# Conductors and Insulators

## Basic Electricity

• #### Question 1

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.).

• #### Question 2

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.).

• #### Question 3

What is the difference between materials classified as conductors versus those classified as insulators, in the electrical sense of these words?

• #### Question 4

Identify several substances that are good conductors of electricity, and several substances that are good insulators of electricity.

• #### Question 5

What naturally occurring substance is the best conductor of electricity?

• #### Question 6

Electrical wire is often rated according to its cross-sectional diameter by a gauge scale. Which is the larger-diameter wire size, 14 gauge or 8 gauge?

• #### Question 7

What disadvantages might there be to using undersized wire in an electrical power distribution system, where electricity is transmitted from generators (sources) to “loads” (devices requiring power) far away? What might happen if the wires we choose for this application were to have insufficient cross-sectional area?

• #### Question 8

What disadvantages might there be to using oversized wire in an electrical power distribution system, where electricity is transmitted from generators (sources) to “loads” (devices requiring power) far away? What might be bad about using wires with more than sufficient cross-sectional area for the purpose?

• #### Question 9

What does the breakdown voltage (also known as dielectric strength) rating for an electrically insulating substance mean?

• #### Question 10

How much voltage can a 50 μm thick piece of mica withstand before breaking down?

• #### Question 11

Design a circuit to test the breakdown voltage of a material. • deteriol January 01, 2022

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?

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• deteriol January 03, 2022
10 is my bad. micrometres, not millimetres.
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• D
dalewilson January 06, 2022
Actually, you were correct about the calculation error. The units were mistakenly listed as 50 mm, when they should have been 50 um as you suspected. We have corrected the mistake in the units and even provided some more clarity to the answer. Thanks for bringing this to our attention. Sorry, but I don't understand your question about measuring the current. The V/m value for breakdown voltage is for the thickness of the material. The rest of the circuit is not part of the length measurement.
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