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Homework Help: Calculate the equivalent resistance of the circuit

  1. Apr 5, 2010 #1
    1. The problem statement, all variables and given/known data

    a 50 ohm resistor, an unknown resistor R, a 120 volt source and an ammeter are connected in a compelete circuit. the ammeter reads 0.50 ampere

    1)calculate the equivalent resistance of the circuit

    2)determine the resistance of resistor r

    2. Relevant equations

    a = 0.50 A
    v = 120
    r1 = 50 ohm
    r2 = ?

    R = R1 + R2 + R3 + ...

    3. The attempt at a solution

    the problem is a series circuit so how do i know the other resistance if i know the first one?
  2. jcsd
  3. Apr 5, 2010 #2
    I`ll try to give you few hints..

    for part(1) : it is asking for the equivalent resistance .. you are give the equivalent (total) voltage which is the source voltage(120v), and the total current which is simply the reading of the ammeter (0.5 ampere) .. so can you determine now the equivalent resistance? ..

    for part(2) : after getting the equivalent resistance .. you can find the resistance for r noting that you are dealing with a situation where the two resistors are in series (Req = R1 +R2 ) ..

    is it clear enough (>> well, I guess so ) .. :)
  4. Apr 5, 2010 #3
    so for equivalent resistance i should do v/a to get r?
    i did 120v/0.50a and got 240 r so that is the equivalent resistance
    and for the resistance of r i do 240r + 50r and get 290 r is this correct?
  5. Apr 5, 2010 #4
    Think it through;

    The equivalent resistance is the total resistance of all the circuits components. You have the right method of finding total resistance in using [tex]R_{T}=R_{1}+R_{2}+...+R_{n}[/tex] so your [tex]R_{T}[/tex] value is 240 Ohm's, so what is [tex]R_{2}[/tex]?
  6. Apr 5, 2010 #5
    oh r2 should be 190 since they need to add up to 240
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