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MED 101- PHYSICS I > 12. THERMODYNAMICS II > Flashcards

12. THERMODYNAMICS II Flashcards

1
Q
  1. What are the three physical states that matter exists in?
A
  • solid
  • liquid
  • vapor
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2
Q
  1. What can change about a material when it absorbs heat?
A
  • its physical state
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3
Q
  1. What is Melting?

Give an example.

A
  • it is when a solid changes from the solid state
  • to the liquid state
  • the process requires energy
  • this is because the molecules of a solid are found in a rigid structure
  • they are not free to move without added energy
  • EG: melting an ice cube to form liquid water
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4
Q
  1. What is Freezing?
A
  • it is when a liquid is frozen to form a solid
  • it is the reverse of melting
  • it requires energy to be removed from the liquid
  • this is so that the molecule can settle into a rigid structure
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5
Q
  1. What is Vaporizing?

Give an example.

A
  • it is changing a substance from its liquid state to its vapour (gas) state
  • this process requires energy
  • this is because the molecules must be freed from their clusters
  • boiling liquid water
  • this transforms it to water vapour (or steam)
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6
Q
  1. What is steam?
A
  • it is the gas of individual water molecules
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7
Q
  1. What is Condensing?
A
  • it is when a gas is condensed to form a liquid
  • it is the reverse of vaporizing
  • it requires energy to be removed from the gas
  • this allows the molecules of the gas to cluster instead of flying away from one another
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8
Q
  1. What is a material’s heat of transformation?
    What is another word for the heat of the transformation?
A
  • it is the amount of energy required per unit mass
  • to change the state of a particular material
  • it does NOT change the temperature
  • the Latent Heat
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9
Q
  1. What is the symbol for heat of transformation?
A
  • L
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10
Q
  1. What is the formula to work out the heat of the transformation?
A

Q= L x m

  • Q= the measure of the heat energy (J/kg)
  • L= constant
    = it is the latent heat dependent on the material
    = it is measured in joules
  • m = mass (kg)
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11
Q
  1. What is the Heat of Vaporization (Lv)?
A
  • it is the amount of energy per unit mass
  • that must be added to vaporize a liquid
  • OR that must be removed to condense a gas
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12
Q
  1. What is the Heat of Fusion (Lf)?
A
  • it is the amount of energy per unit mass
  • that must be added to melt a solid
  • OR that must be removed to freeze a liquid
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13
Q
  1. Why is an effective mode of body heat loss important?
A
  • all our metabolism goes into making heat
  • very little of our metabolism goes into useful mechanical work
  • our body temperature would rise very quickly if we did not have effective modes of heat loss
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14
Q
  1. What are the five modes of heat loss?
A
  1. Radiation
  2. Convection
  3. Conduction
  4. Evaporation of sweat
  5. Evaporation of water through breathing
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15
Q
  1. What is radiation loss?

What percentage of heat is lost through this?

A
  • it is the loss of heat by the emission of electromagnetic radiation
  • 54%-60% heat loss
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16
Q
  1. What is convection?

What percentage of heat is lost through this?

A
  • the loss of radiated heat
  • it is removed by moving air
  • around 25% of heat is lost
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17
Q
  1. What is conduction?

What percentage of heat is lost through this?

A
  • it is the direct transfer of heat through contact
  • around 25% of heat is lost
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18
Q
  1. What is the Evaporation of sweat?

What percentage of heat is lost through this?

A
  • it is the loss of heat by the evaporation of water
  • around 7% of heat is lost
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19
Q
  1. What is the Evaporation of water through breathing?

What percentage of heat is lost through this?

A
  • it is the loss of heat by the evaporation of water
  • around 14% of heat is lost
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20
Q
  1. What do the magnitude and importance of the four modes of heat loss depend on?
A
  • clothing
  • environment
  • surroundings
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21
Q
  1. What is thermal radiation?
A
  • it is the exchange of energy as heat between an object and its environment
  • this is done via electromagnetic waves
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22
Q
  1. What happens when you stand near a fire?
A
  • you are warmed
  • you absorb the thermal radiation from the fire
  • your thermal energy increases as the fire’s thermal energy decreases
  • there is no medium required for the heat transfer via radiation
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23
Q
  1. Why is there no medium required for heat transfer that is accomplished through radiation?
A
  • radiation can travel through a vacuum
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24
Q
  1. According to Planck’s Law, what do all objects at a temperature (T) emit?
A
  • they emit Thermal radiation
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25
Q
  1. What is essential in Planck’s law?
A
  • the presence of a black body
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26
Q
  1. What is a Black Body?
    List three characteristics.
A
  1. It is a body that absorbs all the thermal radiation falling onto it
  2. At thermal equilibrium, it emits as much energy as it absorbs
  3. It is a good absorber of radiation
    and a good emitter of radiation
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27
Q
  1. What is Radiation incident?
A
  • the unintended exposure of an individual to radiation
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28
Q
  1. What are the three types/components of Radiation Incident?
A
  • reflection of the radiation by the object
  • absorption of the radiation into the object
  • transmission of radiation through the object
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29
Q
  1. What is Emissivity?
A
  • it is the fraction of the energy incident on the object
    that is absorbed
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30
Q
  1. What can be said about the Emissivity of a shiny, metallic, reflective surface?
A
  • it is very low
  • less than 0.1

