A potential difference of $12.0 \mathrm{~V}$ is applied across a wire of crosssectional area $4.50 \mathrm{~mm}^2$ and length 1000 . km. The current passing through the wire is $3.20 \cdot 10^{-3} \mathrm{~A}$. b) What type of wire is this?

The most common material used for sandpaper, silicon carbide, is also widely used in electrical applications. On common device is a tubular resistor made of a special grade of silicon carbide called carborundum. A particular carborundum resistor (see the figure) consists of a thick-walled cylindrical shell (a pipe) of inner radius $a=1.50 \mathrm{~cm}$, outer radius $b=2.50 \mathrm{~cm}$, and length $L=60.0 \mathrm{~cm}$. The resistance of this carborundum resistor at $20.0^{\circ} \mathrm{C}$ is $1.00 \Omega$. b) Carborundum has a high temperature coefficient of resistivity: $\alpha=2.14 \cdot 10^{-3} \mathrm{~K}^{-1}$. If, in a particular application, the carborundum resistor heats up to $300 .{ }^{\circ} \mathrm{C}$, what is the percentage change in its resistance between room temperature $\left(20.0^{\circ} \mathrm{C}\right)$ and this operating temperature?

The most common material used for sandpaper,silicon carbide,is also widely used in electrical applications. Onecommon device is a tubular resistor made of a special grade of silicon carbide called carborundum. A particular carborundum resistor (see the figure) consists of a thick-walled cylindrical shell (a pipe) of inner radius $a=1.50 \mathrm{~cm}$, outer radius $b=2.50 \mathrm{~cm}$, and length $L=60.0 \mathrm{~cm}$. The resistance of this carborundum resistor at $20.0^{\circ} \mathrm{C}$ is $1.00 \Omega$. a) Calculate the resistivity of carborundum at room temperature. Compare this to the resistivities of the most commonly used conductors (copper, aluminum, and silver).

A copper wire that is $1.00 \mathrm{~m}$ long and has a radius of $0.500 \mathrm{~mm}$ is stretched to a length of $2.00 \mathrm{~m}$. What is the fractional change in resistance, $\Delta R / R$, as the wire is stretched? What is $\Delta R / R$ for a wire of the same initial dimensions made out of aluminum?

A rectangular wafer of pure silicon, with resistivity $\rho=2300 \Omega \mathrm{m}$, measures $2.00 \mathrm{~cm}$ by $3.00 \mathrm{~cm}$ by $0.0100 \mathrm{~cm}$. Find the maximum resistance of this rectangular wafer between any two faces.

What gauge of aluminum wire will have the same resistance per unit length as 12-gauge copper wire?