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Physics > Thermal Physics lec 3-5 > Flashcards

Thermal Physics lec 3-5 Flashcards

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1
Q

Define linear thermal expansion

A

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
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2
Q

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

A

true

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3
Q

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

A

true

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4
Q

What is a bimetallic strip

A

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)

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5
Q

What is the area of expansion proportional to

A

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

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6
Q

What is volume of expansion proportional to

A

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

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7
Q

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

A

true

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8
Q

3alpha = beta for volume expansion

A

true

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9
Q

What are the three main modes of heat transfer

A

conduction, convection, radiation

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10
Q

In general what is conduction

A

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
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11
Q

In general what is convection

A

heat is transferred via macroscopic movement of matter (fluids)

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12
Q

In general what is radiation

A

heat is transferred by electromagnetic waves that are emitted or absorbed

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13
Q

what happens to a particle with less energy during a collision

A

it will gain energy; and become more energetic

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14
Q

Why are metals good conductors?

A
  • they contain large numbers of electrons taht are relatively free to move
  • the can transport energy form one region to another
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15
Q

What does it mean by a poor conductor

A

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

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16
Q

What does the rate of conduction depend on?

A

the characteristics of the substance

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17
Q

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

A

it measures the RATE at which temperature varies with position

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18
Q

what does the proportionality constant k mean

A

the thermal conductivity of the substance

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19
Q

What is heat flow measured in (rate of work)

A

Watts (W)

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20
Q

true or false; good conductors have high k values

A

true

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21
Q

true or false; good insulators have high k values

A

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

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22
Q

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

A

true

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23
Q

Define thermal convection

A

energy transferred by movement of a substance

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

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24
Q

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

A

natural/ passive convection

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25
Q

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

A

forced convection

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26
Q

in natural convection what causes the flow of the fluid

A

the flow of the heat

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27
Q

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

A

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

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28
Q

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

A

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

29
Q

What does q symbolize

A

the coefficient of convective heat transfer

30
Q

What does q symbolize

A

…

31
Q

What does q depend on (object)?

A

the object:

  • shape
  • orientation
32
Q

What does q depend on (fluid)

A

fluid

  • density
  • specific heat capacity
  • thermal conductivity
  • viscosity
33
Q

Define radiation

A

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

34
Q

What is the color of long waves

A

red

35
Q

What is the color a short wave

A

violet

36
Q

What is radiation (its temperature) measured in

A

kelvin

37
Q

What is terrestrial radiation

A

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

38
Q

What are conditions for the emission of radiant energy

A
  • every object above absolute zero
39
Q

What type of radiation comes from the surface of the sun

A

solar radiation; electromagnetic radiation

40
Q

At room temperature; what is the emission?

A

infrared

41
Q

What is the color of the light above 500 C

A

red

42
Q

What is the color of light above 600C

A

yellow

43
Q

what is the color of light at 1500C

A

white

44
Q

What is a net absorber

A

absorbs more than it emits

45
Q

What is net emitter

A

emits more than in absorbs

46
Q

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

A

true

47
Q

a good absorber is good emitter?

A

true

48
Q

poor absorbers are poor emitters?

A

true

49
Q

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

A

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

50
Q

What does reflection of radiant energy mean?

A
  • opposite of absorption of radiant energy
51
Q

Why does Darkness occur?

A

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

52
Q

true or false; good reflectors are poor absorbers

A

true

53
Q

What is an ideal absorber

A
  • defined as an object that absorbs all of the energy of the incident on it ; this object is called a black body
54
Q

what does ‘e’ stand for

A

emissivity; which is equal to absorptivity

55
Q

What is black body

A

absorbs all energy incident on it

56
Q

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

A

true

57
Q

what is an ideal reflector e=0

A

an ideal reflector absorbs NONE of the energy incident on it

58
Q

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

A

Stefan’s Law

59
Q

What happens when an object is in equilibrium with its surroundings

A

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

60
Q

what is emissivity

A

reduces the rate of emission

61
Q

What is light made of

A

electromagnetic waves

62
Q

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

A

true

63
Q

What is Dewar flask

A
  • 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
64
Q

What causes the greenhouse effect

A
  • energy absorbed from the sun, part re-radiated by the earth as longer wavelength terrestrial radiation
65
Q

What does transparency depend on?

A

the wavelength of an object

66
Q

What does it mean by terrestrial radiation

A
  • absorbed by atmospheric gases and re-emitted as long wavelength terrestrial radiation back to Earth
67
Q

Newtons’ Law of cooling

A

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

68
Q

What is an example of Newton’s Law of cooling

A

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)

69
Q

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

A

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

Physics (7 decks)

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