9.3 Resistivity and Resistance

Copper wires are routinely used for extension cords and house wiring for several reasons. Copper has the highest electrical conductivity rating, and therefore the lowest resistivity rating, of all nonprecious metals. Also important is the tensile strength, where the tensile strength is a measure of the force required to pull an object to the point where it breaks. The tensile strength of a materia…

The resistance between the two conductors of a coaxial cable depends on the resistivity of the material separating the two conductors, the length of the cable and the inner and outer radius of the two conductor. If you are designing a coaxial cable, how does the resistance between the two conductors depend on these variables?

Do impurities in semiconducting materials listed in the table supply free charges? (Hint: Examine the range of resistivity for each and determine whether the pure semiconductor has the higher or lower conductivity.)

If aluminum and copper wires of the same length have the same resistance, which has the larger diameter? Why?

Calculate the effective resistance of a pocket calculator that has a 1.35-V battery and through which 0.200 mA flows.

What is the resistance of a 20.0-m-long piece of 12-gauge copper wire having a 2.053-mm diameter?

If the 0.100-mm-diameter tungsten filament in a light bulb is to have a resistance of $0.200 \Omega$ at $20.0 ° \text{C}$, how long should it be?

Find the ratio of the diameter of aluminum to copper wire, if they have the same resistance per unit length (as they might in household wiring).

(a) To what temperature must you raise a copper wire, originally at $20.0 ° \text{C}$, to double its resistance, neglecting any changes in dimensions? (b) Does this happen in household wiring under ordinary circumstances?

Of what material is a resistor made if its resistance is 40.0% greater at $100.0 ° \text{C}$ than at $20.0 ° \text{C}$?

(a) Of what material is a wire made, if it is 25.0 m long with a diameter of 0.100 mm and has a resistance of $77.7 \Omega$ at $20.0 ° \text{C}$? (b) What is its resistance at $150.0 ° \text{C}?$

A copper wire has a resistance of $0.500 \Omega$ at $20.0 ° \text{C} ,$ and an iron wire has a resistance of $0.525 \Omega$ at the same temperature. At what temperature are their resistances equal?