Homework 6 Flashcards
How do you estimate the energy required to raise the temperature
E=c_pm(T2-T1)
explain why Cv rises with increasing temperature at temperatures near 0 K
As temperature increases, more of the lattice waves may be excited by the available thermal energy, and, hence, the ability of the solid to absorb energy (i.e., the magnitude of the heat capacity) increases.
explain why Cv becomes virtually independent of temperature at temperatures
far removed from 0 K
all of the lattice waves have been excited and the energy required to produce an
incremental temperature change is nearly constant
steady-state heat flux through a plate? How do you find total heat loss
Equation 19.5 use Kelvins. dQ/dt=qAt
Briefly explain why metals are typically better thermal conductors than ceramic material
for metals, most of the heat is transported by free electrons.
ceramic materials, the primary mode of thermal conduction is via phonons, and phonons are more easily scattered than are free electrons.
Briefly explain why thermal stresses may be introduced into a structure by rapid
heating or cooling
temperature gradients are established across the cross section due to more rapid
temperature changes at the surface than within the interior; thus, the surface will expand or
contract at a different rate than the interior and since this surface expansion or contraction will be
restrained by the interior, stresses will be introduced
For cooling, what is the nature of the surface stresses
the surface stresses will be tensile in nature since the interior contracts to
a lesser degree than the cooler surface
For heating, what is the nature of the surface stresses
For heating, the surface stresses will be compressive in nature since the interior
expands to a lesser degree than the hotter surface
magnitude of the stress of a rod?
Equation 19.8, E: Modulus of Elasticity
is stress independent of rod length?
True
