Mats Lecture 10

Question 1

Recall what the different types of energy are?

Answer 1

-Mechanical
-Chemical
-electrical
-Heat/thermal
-Nuclear
-Light/radiant

Question 2

Why is heat so important to material behaviour?

Answer 2

-Most processes require a certain amount of work to be done
-Heat usually provides most of the energy to do the work

Question 3

Describe what latent heat is

Answer 3

-the energy required for a phase change

Question 4

What is latent heat typically associated with?

Answer 4

-The change in entropy (randomness) of the atomic arrangement

Question 5

Describe what sensible heat is and why it is important

Answer 5

-the vibration of atoms
-At Absolute Zero (0k/-273 degrees Celsius), atoms in a solid begin to oscillate

Question 6

What is the Boltzmann constant?

Answer 6

-Kb
-is the proportionality factor that relates the average relative kinetic energy of particles in a gas with the thermodynamic temperature of the gas

Question 7

How is thermal energy stored in materials? relate this to a spring metaphor for bonds

Answer 7

-Atomic vibration stretches one spring and compresses the other

Question 8

When is energy at a max?

Answer 8

-When Δa is at a max

Question 9

When is energy at a min?

Answer 9

When Δa is equal to zero

Question 10

What is the definition of binding energy?

Answer 10

The minimum energy required to create or break a bond

Question 11

What is the definition of Heat Capacity?

Answer 11

-is a material property that characterizes the amount of energy required to increase the temperature of a given mass of that material

Question 12

What happens to materials when they are heated?

Answer 12

-They expand

Question 13

On an atomic level, what happens when atoms are heated?

Answer 13

-The amplitude of atomic vibrations increases when atoms are heated
-The atoms vibrate about an increasing mean spacing

Question 14

What do stronger bonds mean graphically?

Answer 14

-A steeper force-spacing curve
-a deeper energy well meaning less expansion (a lower CTE)

Question 15

What do stronger bonds imply?

Answer 15

-Higher Young’s Modulus
-Higher Melting Temperature

Question 16

Define what Thermal Conductivity means

Answer 16

-The rate at which heat is conducted through a solid under steady state conditions

Question 17

List the ways that heat is transmitted through solids

Answer 17

1. Thermal Vibrations (all materials)
2. The motion of free electrons (metals)
3. Radiation (transparent materials)

Question 18

What are thermal vibrations also known as?

Answer 18

phonons

Question 19

what are thermal vibrations?

Answer 19

-are elastic waves that travel at the speed of sound

Question 20

What is thermal diffusivity?

Answer 20

-Heat flow in transient conditions (temperature that changes with time)

Question 21

How is thermal diffusivity measured?

Answer 21

-By subjecting one end of a material to a heat pulse (aka by a laser) and measuring the TIME it takes for the temperature rise to be sensed at the other end

Question 22

What does thermal expansion depend on?

Answer 22

-on the strength and stiffness of the atomic bonds

Question 23

How can you manipulate the volumetric Heat Capacity of a material?

Answer 23

-Foaming (reducing the density) is the only approach
-volumetric Heat Capacity is constant for all materials