Thermal Physics lec 3-5

Question 1

Define linear thermal expansion

Answer 1

is the increase in size of an object with an increase in its temperature

• is the consquence of the change in the average between atoms in an object

Question 2

true or false; the amont of expansion is proportional to the initial length

Answer 2

true

Question 3

true or false; the fractional increase in length is proportional to the change in temperature

Answer 3

true

Question 4

What is a bimetallic strip

Answer 4

a strip of metal, who’s faces are made up of different metals; so that they have different average co- efficients of expansion (this can be used in thermostats)

Question 5

What is the area of expansion proportional to

Answer 5

the change in area is proportional to the original area and to the change in temperature

Question 6

What is volume of expansion proportional to

Answer 6

the change in volume is proportional to the orginal volume and to teh cahnge in temperature

Question 7

Beta is the coefficient of volume expansion (true or false)

Answer 7

true

Question 8

3alpha = beta for volume expansion

Answer 8

true

Question 9

What are the three main modes of heat transfer

Answer 9

conduction, convection, radiation

Question 10

In general what is conduction

Answer 10

the transfer of heat via the collision of particles (physical contact; matter does not move)

• it is an exchange of energy between microscopic particles by collisions

Question 11

In general what is convection

Answer 11

heat is transferred via macroscopic movement of matter (fluids)

Question 12

In general what is radiation

Answer 12

heat is transferred by electromagnetic waves that are emitted or absorbed

Question 13

what happens to a particle with less energy during a collision

Answer 13

it will gain energy; and become more energetic

Question 14

Why are metals good conductors?

Answer 14

• they contain large numbers of electrons taht are relatively free to move
• the can transport energy form one region to another

Question 15

What does it mean by a poor conductor

Answer 15

doesn’t transfer energy as efficiently between microscopic particles (good insulator)

Question 16

What does the rate of conduction depend on?

Answer 16

the characteristics of the substance

Question 17

What does the temperature gradient of a material measure delta T/ delta x

Answer 17

it measures the RATE at which temperature varies with position

Question 18

what does the proportionality constant k mean

Answer 18

the thermal conductivity of the substance

Question 19

What is heat flow measured in (rate of work)

Answer 19

Watts (W)

Question 20

true or false; good conductors have high k values

Answer 20

true

Question 21

true or false; good insulators have high k values

Answer 21

false; they have low k values; this is because k is the proportionality constant that represents the thermal conductivity of the substance

Question 22

true or false the larger the thermal conductivity of a substance the faster heat will be asbsorbed from our bodies

Answer 22

true

Question 23

Define thermal convection

Answer 23

energy transferred by movement of a substance

- is the flow of heat accompanying the flow of a fluid around an object

Question 24

What type of convection: when movement results from differences in density?

Answer 24

natural/ passive convection

Question 25

What type of convection: when movement is forced by a fan or a pump

Answer 25

forced convection

Question 26

in natural convection what causes the flow of the fluid

Answer 26

the flow of the heat

Question 27

in forced convection, what happens to the flow of heat?

Answer 27

the flow of heat is accelerated by rapid movement of cool fluid across the warm object

Question 28

in forced convection, what happens to the flow of heat?

Answer 28

the flow of heat is accelerated by rapid movement of cool fluid

Question 29

What does q symbolize

Answer 29

the coefficient of convective heat transfer

Question 30

What does q symbolize

Answer 30

...

Question 31

What does q depend on (object)?

Answer 31

the object: - shape - orientation

Question 32

What does q depend on (fluid)

Answer 32

fluid - density - specific heat capacity - thermal conductivity - viscosity

Question 33

Define radiation

Answer 33

exists as electromagnetic waves ranging from long (radio waves) to short wave lengths (x rays)

Question 34

What is the color of long waves

Answer 34

red

Question 35

What is the color a short wave

Answer 35

violet

Question 36

What is radiation (its temperature) measured in

Answer 36

kelvin

Question 37

What is terrestrial radiation

Answer 37

it comes from the earths' surface, in the form of infrared waves; below our threshold of sight

Question 38

What are conditions for the emission of radiant energy

Answer 38

- every object above absolute zero

Question 39

What type of radiation comes from the surface of the sun

Answer 39

solar radiation; electromagnetic radiation

Question 40

At room temperature; what is the emission?

Answer 40

infrared

Question 41

What is the color of the light above 500 C

Answer 41

red

Question 42

What is the color of light above 600C

Answer 42

yellow

Question 43

what is the color of light at 1500C

Answer 43

white

Question 44

What is a net absorber

Answer 44

absorbs more than it emits

Question 45

What is net emitter

Answer 45

emits more than in absorbs

Question 46

true or false; the net absorption is relative to temperature of surroundings

Answer 46

true

Question 47

a good absorber is good emitter?

Answer 47

true

Question 48

poor absorbers are poor emitters?

Answer 48

true

Question 49

Question: a hot pizza placed in the snow is a net emitter?

Answer 49

the net energy glow foes from higher to lower temperature. Since the pizza is hotter than the snow, emission is greater than absorption, so it's a net emitter

Question 50

What does reflection of radiant energy mean?

Answer 50

- opposite of absorption of radiant energy

Question 51

Why does Darkness occur?

Answer 51

eg. occurs in a closed box | - darkness is often due to the reflection of light back and forth many times partially absorbing with each reflection

Question 52

true or false; good reflectors are poor absorbers

Answer 52

true

Question 53

What is an ideal absorber

Answer 53

- defined as an object that absorbs all of the energy of the incident on it ; this object is called a black body

Question 54

what does 'e' stand for

Answer 54

emissivity; which is equal to absorptivity

Question 55

What is black body

Answer 55

absorbs all energy incident on it

Question 56

true or false; an ideal absorber is also an ideal radiator of energy

Answer 56

true

Question 57

what is an ideal reflector e=0

Answer 57

an ideal reflector absorbs NONE of the energy incident on it

Question 58

Which law do you use to measure the rate of energy transfer of a black body

Answer 58

Stefan's Law

Question 59

What happens when an object is in equilibrium with its surroundings

Answer 59

it radiates and absorbs at the same rate; and its temperature will not change

Question 60

what is emissivity

Answer 60

reduces the rate of emission

Question 61

What is light made of

Answer 61

electromagnetic waves

Question 62

true or false; the wavelength at which the maximum occurs is inversely proportional to the absolute temperature

Answer 62

true

Question 63

What is Dewar flask

Answer 63

- is a container designed to minimize the energy losses by conduction, convection and radiation - it is used to store either cold or hot liquids for long periods of time

Question 64

What causes the greenhouse effect

Answer 64

- energy absorbed from the sun, part re-radiated by the earth as longer wavelength terrestrial radiation

Question 65

What does transparency depend on?

Answer 65

the wavelength of an object

Question 66

What does it mean by terrestrial radiation

Answer 66

- absorbed by atmospheric gases and re-emitted as long wavelength terrestrial radiation back to Earth

Question 67

Newtons' Law of cooling

Answer 67

proportional to the temperature difference, delta T, between the object and its surroundings

Question 68

What is an example of Newton's Law of cooling

Answer 68

eg. Hot apple pie cools more each minute in a freezer than if left on the kitchen table (because their temperature difference is a lot)

Question 69

true or false; Newton's law of cooling also applies to warming

Answer 69

true; object cooler than its surroundings warms up at a rate proportional to change in T