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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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The insulation resistance of a cable length 10 km is 1 MΩ. For a length of 100 km of the same cable, the insulation resistance will be
1 MΩ
10 MΩ
0.1 MΩ
0.01 MΩ
0.1 MΩ
C is correct because the insulation resistance is inversely proportional to the cable length, so increasing the length by a factor of 10 decreases the resistance by a factor of 10.
Initial length L1 = 10 km, Initial resistance R1 = 1 MΩ, Final length L2 = 100 km.
R∝L1
Understanding the Relationship
The insulation resistance of a cable is inversely proportional to its length. This is because a longer cable offers more paths for leakage current through the insulation.
R×L=constant
Set up the Equation
Since R1L1=R2L2, we can solve for R2 given the known values.
R2=R1×L2L1
Calculate the Result
Substitute the values R1=1 MΩ, L1=10 km, and L2=100 km into the formula.
R2=1×10010=0.1 MΩ
C is correct because the insulation resistance is inversely proportional to the cable length, so increasing the length by a factor of 10 decreases the resistance by a factor of 10.
This concept is similar to how the leakage resistance of a capacitor dielectric changes with surface area, which is a fundamental principle in electrostatic shielding and cable design.