NB: emissivity exists on a scale from 0 to 1

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31
Q
  1. What can be said about the Emissivity of dull, black surfaces?
A
  • they have the highest emissivity
  • between 0.9 and 1
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32
Q
  1. What is the unit for Emissivity?
A
  • ε
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33
Q
  1. What is the formula to calculate emissivity?
A

P = 𝑒. σ . A . T⁴

  • P= the radiated power (Watts)
  • 𝑒 = emissivity
    = it is a ratio
    = it has no units
  • σ= the Stefan - Boltzman Constant
    = 5.67 x 10 ⎺⁸ (W/m².K⁴)
  • A = the surface area (m²)
  • T = the temperature (Kelvins)
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34
Q
  1. What does the Stefan Boltzman Law represent?

How can this be expressed in a formula?

A
  • the energy per second (power) radiated by the surface
  • ▵Q / ▵t
35
Q
  1. Where does the body receive radiant energy from?
A
  • the surrounding objects
36
Q
  1. What unit of measurement can we find to calculate the approximate difference between the energy radiated by the body AND the energy absorbed from the radiation from the surroundings?
A
  • we can look for Hr
  • this is the rate of energy loss or gain
  • it is another way of writing power
  • it is measured in watts
37
Q
  1. What is the formula for Hr?
A
  • Hr = Power (watts)
  • Kr = constant
    = it is a parameter
    = it is about 2.1 x 10⁴ (J/m²hr°C)
    = it can also be written as 5.0 kcal/m²hr°C
  • Ar = the effective body surface area (m²)
    = it is what is emitting the radiation
  • 𝑒 = surface emissivity
  • (Ts - Tw) = difference in temperature
    = this can be in any unit
  • Ts = the skin temperature (°C)
  • Tw = the surrounding walls temperature (°C)
38
Q
  1. When does Conduction occur?
A
  • when the thermal energy moves through a material as a result of collisions
  • these collisions happen between free electrons, ions, atoms and molecules of the material
39
Q
  1. What can be said about the average kinetic energy of a hotter substance?
A
  • it is higher
40
Q
  1. What happens with regards to energy between materials in contact with one another?
A
  • the higher energy atoms in the warmer substances transfer energy to the lower energy atoms in the cooler substances
  • this is a result of atomic collisions between the two
  • this allows heat to flow from hot to cold
41
Q
  1. How would we calculate the temperature difference?
A

▵T = T1 - T 2

42
Q
  1. What is the temperature gradient?
A
  • the ▵T / ▵ x
  • ▵T = the change in temperature
    = the unit is not important
  • ▵x = the thickness of the body
  • this is the rate of change of temperature with distance
43
Q
  1. How would we work out the quantity of heat (▵Q) that is transmitted from Face 1 to Face 2 of the body for a given time (▵t)?
A

▵Q / ▵t = kT x A x ▵T/▵x

kT= this is the thermal conductivity of the material
= this depends on the material of the body
= it has a unit of W/m.K

A= the cross sectional area (m²)

▵T = the change in temperature
= the unit is not important

▵x = thickness
= change in distance (m)

44
Q
  1. What is another way of working out ▵Q / ▵t?
A

▵Q / ▵t = h x A x ▵T

  • h = the coefficient of the conduction heat transfer
  • A = the cross sectional area (m²)
  • ▵T = change in temperature
    = the unit is not important
45
Q
  1. How else can we calculate the coefficient of conduction heat transfer (h)?
A

h = kT / ▵x

  • kT= the thermal conductivity
    = W/m.K.
  • ▵x= thickness of the body
    = the distance (m)
46
Q
  1. What is the flame of a candle classified as?
A
  • it is convection
  • it is this convection that is transporting the thermal energy upwards
  • this energy transfer occurs when:
    • a fluid (air)
    • encounters an object (match)
    • with a higher temperature than that of the fluid

-the temperature of the part of the fluid that is in contact with the hot object increases

  • the fluid expands
  • it becomes less dense
  • it is now lighter than the surrounding cooler fluid
  • buoyant forces cause it to then rise
47
Q
  1. How can the heat loss due to Convection/Conduction be worked out?
A
  • we must find the heat loss due to convection (Hc)
  • this is the rate of energy transfer
  • it is another way of working out power
  • it has a unit of Watts
48
Q
  1. What is the formula for working out Hc?
A

Hc = Kc x Ac x (Ts - Ta)

