Thermal Energy Transfer

Question 1

A 125cm beaker and a 250cm beaker are filled with hot water with a thermometer in them. Which one will cool down faster?

Answer 1

The water in the large beaker will lose thermal energy faster because the surface in touch with the air is greater, so thermal energy escapes faster

Question 2

whats the lowest temperature that the water will reach

Answer 2

the room temperature, it wont lose thermal energy anymore

Question 3

Particles of a solid

Answer 3

vibrate around stable positions, very close to each other

Question 4

particles of a liquid

Answer 4

vibrate, close together, but can still move/flow past each other. They diffuse in the entire container

Question 5

particles of gas

Answer 5

diffuse in the entire container. can spread apart from each other

Question 6

when the temperature of a solid, liquid or gas is raised…

Answer 6

its particles move faster in all directions and the thermal energy of the object is increased

Question 7

when the temperature of a solid is increased…

Answer 7

its particles vibrate faster, push each other apart and spread out. As the distance among particles increases the solid expands and becomes less dense

Question 8

why does the solid become less dense when heated?

Answer 8

When heated the solid expands and therefore the volume increases. Density is mass/volume

Question 9

when the temperature of a liquid is increased…

Answer 9

its particles vibrate faster push each other apart and spread out. They also diffuse faster in the entire liquid

Question 10

when the temperature of a gas increases…

Answer 10

the gas particles hit the walls of the container with high speed. If the walls are not rigid, the container expands

Question 11

conduction

Answer 11

• transfer of thermal energy between substances that are in direct contact. Its transferred from a hotter part to a colder part. Particles pass their kinetic energy one to another via collision.

Question 12

Particles are transferred by…

Answer 12

collisions

Question 13

conduction happens best in….

Answer 13

solids

Question 14

Conductors…

Answer 14

transfer thermal energy easily

Question 15

insulators…

Answer 15

transfer thermal energy poorly

Question 16

example of conductor…

Answer 16

steel, copper

Question 17

example of insulator…

Answer 17

wood , plastic

Question 18

why are handles on pans wooden?

Answer 18

wood is an insulator so it prevents your hands from burning

Question 19

why are pans made of steel

Answer 19

it transfers thermal energy from the hob to the food easily

Question 20

convection is

Answer 20

transfer of thermal energy through fluids. It occurs when an area of a liquid or gas rises because their density decreases. Cooler water sinks in and rushes to replace them. This creates a pattern called convection current

Question 21

convection summary…

Answer 21

hot water rises because of its low density, cold water sinks and replaces it. Its transferred by the flow of particles

Question 22

radiation is

Answer 22

the transfer of thermal energy that doesnt require contact between the energy source and the heated object. It can happen through empty space ( no particles required )

Question 23

What colours absorb thermal energy?

Answer 23

dark dull surfaces

Question 24

what colors reflect thermal energy

Answer 24

light, shiny surfaces

Question 25

why are houses in hot countries painted white

Answer 25

so they reflect energy transferred by radiation

Question 26

hot water tanks have a heater in the bottom rather than the top

Answer 26

water in the bottom becomes less dense when heated and therefore rises. Then cold water replaces the hot water and the same pattern continues. If the heater was at the top, then the hot water would never rise and cold water would stay down without being heated.

Question 27

what is a vacuum

Answer 27

an empty space with no particles or air

Question 28

how does thermos stop convection?

Answer 28

the vacuum has no particles to carry thermal energy by convection. The stopper also reduces heat loss by convection

Question 29

how does thermos stop conduction?

Answer 29

the vacuum has no particles to carry thermal energy by conduction. The double glass shell traps air and prevents conduction. The stopper is made up of plastic which is an insulator and prevents conduction from occuring

Question 30

how does thermos stop radiation?

Answer 30

its silver coating reflects radiation

Question 31

how thermal energy is transferred along a glass rod

Answer 31

by conduction. As you heat the glass, the particles vibrate, these vibrations cause other particles to vibrate. As the vibrations are passed along the glass, so is the thermal energy

Question 32

how does a heater that’s in the corner of a room warm the whole room up?

Answer 32

Convection occurs. The air next to the heater warms up. This causes the particles in the air to move faster. The air expands. It becomes less dense than the surrounding air, so it rises. Colder air rushes to replace it. This pattern repeats creating a convection current.