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Physics > Thermal physics; lecture 6-7 > Flashcards

Thermal physics; lecture 6-7 Flashcards

1
Q

When does a phase change occur?

A

when the heat added to a substance increases the temperature of the substance enough that, it reaches a temperature that is characteristic for a phase change

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2
Q

how does evaporation cool our body

A

water on our skin absorbs body heat, as evaporation cools the body

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3
Q

How does condensation occur

A

gas to liquid
- gas molecules near a liquid surface are attracted to the liquid; they strike the surface with increased KE becoming part of the liquid

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4
Q

true or false; if enough energy is supplied to a vapor the molecules or atoms will disintegrate into ions and electrons, form plasma of charged particles = 4th phase of matter!!

A

true (WOW)

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5
Q

What is boiling

A

rapid evaporation from beneath the surface of a liquid; forms vapor bubbles beneath the surface

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6
Q

What are the conditions of boiling

A
  • pressure

- altitude (boiling point is lower with lower atmospheric pressure)

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7
Q

Define latent heat

A

the heat needed for 1 kg of substance to undergo phase change

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8
Q

What does latent heat depend on

A

the material, also on the phase change about to occur on the substance

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9
Q

latent heat of fusion

A

phase change from solid to liquid

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10
Q

latent heat of vaporisation

A

liquid to gas

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11
Q

What does heat of fusion mean?

A

amount of energy needed to change any substance from solid to liquid

heat fusion of water 344 J/g

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12
Q

define heat of vaporization

A

amount of energy needed to change any substance from liquid to gas; and vice versa

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13
Q

What is the only stress that can be exerted on an object submerged in a static fluid

A

is the one that tends to compress the object from all sides

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14
Q

true or false; the force exerted by a static fluid on an object is always perpendicular to the surfaces of the object

A

true

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15
Q

what causes atmospheric pressure

A
  • caused by weight of air
  • varies from one locality to another
  • not uniform
  • measurements are used to predict weather conditions
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16
Q

What is the barometer

A

it is a device used to measure atmospheric pressure
- it consists of a mercury tube, upside down and a dish filled with mercury; the height of the mercury column tells us the atmospheric pressure

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17
Q

What is an aneroid barometer

A
  • partially exhausted metal box of air with a flexible
  • lid bends in and out with changes in atmospheric pressure
  • the motion of the lid is indicated on a scale
18
Q

what measures elevation

A

altmeter

19
Q

what is a manometer

A
  • a device used to measure the pressure of a gas contained in a vessel
20
Q

what does buoyant force mean

A

the upward force exerted by the fluid on any immersed object

  • the buoyant force is the resultant force due to all forces applied by the fluid of surrounding the parcel
21
Q

buoyancy in air

A

archimedes principle: states that an object surrounded by air is buoyed up by a force equal to the weight of displaced air

22
Q

object lighter than air (rise or fall)

A

rise

23
Q

when does an object hover

A

weight of air displaced = the weight of the object

24
Q

When does a balloon stop rising

A

when the weight of the displaced air equals the total weight of the balloon

  • the buoyant force on the balloon equals its weight
25
Q

what are the foundations of thermodynamics

A

conservation of energy

the fact that heat flows from hot to cold and not the other way round

26
Q

true or false; at zero degrees with pressure constant, volume changes by 1/273 for each degree celsius

A

true

27
Q

what is absolute zero

A

when molecules have lost available kinetic energy

28
Q

what is internal energy

A

energy at the particle level within a substance in several forms
- simplest form is PE and KE

29
Q

if the gas expands (+ or - work)

A

the work done is positive

30
Q

if the volume compresses (work? + -)

A

negative

31
Q

volume remains constant

A

w= 0

32
Q

What does the first law of thermodynamics take into account

A

heat and work

33
Q

what does the first law of thermodynamics state?

A

the heat added to system transforms into an equal amount of some other form of energy

34
Q

what is an isolated system

A

one that does not interact with its surroundings
- no energy transfer by heat takes place
- the work done on the system is zero
the internal energy remains constant

35
Q

What is an adiabatic process

A

compressing or expanding gas while no heat enters or leaves the system

36
Q

how is adiabatic conditions achieved

A
  • thermally insulated system from its surroundings

- performing the process so rapidly that heat has no time to enter or leave change in e internal = work

37
Q

true or false if the gas expands adiabatically, work is negative

A

true

38
Q

if gas is compressed adiabatically, work done is positive

A

true

39
Q

true or false; when an object floats; the fraction of the volume of floating object that is below the fluid surface is equal to the ratio of the density of the object to that fluid

A

true

40
Q

What is absolute temperature based on

A

triple point

absolute zero

Physics (7 decks)

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