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#### 1, (a) A 10-mm-diameter Brinell hardness indenter produced an indentation 1

###### Mechanical Engineering

1, (a) A 10-mm-diameter Brinell hardness indenter produced an indentation 1.62 mm in diameter in a steel alloy when a load of 500 kg was used. Compute the HB of this material.

(b) What will be the diameter of an indentation to yield a hardness of 450 HB when a 500 kg load is used?

1. 2.   Cite five factors that lead to scatter in measured material properties.

1. 3.    A large tower is to be supported by a series of steel wires. It is estimated that the load on eachwire will be 11,100 N (2500 lbf). Determine the minimum required wire diameter assuming a  factorof safety of 2 and a yield strength of 1030 MPa (150,000 psi).

1. 4.   (a) Compute the electrical conductivity of a 5.1-mm (0.2-in.) diameter cylindrical silicon specimen51 mm (2 in.) long in which a current of 0.1 A passes in an axial direction. A voltage of 12.5 V ismeasured across two probes that are separated by 38 mm (1.5 in.).

(b)  Compute the resistance over the entire 51 mm (2 in.) of the specimen.

1. 5.  In a semiconductor, what charge carriers are present?

1. 6.   To what temperature would 25 lbm of a 1025 steel specimen at 25°C (77°F) be raised if 125 Btu ofheat is supplied?

1. 7.    A 0.1 m (3.9 in.) rod of a metal elongates 0.2 mm (0.0079 in.) on heating from 20 to 100°C (68 to212°F). Determine the value of the linear coefficient of thermal expansion for this material.
1. 8.   (a) Explain the two sources of magnetic moments for electrons.

(b)  Do all electrons have a net magnetic moment? Why or why not?

(c)  Do all atoms have a net magnetic moment? Why or why not?

1. 9.   Briefly explain why metals are opaque to electromagnetic radiation having photon energies withinthe visible region of the spectrum.

1. 10.   Can a material have an index of refraction less than unity? Why or why not?

1. 11.     Briefly explain what determines the characteristic color of (a) a metal and (b) a transparentnonmetal.
• Posted: 4 years ago
• Due: 17/03/2016
• Budget: \$20