Thermal physics; lecture 6-7

Question 1

When does a phase change occur?

Answer 1

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

Question 2

how does evaporation cool our body

Answer 2

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

Question 3

How does condensation occur

Answer 3

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

Question 4

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!!

Answer 4

true (WOW)

Question 5

What is boiling

Answer 5

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

Question 6

What are the conditions of boiling

Answer 6

• pressure

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

Question 7

Define latent heat

Answer 7

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

Question 8

What does latent heat depend on

Answer 8

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

Question 9

latent heat of fusion

Answer 9

phase change from solid to liquid

Question 10

latent heat of vaporisation

Answer 10

liquid to gas

Question 11

What does heat of fusion mean?

Answer 11

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

heat fusion of water 344 J/g

Question 12

define heat of vaporization

Answer 12

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

Question 13

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

Answer 13

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

Question 14

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

Answer 14

true

Question 15

what causes atmospheric pressure

Answer 15

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

Question 16

What is the barometer

Answer 16

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

Question 17

What is an aneroid barometer

Answer 17

• 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

Question 18

what measures elevation

Answer 18

altmeter

Question 19

what is a manometer

Answer 19

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

Question 20

what does buoyant force mean

Answer 20

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

Question 21

buoyancy in air

Answer 21

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

Question 22

object lighter than air (rise or fall)

Answer 22

rise

Question 23

when does an object hover

Answer 23

weight of air displaced = the weight of the object

Question 24

When does a balloon stop rising

Answer 24

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

• the buoyant force on the balloon equals its weight

Question 25

what are the foundations of thermodynamics

Answer 25

conservation of energy | the fact that heat flows from hot to cold and not the other way round

Question 26

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

Answer 26

true

Question 27

what is absolute zero

Answer 27

when molecules have lost available kinetic energy

Question 28

what is internal energy

Answer 28

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

Question 29

if the gas expands (+ or - work)

Answer 29

the work done is positive

Question 30

if the volume compresses (work? + -)

Answer 30

negative

Question 31

volume remains constant

Answer 31

w= 0

Question 32

What does the first law of thermodynamics take into account

Answer 32

heat and work

Question 33

what does the first law of thermodynamics state?

Answer 33

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

Question 34

what is an isolated system

Answer 34

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

Question 35

What is an adiabatic process

Answer 35

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

Question 36

how is adiabatic conditions achieved

Answer 36

- 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

Question 37

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

Answer 37

true

Question 38

if gas is compressed adiabatically, work done is positive

Answer 38

true

Question 39

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

Answer 39

true

Question 40

What is absolute temperature based on

Answer 40

triple point | absolute zero