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Homework Help: Electrical circuit?

  1. Feb 5, 2017 #1
    The student engineer of a campus radio station wishes to verify the effectiveness of the lightning rod on the antenna mast shown in the figure. The unknown resistance Rx is between points C and E. Point E is a true ground but is inaccessible for direct measurement since this stratum is several meters below the Earth's surface. Two identical rods are driven into the ground at A and B, introducing an unknown resistance Ry.
    The procedure is as follows. Measure resistance R1 between points A and B, then connect A and B with a heavy conducting wire and measure resistance R2 between points A and C. Derive an equation for Rx in terms of the observable resistances, R1 and R2. A satisfactory ground resistance would be Rx < 2.00Ω. In our case, measurements give R1 = 21.4 Ω and R2 = 10.67 Ω. What is the value of the unknown resistance Rx?

    This is my electric circuit so far but i am getting wrong answer ? I must be doing something wrong. Please help
    Here the picture of the my attempt;
    A C B
    | | |
    Ry Rx Ry
    | | |

    This my circuit for the first part of the question and then R1 = Ry/2 ---2 [the resistance between A and B].
    then ;
    the second circuit diagram :
    A C B
    | | |
    Ry Ry Rx
    | | |

    The difference is now Ry and Ry are connected in parallel.
    calculation ;
    So resistance R2 between A and C is R2= (Ry/2) +Rx ---1

    from ---1 and ----2 :
    Rx = R2 - Ry/4
    Last edited by a moderator: Feb 5, 2017
  2. jcsd
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