Chapter 6

What will be the resistance of a copper wire \(0.08\) in. in diameter and \(100 \mathrm{ft}\) long if its resistivity is \(1.7 \mu \Omega \cdot \mathrm{cm}\) ?

Silicon has a density of \(2.40 \mathrm{~g} / \mathrm{cm}^{3}\). (a) What is the concentration of the silicon atoms per cubic centimeter? (b) Phosphorus is added to the silicon to make it an \(n\)-type semiconductor with a conductivity of \(1 \mathrm{mho} / \mathrm{cm}\) and an electron mobility of \(1700 \mathrm{~cm}^{2} / \mathrm{V}-\mathrm{s}\). What is the concentration of the conduction electrons per cubic centimeter?

Calculate the mobility of electrons in \(\mathrm{Cu}\). The resistivity of \(\mathrm{Cu}\) is \(1.72 \times\) \(10^{-8} \Omega \cdot \mathrm{m}\) at \(25^{\circ} \mathrm{C}\) and its density is \(8.9 \mathrm{~g} / \mathrm{cm}^{3}\). Assume each copper atom donates one valence electron to the conduction band.

A coil of wire \(0.1 \mathrm{~m}\) long and having 15 turns carries a current of \(1.0 \mathrm{~A}\). (a) Compute the magnetic induction if the coil is within a vacuum. (b) A bar of molybdenum is now placed in the coil, and the current adjusted to maintain the same magnetic induction as in part (a). Calculate the magnetization.

Look up the refractive indices for fused silica and dense flint glass, and calculate the ratio of their reflectivities. Cite the source of your information.