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Conductors and Insulators
11 questions By Tony R. Kuphaldt
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Question 1 of 11
Given two lengths of metal wire, which one will have the least electrical resistance: one that is short, or one that is long? Assume all other factors are equal (same metal type, same wire diameter, etc.).
Reveal answerThe short wire will have less electrical resistance than the long wire.
Notes:Many analogies exist to express this concept: water through a pipe, compressed air through a hose, etc. Which pipe or hose is less restrictive: the short one or the long one?
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Question 2 of 11
Given two lengths of solid metal wire with round cross-sections, which one will have the least electrical resistance: one that is small-diameter, or one that is large-diameter? Assume all other factors are equal (same metal type, same wire length, etc.).
Reveal answerThe large-diameter wire will have less electrical resistance than the small-diameter wire.
Notes:Many analogies exist to express this concept: water through a pipe, compressed air through a hose, etc. Which pipe or hose is less restrictive: the skinny one or the fat one?
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Question 3 of 11
What is the difference between materials classified as conductors versus those classified as insulators, in the electrical sense of these words?
Reveal answerElectrical “conductors” offer easy passage of electric current through them, while electrical ïnsulators” do not. The fundamental difference between an electrical “conductor” and an electrical ïnsulator” is how readily electrons may drift away from their respective atoms.
For an illustration of electron mobility within a metallic substance, research the terms electron gas and sea of electrons” in a chemistry reference book.
Notes:It is important to realize that electrical “conductors” and “insulators” are not the same as thermal “conductors” and “insulators.” Materials that are insulators in the electrical sense may be fair conductors of heat (certain silicone gels used as heat-transfer fluids for heat sinks, for instance). Materials that are conductors in the electrical sense may be fair insulators in the thermal sense (conductive plastics, for example).
For 10.
I used the second entry for Mica, phlogopite, at https://www.engineeringtoolbox.com/dielectric-strength-electrical-insulator-d_2185.html
with a dielectric strength of 31.5 E6 V/m.
My calculation using dimensional analysis: 50 mm x (10 E-3 m/1 mm) x (31.5 MV/m) = 1.58 MV
This is way off from 1 kV - what went wrong?
For 11.
Could you just take a battery, two wires, a small and measured piece of the insulator, and connect one of the wires to one end of the material and then the other wire to the other end, and bracket the voltage from ammeter readings until a small enough range is found for the voltage at which the insulator becomes a conductor? Taking account of the size of the material, of course.
As for the measurement of V/m - is the measured distance for m from one end of the circuit to the other, rather than any particular length of the piece of material?