transfer of thermal energy and its effect (from notes)

Question 1

thermal energy

Answer 1

energy possessed by a system due to temp

Question 2

Rule for transfer of TE

Answer 2

TE is transferred from a region of higher temp to lower temp until both regions have the same temp

Question 3

blocks in contact

Answer 3

TE transferes from the hotter obj to the cooler obj. hotter obj loses TE while cooler obj gains TE. temp of hoter obj drops and temp of cooler obj rises.

Question 4

blocks in contact after some time

Answer 4

when both objects are sat ht esame temp, there is no NET transfer ofthermal energy between objects. NO MORE GRADIENT

Question 5

SI unit for thermal energy

Answer 5

Kelvin (K) (capital K)

Question 6

temperature

Answer 6

measure of AVERAGE KE of particles in system.

Question 7

SI unit for temperature

Answer 7

K

Question 8

relationship between degrees C and K

Answer 8

0K = -273degreesC

Question 9

which state of matter expands and contracts the most

Answer 9

gas

Question 10

are size of particles changed by heating/cooling of object

Answer 10

NO

Question 11

what changes when object heats/cools (particulate)

Answer 11

spaces between particles

Question 12

What happens when water is cooled TO 4 degrees C

Answer 12

contracrs like other liquids

Question 13

What happens when water is cooled to BELOW 4 degrees C

Answer 13

expands

Question 14

when is the density of water greatest

Answer 14

4 degrees C

Question 15

Is ice or water denser

Answer 15

water

Question 16

bimetallic strip

Answer 16

made up of 2 metals that expand at different rates upon the same temperature

Question 17

metals suitable for bimetallic strip

Answer 17

brass (expands and contracts more)
Steel (expands and contracts less)

Question 18

Where are bimetallic strips used

Answer 18

bimetallic thermometers
thermostats

Question 19

How does a bimetallic strip work in a thermostat (scenario: oven)

Answer 19

When the heater in the oven is switched on, the bimetallic strip expands.
brass expands more than steel, causing the bimetlalic strip to bend away from contact.
This results in an open circuit.
heater stops heating, and the oven starts to cool down.
bimetallic strip cools down and returns to its original position.
circuit closes, and the heater starts to work again.
cycle repeats to maintain a constant temperature in the oven.

Question 20

three main ways to transfer thermal energy

Answer 20

conduction
convection
radiation

Question 21

what is necessary for conduction to occur

Answer 21

physical contact

Question 22

conduction definition

Answer 22

transfer of thermal energy through a medium without the physical movement of the medium itself

Question 23

what level does conduction happen at

Answer 23

atomic level

Question 24

how does conduction occur

Answer 24

one part of obj heated, particles at heated area gain thermal energy and vibrate/move vigorously

these particles collide with neighbouring particles to transfer energy and make them vibrate/move faster and more vigorously

process continues until energy is passed down to cooler end of obj and all particles vibrate/move faster and more vigorously

Question 25

which state of matter conducts thermal energy best

Answer 25

solids

Question 26

which state of matter conducts thermal energy slowest

Answer 26

gas

Question 27

why are solids the best thermal conductors out of the 3 states of matter

Answer 27

their particles are most closely packed together, and are regularly arranged in fixed positions so it is easier to transfer energy

Question 28

why are metals better thermal conductors than most non-metals

Answer 28

metals have free electrons to help transfer energy quickly

Question 29

if water in a test tube is heated on one end and the other side contains ice, will the ice cubes melt

Answer 29

no/after very long. water is a very poor thermal conductor. rate of thermal energy transfer will be very slow

Question 30

convection definition

Answer 30

transfer of thermal energy due to movement of medium, arising from density differences in the medium

Question 31

what is the main form of heat transfer in liquids and gases? why?

Answer 31

convection. particles of liquids and gases are free to move about

Question 32

does convection occur in solids? why?

Answer 32

no. atoms in solids only vibrate about their fixed positions

Question 33

how does convection work in heating

Answer 33

liquid/gas is heated at the bottom. EXPANDS to become LESS DENSE and RISES to the top. COOLER liquid/gas at the TOP is DENSER so it SINKS down to be heated. process continues to set up a CONVECTION CURRENT to heat up all the liquid/gas

Question 34

how does convection work in cooling

Answer 34

liquid/gas is cooled at the top. CONTRACTS to become DENSER and SINKS to bottom WARMER liquid/gas at the bottom is less dense so it RISES up to be cooled. process continues to set up a CONVECTION CURRENT to cool down all the liquid/gas

Question 35

how should you draw convection current

Answer 35

1. curved lines 2. cover entire inline(??) of container

Question 36

convection in nature

Answer 36

sea breeze (daytime) land breeze (night-time)

Question 37

radiation definition

Answer 37

transfer of thermal energy in the form of infrared radiation without the need of a medium

Question 38

when will an object emit thermal energy by radiation

Answer 38

when an obj is warmer than its surroundings

Question 39

when will an obj absor thermal energy by radiation

Answer 39

when the obj is cooler than its surroundings

Question 40

factors affecting rate of radiation

Answer 40

nature of surface surface area of obj surface temperature of obj

Question 41

nature of surface affecting rate of radiation

Answer 41

texture: rougher surface, faster radiation is absorbed or emitted colour: darker surface, faster radiation is absorbed or emitted

Question 42

surface area of obj affecting rate of radiation

Answer 42

larger surface area, higher rate of radiation absorbed/emitted

Question 43

surface temp of obj affecting rate of radiation

Answer 43

higher surface temp, higher rate of radiation emitted