  • Hc = the heat loss due to convection
    = power (in watts)
  • Kc = a parameter
    = it depends on the movement of the air
      = when the speed of the air is less than 0.2 m/s
  = it then has a value of 3.1 W/m²K
  • Ac = the effective body surface area (m²)
  • Ts = the skin temperature in Kelvins
  • Ta = the air temperature in Kelvins
49
Q
  1. When is the Convective heat loss greater?
A
  • when the air is moving
  • the Convective heat loss is much smaller when the air is still
50
Q
  1. What is Convection within the body called?
A
  • the flow of blood
51
Q
  1. What does the flow of blood change?
    What does it not affect?
A
  • it changes the distribution of the temperature within the body
  • it does not affect the average temperature of the body
52
Q
  1. What is the normal core body temperature?
A
  • 36.5° - 37.5°
53
Q
  1. How much does the core temperature generally change during the waking hours?
A
  • it increases by 0.5 ° C
54
Q
  1. What is an example of how well the body controls its temperature?
A
  • the nude body can maintain its core temperature (between 36°C and 38°C) for several hours
  • it can do this within environmental temperature changes that range from 21°C and 54°C in dry air
55
Q
  1. What is the correlation between temperature deviation from the normal body temperature, and exposure time?
A
  • the larger the temperature deviation from the normal body temperature
  • the shorter the maximum possible exposure time until death
56
Q
  1. What is the Convection Temperature for a naked adult man as compared to a naked baby?
    (if we have minimal air movement)
A
  • naked adult man = 26°C
  • naked baby = 35°C
57
Q
  1. Where is the Thermoneutral Zone located?
    (the zone of minimal metabolism)
A
  • it is between the Tc (Convection Temperature)
    AND
  • the Th (Hypothermia Temperature)
58
Q
  1. What happens below the Tc (convection temperature)?
A
  • the heat loss increases
  • this is due to convection and radiation
59
Q
  1. What increases metabolism?
A
  • increases in muscle tension
  • shivering
60
Q
  1. What increases muscle tension and shivering?
A
  • increases in the difference between the body temperature and the environmental temperatures
61
Q
  1. What happens to the core body temperature at low temperatures?
A
  • it cannot be maintained
  • there is cooling
  • hypothermia develops
62
Q
  1. How does heat loss happen above Th
    (Hypothermia Temperature)?
A
  • it is dominated by evaporation
63
Q
  1. Give the core temperature ranges for each of the following:

63.1: Mild Hypothermia
63.2: Moderate Hypothermia
63.3: Severe Hypothermia

A

63.1: 32°C- 35°C

63.2: 28°C - 32°C

63.3: less than 28°C

64
Q
  1. Which temperature is usually lower than the Core
    temperature (37°C)?
A
  • the temperature of the body skin (Tskin)
  • this usually sits at 34°C
65
Q
  1. What is Thermoregulation?
A
  • it is the maintenance of a constant core body temperature in an organism
  • both humans and other warm-blooded organisms thermoregulate
66
Q
  1. What is the term given to warm-blooded organisms?
A
  • homeotherms
67
Q
  1. What aspects of the human body allow it to thermoregulate?
A
  • the human body has temperature-sensitive receptors
  • these are located in the skin, hypothalamus, midbrain, spinal cord and the abdominal cavity
  • these thermoreceptors sense either hot and cold
  • most areas of the human body have both kinds of thermoreceptors
  • the sensors send information to the hypothalamus in the brain
  • this controls the body’s response to the stimuli
68
Q
  1. How do the blood vessels in the body react when the internal body temperature or the skin temperature gets too low?
A
  • these blood vessels are found adjacent to the skin
  • the blood vessel becomes smaller
  • it constricts
  • it reduces the blood flow from the core to the surface
  • this process is called Vasoconstriction
69
Q
  1. What are the effects of Vasoconstriction?
A
  • it reduces the rate of heat loss from the skin surface
  • it allows the skin to get colder
70
Q
  1. What is Vasodilation and when is it used?
A
  • it is when the blood vessel increases in size
  • it expands
  • this happens when there is a need to increase the rate of heat loss
  • this happens when the body is too hot
  • the blood supply to the skin is increased by Vasodilation
  • this increases the blood flow in the skin
  • this reduces the blood pressure
71
Q
  1. What is Piloerection?
A
  • it is when the fine body hairs stand on end
  • this is an attempt to reduce convective heat loss from the skin
  • the raising of the air is intended to create a stationary layer of air between the skin and the surroundings
72
Q
  1. What is Shivering?
A
  • it is a physiological response to cold temperatures
  • cold signals are transmitted to the hypothalamus
  • they trigger the reflex
  • the body muscles begin to make small movements to use up some metabolic energy
  • this generates thermal energy
73
Q
  1. What is Perspiration/ Sweating?
A
  • it is a very effective cooling mechanism
  • this is because the Latent Heat (L) of evaporation of water is high
  • heat loss that is caused by the evaporation of the liquid from the skin is the only way we can lose heat when the air is above 37°C
  • the human body has sweat glands in the skin
  • these excrete fluid
  • it is mainly water
  • it has some dissolved salts in it
74
Q
  1. Read through this summary.
    Does everything make sense?
75
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    Does everything make sense?
76
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    Does everything make sense?
77
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78
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    Does everything make sense?
79
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80
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81
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82
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    Does everything make sense?
83
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    Does everything make sense?
84
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    Does everything make sense?

MED 101- PHYSICS I (28 decks)

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