9 — Thermal processes

Question 1

Thermal equilibrium

Answer 1

Thermal equilibrium describes a state in which 2 or more subjects hv the same tempt n there is no net transfer of energy betw them.

Question 2

Conduction

Answer 2

Conduction is a process of energy transfer where energy is transferred thru the passing on of vibrational motion from one particle to another without any flow of the material medium.

Question 3

Good thermal conductors

Answer 3

R materials that can transfer energy quickly by conduction

Question 4

Thermal insulators

Answer 4

R materials that transfer energy slow by conduction

Question 5

Convection

Answer 5

is a process of energy transfer by means of convection currents of a fluid (liquid or gas) due to a difference in density

Question 6

Radiation

Answer 6

Is the process of energy transfer by electromagnetic waves. It does not require a medium.

Question 7

Applications of conduction in non-metals

Answer 7

Hairdryers, instant water heaters, thermal wear, double glazed windows

Question 8

Applications of convection

Answer 8

Electric kettles, hot air balloons, sea breeze, land breeze

Question 9

Applications of radiation

Answer 9

Greenhouses, space blankets

Question 10

Energy transfer answer formula

Answer 10

X at a higher tempt than y. Energy is transferred from x to y. As energy in internal store of x decreases, tempt of x decreases and energy in internal store of y increases, tempt of y increases to the same as x; thermal equilibrium is reached.

Question 11

Convection Answ formula

Answer 11

Liquid/air expands due to heating via conduction -> warmer, less dense, rises to top -> surrounding denser n cooler liquid sinks in place of rising liquid ->convection currents carry warmer air/liquid away from flame and cooler air towards it.

Question 12

Conduction in metals Answ formula

Answer 12

Metals contain delocalised free-moving electrons, transferring energy via collision w other electrons n atoms, to _.

Question 13

Conduction in non-metals Answ formula

Answer 13

When heated, particles of substance near heat source gains heat, is more energetic, vibrate more vigorously about their fixed positions, transfers thermal energy thru collision w neighbouring particles to the other end of substance.

Question 14

Convection in liquids

Answer 14

Liquid near heat source heated -> volume increases -> warm water less dense and rises -> cooler water sinks and gets heated by heat source -> convection current established, allowing energy transfer throughout the substance.

Question 15

Name characteristics of objects that r good emitters and absorbers of radiation.

Answer 15

S. Tempt: high
S. Colour & texture: black, rough surfaces
S. Area: large

Question 16

Name characteristics of good reflectors of radiation

Answer 16

S. Tempt: low
S. Colour & texture: shiny, silver, smooth surface
S. Area: small

Question 17

Metal and rubber r good conductors of heat since they’re both solids. Dya?

Answer 17

No. While heat is being conducted thru vibrations n collisions of molecules in both solids, heat is conducted much faster in metals due to free-moving electrons. Rate of conduction is much faster in metals than in solids -> metals r btr conductors of heat.

Question 18

Metal + wooden rod rolled in paper heated by a flame. Describe wut will happen.

Answer 18

Paper attached to wooden rod will be burnt but not the one attached to metal rod. The wooden rod is a poor conductor and will not be able to conduct heat quickly enuf before the paper is burnt. Conversely, the metal rod can conduct heat away from the paper b4 it is burnt since it is a better conductor of heat.

Question 19

Explain why you can hold your fingers beside candle flame without harm but not directly over flame.

Answer 19

Air surrounding flame heats up, expands and density decreases, rise up and finger above candle is scalded. However, beside the flame, convection current is established, constantly cooling the air surrounding flame, preventing us from scalding.

Question 20

Ice at bottom of beaker containing water. Explain w reasons where tempt will be higher.

Answer 20

Tempt of water will be higher at the top. Heat is being conducted away from water at the bottom of cylinder to ice. Cooler and denser water remains at the bottom, thus no convection occurs. Thus water at top have a higher tempt than bottom.

Question 21

Heat radiation affecting tempt change

Answer 21

Blac surface is a better absorber of radiation, polished surface is a better reflector of heat. Thus, black x absorbs more heat which translates to a higher tempt change.

Question 22

Explain features of solar heating panel that maximise heating of water

Answer 22

Metal tubes r good conductors of heat
Black surface of tubes is good absorber of radiation
Wide arrangement of pipes increase s.a. -> more heat absorbed.

Question 23

Why is it easier to compress a gas than solid

Answer 23

Molecules of gas r further apart and intermolecular forces of attraction r weaker -> more distance for molecules to move closer tgt.

Question 24

Evidence for motion of gas

Answer 24

Brownian motion. Smoke particles in constant and random motion.

Question 25

State why thermal energy is transferred by conduction thru solids

Answer 25

Energy transfer by conduction occurs most effectively thru solids as particles r closely packed tgt in fixed positions.

Question 26

Lower heat capacity vs higher heat capacity graph

Answer 26

Steeper gradient for tempt rise: lower heat capacity

For the same mass, same period of time, Y takes a longer time to decrease in temperature than Z. This indicates that a higher amount of energy needs to be lost by Y compared to Z for the same amount of fall in temperature.