The student engineer of a campus radio station wishes to verify the effectiveness of the lightning rod on the antenna mast (Fig. P18.55). The unknown resistance Rx is between points C and E. Point E is a ?true ground,? but is inaccessible for direct measurement, since the stratum in which it is located 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 for finding the unknown resistance Rx 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.

(a) Derive a formula for Rx in terms of the observable resistances R₁ and R₂.

(b) A satisfactory ground resistance would be Rx 1 = 13 ? and R₂ = 6.0 ??

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