# Homework Help: Electrical circuit?

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1. Feb 5, 2017

### ujjwal3067

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?

thanks:
Here the picture of the my attempt;
A C B
| | |
Ry Rx Ry
| | |
-------------------
E

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
| | |
---------------
E

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