Physical Properties of Materials Flashcards
Define density as a material property
. Density is the weight per unit volume of a material.
What is the difference in melting characteristics between a pure metal element and a metal alloy?
A pure metal element melts at one temperature (the melting point), while most metal alloys begin melting at a certain temperature called the solidus and finally completes the transformation to the molten state at a higher temperature called the liquidus. Between the solidus and liquidus, the alloy is a mixture of solid and liquid.
Describe the melting characteristics of a noncrystalline material such as glass.
In the heating of a noncrystalline material such as glass, the material begins to soften as temperature increases, finally converting to a liquid at a temperature defined for the material as the melting point.
Define specific heat as a material property.
Specific heat is defined as the quantity of heat required to raise the temperature of a unit mass of the material by one degree.
What is thermal conductivity as a material property?
Thermal conductivity is the capacity of a material to transfer heat energy through itself by thermal movement only (no mass transfer).
Define thermal diffusivity.
Thermal diffusivity is thermal conductivity divided by volumetric specific heat.
What are the important variables that affect mass diffusion?
According to Fick’s first law, mass diffusion depends on the diffusion coefficient of the material, which increases rapidly with temperature (so temperature could be listed as an important variable), concentration gradient, contact area, and time.
Define resistivity as a material property.
Resistivity is the material’s capacity to resist the flow of electric current
Why are metals better conductors of electricity than ceramics and polymers?
Metals are better conductors because of metallic bonding, which permits electrons to move easily within the metal. Ceramics and polymers have covalent and ionic bonding, in which the electrons are tightly bound to particular molecules.
What is dielectric strength as a material property?
Dielectric strength is defined as the electrical potential required to break down the
insulator per unit thickness.
What is an electrolyte?
An electrolyte is an ionized solution capable of conducting electric current by movement of the ions.
Determine the length and width of a rectangular nickel plate whose room
temperature (20C) dimensions are 300 mm by 400 mm by 5 mm, if the plate is heated to
250C.
- 918 mm
401. 224 mm
(SI units) A bridge to be fabricated of steel girders is designed to be 500 m long and 12 m
wide at ambient temperature (assumed 20°C). Expansion joints will be provided to
compensate for the change in length in the girders as the temperature varies. Each expansion
joint can compensate for a maximum of 20 mm of change in length. From historical records
it is estimated that the minimum and maximum temperatures in the region will be -35°C and
40°C, respectively. Determine (a) the minimum number of expansion joints required and (b)
the length that each bridge section should be fabricated.
Therefore, a minimum of 23 joints are needed for the total bridge length.
(b) If there are 23 joints separating adjacent sections of the bridge, then there must be 24
bridge sections to be fabricated. Each bridge section will be 500/24 = 20.833 m long at 20°C.
Determine the amount of heat required to increase the temperature of an aluminum
block that is 10 cm by 10 cm by 10 cm from room temperature (21C) to 300C.
158,193 cal
662,196 J
A 16 gage copper wire (0.0508-in diameter) connects a solenoid to a
control circuit that is 50 ft away. (a) What is the resistance of the wire? (b) If a current was
passed through the wire, it would heat up. How does this affect the resistance?
0.198 ohms
If a current is passed through the wire causing the wire to heat up, the resistivity of the
wire would change. Since nickel is a metal, the resistivity would increase, causing the
resistance to increase. This, in turn, would cause slightly more heat to be generated.
