Two conductors are made of the same material and have the same length. Conductor A is a solid wire of diameter 1.0 mm. Conductor B is a hollow tube of outside diameter 2.7 mm and inside diameter 2.0 mm. What is the resistance ratio RA/RB, measured between their ends?

The resistance ratio is 3.23

Explanation:

Since the conductors are made of the same material and length the product of the resistivity and length of the conductor are the same for both conductors and is constant.

R = ρL/A = constant / A

So RA = constant

And RaAa = RbAb

Ra/Rb= Ab/Aa

D = 1mm = 1×10‐³m

Aa = πD²/4 = π(1×10-³)²/4 = 7.85×10-⁷ m²

D1 = inner diameter of conductor B = 2.0mm = 2×10-³m

D2 = outer diameter of conductor B = 2.7mm = 2.7×10-³m

Ab = π(D2²-D1²)/4 = π((2.7×10-³)²-(2.0×10-³)²)/4 = 2.58×10-⁶m²

So,

Ra/Rb= Ab/Aa = 2.58×10-⁶/7.85×10-⁷ = 3.23

The resistance ratio is 3.23. This makes sense because a larger cross sectional area means more electrons can flow through the conductor per time and so lesser resistance. Conductor B has a larger cross sectional area and so lesser resistance when compared to conductor A.

nec chapter 5 contains

c. information on special occupancy areas

nec chapter 6 covers

a. special equipment

which of the following rules contain the words shall or shall not and must be adhered to?

b. mandatory rules

which of the following rules identify actions that are allowed but not required and typically cover options or alternative methods?

c. optional rules

which of the following serves as the introduction to the nec and provides an overview of the book?

a. nec article 90

organizations that test products for safety are

c. nrtls

the nec is published by the

a national fire protection association

the nec is divided into

b. 9 chapters

the nec provides informative annexes for

c. informational materials and examples

two terms from nec article 100 that trainees should become familiar with are

b. labeled and listed

explanation: