different style?

    "value of R3" can only be "Ohms",
     
    davenn likes this.
  4. davenn

    davenn Moderator

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    Sep 5, 2009
    show us the full question and any circuit pic associated with it

    the Q is obviously referring to a circuit that you haven't told us about
     
  5. Chassis

    Chassis

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    Apr 21, 2015
    Sorry for the bad quality.all the questions for the circuit is below.I understand everything except the one above.

    For the given circuit we have the following:
    R1 = 200 ohm, R2 = 50 ohm and R3 = 120 ohm
    The volts drop V3 across R3 is measured as 160V
    Calculate the following:

    (a) The value of the current flow through R1, if It = 4 A.
    (b) The total overall resistance of R1 and R2 in parallel
    (c) Determine the value of R3
    (d) The total resistance of the circuit
     

    Attached Files:

  6. davenn

    davenn Moderator

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    Sep 5, 2009



    do you know how to work out parallel resistors ?

    you are already told it is 120 Ohms


    work out the parallel value and add it to the 120 Ohms


    Dave
     
    Last edited: Jun 5, 2015
  7. Chassis

    Chassis

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    Apr 21, 2015
    The question they are asking sounds very senseless if they already giving it to me (120 Ohm) I am sorry I waisted your time. So the resistor value always refers to the resistor Unit?
     
  8. Kiwi

    Kiwi

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    Jan 28, 2013
    I am a little confused.

    They give R3 value as 120Ω and voltage drop as 160V.
    Using Ohms Law: I = V/R = 160/120 = 1.333Amps.
    In (a) they give It as 4A, so V = I x R = 4 x 120 = 480V
    What happened to the given voltage of 160V???

    (b) Parallel resistance of R1 and R2 network is easy enough to calculate using 1/Rp = 1/R1 + 1/R2

    (c) They have already given you resistance of R3 as 120Ω. Maybe they want wattage of R3 using P = V x I. What voltage do you use?

    (d) Total resistance = Rp + R3

    What am I missing, or is the question all messed up?
     
  9. Chassis

    Chassis

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    Apr 21, 2015
    Refers to the resistor Ohms?
     
  10. davenn

    davenn Moderator

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    Sep 5, 2009

    yes I saw that too ... it just doesn't make sense ... there seems to be too many errors in this question
     
  11. Chassis

    Chassis

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    Apr 21, 2015
    This question was asked in last years exam papers. can someone work this out or draw a circuit with more or less the same questions and answers in order for me to apprehend it.
     
  12. Chassis

    Chassis

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    Apr 21, 2015
    Or can someone please send me a link of series-parallel resistor circuit samples including questions and answers.thanks in advance guys.
     
  13. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Do you have a copy of the exam paper with that question?
    Adam
     
  14. Chassis

    Chassis

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    Apr 21, 2015
    I hope the attach will open,its pdf format.check out page 5.
     

    Attached Files:

  15. BobK

    BobK

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    Jan 5, 2010
    Yes, the question is self contradictory. If It is 4A, and V is 160, then R3 has to be 40Ω.

    Bob
     
  16. Chassis

    Chassis

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    Apr 21, 2015
    Got you there Bob! So the reason why they have mentioned R3 as 120ohm refers only to question (d) ? that's if you managed to open my attachment.
     
  17. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    I think they want you to show the workings of how you would determine the value of the resistor including the other two. You would also have to indicate the supply voltage also.
    Adam
     
  18. davenn

    davenn Moderator

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    Sep 5, 2009
    that's pointless, as said earlier, the value is given, there isn't anything to calculate

    Q parts a, b and d are valid.
    c doesn't make sense when it's already given and as again already been stated earlier
    I total cannot be 4A if the V drop across 120 Ohms is 160V

    the whole Q has a lot of problems
     
  19. Chassis

    Chassis

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    Apr 21, 2015
    Anyone have links with series-parallel Resistor circuit Exercises?
     
  20. davenn

    davenn Moderator

    13,381
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    Sep 5, 2009
    please show a little effort ....
    Im sure you are capable of typing that into google ;)

    Dave
     
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