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Homework Help: Need help!

  1. May 12, 2010 #1
    Need urgent help!

    14e28ih.jpg
    Determine the total resistance between A and B.

    How much will I1 be if Vab is 10 volts.

    ... The resistors are in parallel. Resistors are ohms.
     
  2. jcsd
  3. May 12, 2010 #2
    Re: Need urgent help!

    If you show what you have tried already there are people here who may help.Is there a gap at R5?
     
  4. May 12, 2010 #3
    Re: Need urgent help!

    Thats the thing, I am completely unaware of what I need to be doing. There is no gap at R5, it is also a 220 resistor placed there. I am just looking for some help on how to go about answering those questions. This is somewhat of a preview of what I will be taking in a next class, and I wanted to get some sort of understanding instead of going in completely blind.
     
  5. May 12, 2010 #4
    Re: Need urgent help!

    Start by looking at the three resistors R3,R4 and R5.These can be replaced by a single resistor.What is its value?
     
  6. May 12, 2010 #5
    Re: Need urgent help!

    620 ohms
     
  7. May 12, 2010 #6
    Re: Need urgent help!

    Do you mean 660 ohms?If so sketch your circuit with this resistor replacing R3,R4 and R5.You will see that you now have two resistors in parallel.What is the value of the single resistor that can replace these two?
     
  8. May 12, 2010 #7
    Re: Need urgent help!

    ops, yes i meant 660 ohms. the resistor that would replace the two in parallel would be 1480
     
  9. May 12, 2010 #8
    Re: Need urgent help!

    It is 660 ohms.For resistors in parallel you use the formula
    1/R=1/R1+1/R2 .The single resistor is much smaller than 1480
     
  10. May 12, 2010 #9
    Re: Need urgent help!

    i am not sure, this is all new, sorry!
     
  11. May 12, 2010 #10
    Re: Need urgent help!

    There is an equation you can use to work out the value of the single resistor that can replace the two resistors you have in parallel.I have given the equation above where R1 and R2 are the two resistors in parallel and R is the value of the single resistor that can replace them.Plug in the numbers for R1 and R2 and calculate R.
     
  12. May 12, 2010 #11
    Re: Need urgent help!

    um so that will be
    Rt= r1/r2= r1r2/ r1+r2
    which will equal around 365.7 ohms ?
     
  13. May 12, 2010 #12
    Re: Need urgent help!

    I get the same answer.Finally you have three resistors in series 365.7 ohms,100 ohms and 100 ohms.To work out the equivelent resistor for series arrangements you just add them as you did in post 5.
     
  14. May 12, 2010 #13
    Re: Need urgent help!

    mhm so 565.7 ohms
     
  15. May 12, 2010 #14
    Re: Need urgent help!

    Yes.
     
  16. May 12, 2010 #15
    Re: Need urgent help!

    Thank you for the help!
     
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