# 12: Physics of Conductors and Insulators

• 12.1 Introduction to Conductance and Conductors
By now you should be well aware of the correlation between electrical conductivity and certain types of materials. Those materials allowing for easy passage of free electrons are called conductors, while those materials impeding the passage of free electrons are called insulators.
• 12.2: Conductor Size
It should be common-sense knowledge that liquids flow through large-diameter pipes easier than they do through small-diameter pipes (if you would like a practical illustration, try drinking a liquid through straws of different diameters). The same general principle holds for the flow of electrons through conductors: the broader the cross-sectional area (thickness) of the conductor, the more room for electrons to flow, and consequently, the easier it is for flow to occur (less resistance).
• 12.3: Conductor Ampacity
The smaller the wire, the greater the resistance for any given length, all other factors being equal. A wire with greater resistance will dissipate a greater amount of heat energy for any given amount of current, the power being equal to P=I2R. Dissipated power in a resistance manifests itself in the form of heat, and excessive heat can be damaging to a wire (not to mention objects near the wire!), especially considering the fact that most wires are insulated with a plastic or rubber coating, w
• 12.4: Fuses
Normally, the ampacity rating of a conductor is a circuit design limit never to be intentionally exceeded, but there is an application where ampacity exceedance is expected: in the case of fuses.
• 12.5: Specific Resistance
• 12.6: Temperature Coefficient of Resistance
You might have noticed on the table for specific resistances that all figures were specified at a temperature of 20o Celsius. If you suspected that this meant specific resistance of a material may change with temperature, you were right!
• 12.7: Superconductivity
Conductors lose all of their electrical resistance when cooled to super-low temperatures (near absolute zero, about -273o Celsius). It must be understood that superconductivity is not merely an extrapolation of most conductors’ tendency to gradually lose resistance with decreasing temperature; rather, it is a sudden, quantum leap in resistivity from finite to nothing. A superconducting material has absolutely zero electrical resistance, not just some small amount. Superconductivity was first di
• 12.8: Insulator Breakdown Voltage
The atoms in insulating materials have very tightly-bound electrons, resisting free electron flow very well. However, insulators cannot resist indefinite amounts of voltage. With enough voltage applied, any insulating material will eventually succumb to the electrical “pressure” and electron flow will occur. However, unlike the situation with conductors where current is in a linear proportion to applied voltage (given a fixed resistance), current through an insulator is quite nonlinear: for volt