Read Callister, Chapters 19 and 20. Solve and hand in Problems 19.12, 19.26, 19.D2, 20.2, 20.7, 20.10, 20.21, 20.28; due date Wednesday March 17.
Question 19.12
When a metal is heated its density decreases. This is for two reasons: thermal expansion of the solid; and the formation of vacancies. Consider a specimen of copper at 20 C with a density of 8940 kg/m3.
Question 19.26
Derive Equation 19.8
sigma = E * alphal * (T0-Tf)
from Equation 19.3:
(lf - l0)/l0 = alphal(T0-Tf)
Question 19.D2
The ends of a cylindrical rod 6.4 mm in diameter and 250 mm long are mounted between rigid supports. The rod is stress-free at 20 C, and can withstand a tensile stress of up to 138 MPa. If the rod has to survive being cooled to - 60 C, which of the following materials could it be made from: aluminium, copper, brass, 1025 steel, or tungsten?
Question 20.2
A coil of wire 0.1m long and having 15 turns carries a current of 1.0A.
Question 20.7
The magnetization within a bar of some metal alloy is 1.2 * 106 A/m at an H field of 200 A/m. Compute the magnetic susceptibility, permeability and magnetic flux density within the material. What types of magnetism are displayed by the material? What is the evidence for this?
Question 20.10
Consider a hypothetical metal having ferro-magnetic behaviour, a simple cubic crystal structure, an atomic radius of 0.125 nm, and a saturation flux density of 0.85 tesla. Find the number of Bohr magnetons per atom for this material.
Question 20.21
Schematically sketch on a single plot the B-H behaviour for a ferromagnetic material at 0 K, and at temperatures just below and just above its Curie temperature. Briefly explain why these curves have different shapes.
Question 20.28
An iron bar magnet having a coercivity of 4,000 A/m is to be demagnetised. If the bar is inserted in a cylindrical wire coil 0.15 m long and having 100 turns, what electric current is required to generate the necessary magnetic field?