Heat Transfers

Question 1

Density

Answer 1

A substance’s mass per unit of volume or how dense/compact an object is, measured in kg/m3 or g/cm3

Question 2

How do you calculate density?

Answer 2

Density = mass ÷ volume

Question 3

Mass

Answer 3

The amount of matter an object is made of, measured in g or kg

Question 4

Volume

Answer 4

The amount of space an object takes up, measured in m3 or cm3

Question 5

Do objects made of the same material have the same density despite the mass?

Answer 5

Yes

Question 6

Do objects that are less dense float on those that are more dense, despite the mass of the object?

Answer 6

Yes

Question 7

What is the average density of water?

Answer 7

1000kg/m3 or 1g/cm3

Question 8

What is the most dense state of matter?

Answer 8

Solid

Question 9

What is the least dense state of matter?

Answer 9

Gas

Question 10

How are particles in a solid arranged?

Answer 10

Close together vibrating in fixed positions

Question 11

How are particles arranged in liquids?

Answer 11

Close together,moving at random velocities

Question 12

How are particles arranged in gases?

Answer 12

Far away from each other moving at random velocities

Question 13

Heat always flows DOWN a temperature gradient, meaning that….

Answer 13

Heat flows from a hotter part of an object to a cooler part

Question 14

What temperature is absolute zero?

Answer 14

0°K or -237°c

Question 15

What happens when an object reaches absolute zero?

Answer 15

The particles stop moving completely, as they are out of energy

Question 16

Conduction

Answer 16

When a substance is heated, its particles gain MORE energy and vibrate MORE vigorously, and particles bump into those nearby and send thermal vibrations through the substance. This sends thermal energy through the object from the heated side to the cooler, unheated side. Conduction can only occur in solids as the particles must be vibrating in fixed positions to transfer energy throughout the substance.

Question 17

What are materials that are good at conduction called?

Answer 17

Conductors

Question 18

What are objects that are bad at conducting heat called?

Answer 18

Insulators

Question 19

Why are metals better than non-metals at conducting heat?

Answer 19

In non-metals heat can only be transferred slowly via vibrations from particles that are next to each other, whereas in metals, atoms have free electrons that can move around the solid and transfer vibrations quicker and more easily, making metals better than non-metals at conduction.

Question 20

why can’t conduction occur in fluids (gasses or liquids)?

Answer 20

For conduction to occur, particles must be in fixed positions, but in fluids this is not the case, as they are freely moving around at random velocities.

Question 21

convection

Answer 21

when fluids are heated, the particles move faster and then spread out more. This causes them to become less dense and float up, as less dense things float over denser ones.

Question 22

convection current

Answer 22

particles gain more energy from being heated so move faster and spread out, becoming less dense and then rise up. As the particles cool, they lose energy and move slower and move closer together, becoming more dense. This causes them to sink to the bottom, where they will get more heated and start gaining energy, getting faster and starting the whole process over again.

Question 23

Infared radiation

Answer 23

The electromagnetic wave emitted from hot objects. The hotter the object, the radiation it emmits

Question 24

Radiation

Answer 24

The emission of heat as electromagnetic (usually) infrared waves from hot objects

Question 25

Energy is always conserved so ………

Answer 25

The total energy reflected and absorbed is always **equal**.

Question 26

Are black objects poor absorbers or reflectors of radiation?

Answer 26

Poor reflectors

Question 27

Are white objects poor absorbers or reflectors of radiation?

Answer 27

Poor absorbers

Question 28

Why are black objects good at emitting heat?

Answer 28

As darker objects absorb radiation, they become heated quickly. This cause them to emit lots of radiation, as hotter objects emit more radiation, preventing them from retaining any radiation.

Question 29

Why are white objects bad at emitting heat?

Answer 29

As whiter objects reflect more radiation, not much is absorbed. Because not much is absorbed, the object doesn’t heat up so therefore doesn’t intensely emit radiation, and retains it.

Question 30

Evaporation

Answer 30

- particles in liquids have varied kinetic energy - faster particles are able to escape liquid bc they have higher kinetic energy = warmer + lighter so can rise - when faster particles leave, average kinetic energy drops = liquid cools - thermal energy of surroundings is absorbed, so liquid warms slightly and starts cycle again

Question 31

What factors increase evaporation?

Answer 31

- increased temperature - increased surface area - lack of humility - increased wind speed

Question 32

How can a hydro flask prevent heat loss?

Answer 32

- plastic lid: plastic is insulator = prevents heat loss via conduction + lid prevents heat loss via evaporation = fastest particles can’t leave liquid and cool it. - vacuum + trapped air space: prevents convection = air is trapped and can’t rise out of air space + prevents conduction = air is an insulator & conduction can’t occur in a gas - silver: prevents radiation = silver surfaces are poor emmiters of radiation - raised base: prevents conduction as conduction can’t occur through air