physics chapter 10

Question 1

what is thermal energy

Answer 1

always flows from a region of higher temperature to a region of lower temperature

Question 2

what is the difference in temperature

Answer 2

net flow of thermal energy

Question 3

what is conduction

Answer 3

transfer of thermal energy through solids

Question 4

what is the thermal conductivity of a material

Answer 4

depends on how quickly thermal energy is transferred from the hotter end to the colder end

Question 5

what do the good thermal conductors do

Answer 5

transfer thermal energy quickly

Question 6

what do bad thermal conduction do

Answer 6

transfer thermal energy slowly

Question 7

what is a bad thermal conductor also called

Answer 7

insulator

Question 8

state some of the materials in order that are considered as the best conductors to the worst conductors of thermal energy

Answer 8

diamond, copper, steel, ice, polythene, fibreglass, polystyrene and air

Question 9

state some of the materials in order that are considered as the best insulators to the worst insulators of thermal energy

Answer 9

air, polystyrene, fibreglass, polythene, ice, steel, copper and diamond

Question 10

how can we investigate the transfer of thermal energy through solids

Answer 10

1. for the drawing of the pins to fall, the wax on the four rods must melt. the wax is melted because thermal energy was transferred from the ends of the rods heated by the bunsen burner to the ends of the rods at room temperature. the transfer of thermal energy through the rods occurred without any flow of the material the rods were made of. this means that the thermal energy was transferred by conduction
2. the time taken for the drawing of the pins to fall for each of the four rods was different. this shows that different materials conduct thermal energy at different rates. the time taken is the shortest copper is the best and glass is the worst thermal conductor among the four materials

Question 11

how does conduction work in metals

Answer 11

through lattice vibrations of particles and movement of free electrons

Question 11

how does conduction work in non metals

Answer 11

only lattice vibrations of particles take place

Question 11

why are liquids and gases bad thermal conductors

Answer 11

particles in liquids and gases are spaced further apart than those in solids. collisions between the particles in liquids and gases are less frequent. transfer of kinetic energy from the fast moving particles to neighbouring particles is slower. therefore, air and water are bad thermal conductors

Question 12

what is convection

Answer 12

transfer of thermal energy in a fluid by means of convection currents due to a difference in density

Question 12

describe convection

Answer 12

• convection currents only occur in fluids not in solids
• this is because convection involves the bulk movement of the fluid that carries the thermal energy. this means that for convection currents to occur in a substance, the substance must be able to flow
• in solids, the particle are held in fixed positions, hence the solid cannot flow. they can only transfer thermal energy from one particles to another through lattice vibrations

Question 13

how do liquids and gases transfer thermal energy

Answer 13

1. the incense stick is used to produce smoke that trace the convection currents.
2. the candle below the chimney on the right is lit. the incense stick is held over the left chimney. the smoke is drawn down across the right chimney and rises up above the candle. this shows the circulating convection currents in the air

Question 14

why do convection currents form

Answer 14

convection currents form because of the difference in density in air when heated.

Question 14

what is conduction

Answer 14

still occurs in liquids, but is much slower compared to convection

Question 15

what is thermal radiation

Answer 15

transfer of thermal energy in the form of invisible waves which can travel through a vacuum.

Question 15

what is thermal radiation

Answer 15

it is also known as infrared radiation. all objects absorb and emit infrared radiation. invisible radiation that carries thermal energy

Question 16

how can we investigate the emission of difference surfaces

Answer 16

dull and black surfaces emit infrared radiation at a faster rate than shiny and silver surfaces

Question 17

how can we investigate the absorption of different surfaces

Answer 17

dull black surfaces absorb infrared radiation at a faster rate than shiny silver surfaces

Question 17

what factors affect the emission and absorption of thermal radiation

Answer 17

• high surface temperature
• larger surface area

Question 18

what factors affection the emits the absoprtion affect the temperature of an object

Answer 18

• infrared radiation abosrbs, the object warms up
• infrared radiation absorbed, the radiation in objects cool down

Question 19

what are the consequence of thermal energy during radiation

Answer 19

snow melts at an increases rate, reduced amount of radiation is reflected

Question 19

what are the consequence of thermal energy during convection

Answer 19

- sea breeze and land breeze

Question 19

how does the emission and absorption affect the temperature of an object

Answer 19

the greenhouse effect: natural processes that warms up the earth's surface through a balance of absorption and emissions of infrared radiation

Question 19

what are the application of thermal energy of a good thermal conductor

Answer 19

- cooking utensils - soldering irons

Question 19

what are the application of thermal energy during convection

Answer 19

electrical kettles, air conditioners

Question 20

what are the application of thermal energy of a bad thermal conductor

Answer 20

- handles of cooking utensils - double glazed window

Question 21

what are the application of thermal energy during radiation

Answer 21

green houses