Heat

Question 1

In what direction does heat energy flow

Answer 1

Heat energy always flows from hot to cold

Question 2

State the energy transfer processes (heat)

Answer 2

Conduction
Convection
Infrared radiation
Evaporation
Condensation

Question 3

What are the factors that affect the rate at which heat energy flows

Answer 3

The factors that affect the rate at which heat energy flows:
The temperature difference between the two objects
The surface area of an object
The colour of the object

Question 4

What happens when the temperature of an object increases, in terms of internal energy

Answer 4

When the temperature of an object increases, the energy stored in the object increases (the object’s internal energy increases)

This is because heating causes energy to be transferred to an object’s particles, this increases the kinetic energy store of the particles causing them to move faster. This results in an increase in internal energy, which causes an increase in temperature

Question 5

Complete the sentence
The energy stored in an object is called its ____________

Answer 5

The energy stored in an object is called its internal energy

Question 6

Define internal energy

Answer 6

Internal energy is the total kinetic energy and potential energy of all the particles (atoms and molecules) that make up a system.

Question 7

State the ways in which energy can flow

Answer 7

Energy can flow by:
Conduction
Convection
Infra-red Radiation

Condensation
Evaporation

Question 8

Complete the sentence
The more delocalised electrons, _____________

Answer 8

Complete the sentence
The more delocalised electrons, the higher the rate of conduction

Question 9

What does a high thermal conductivity mean in terms of energy transfer in a metal

Answer 9

The higher the thermal conductivity of a material, the higher the rate of energy transfer by conduction across that material

Question 10

Define conduction

Answer 10

A method of energy transfer by heating where vibrating particles transfer energy through a material by colliding with neighbouring particles and transferring energy between their kinetic energy stores

Question 11

In what type of material does conduction occur in

Answer 11

Conduction occurs in solids

Question 12

What type of materials are the best insulators

Answer 12

Non-metal materials such as wool and fibreglass are the best insulators

Question 13

What type of material is the best conductors

Answer 13

Metals are the best conductors

Question 14

What is a fluid

Answer 14

A fluid is a gas or a liquid

Question 15

Explain the process of conduction through metals

Answer 15

The metal has delocalised electrons
The delocalised electrons gain energy when the metal is heated and move faster through the metal.
The delocalised electrons collide with other electrons transferring kinetic energy to them.
This increases the internal energy of the metal causing an increase in temperature.

Question 16

Explain the process of conduction through non-metals

Answer 16

The heat energy is conducted from the hot end of the object to the cold end of the object
It is transferred from atom to atom.

The atoms in the part of the object being heated vibrate faster and collide with each other more.

The collisions cause energy to be transferred between the atoms’ kinetic energy stores.

This process continues throughout the object until the energy is transferred to the other side of the object.

It is then usually transferred to the thermal energy store of the surroundings (or anything else touching the object)

Energy is transferred by conduction through the metal pan handle
Energy is transferred by conduction through the pan to the water

Question 17

Why are all metals good conductors of heat (and electricity)

Answer 17

Metals have delocalised electrons.
These electrons can travel through the metal, transferring the energy more quickly

Question 18

Why are metals better conductors of heat (and electricity) than non-metals

Answer 18

Metals have delocalised electrons.
These electrons can travel through the metal, transferring the energy more quickly
Non metals do not have delocalised electrons and pass on (transfer) heat energy by the vibrations of atoms. This process is very poor.

Question 19

Define convection

Answer 19

Convection is a method of energy transfer by heating in liquids and gases in which energetic particles move away from hotter regions to cooler regions

Question 20

Describe the process of convection

Answer 20

When the air/liquid is heated, the particles gain energy.

Therefore they move faster and their separation is further, causing a decrease in density.

Less dense and hotter air/liquid will rise above the more dense, colder air/liquid.

The cold, more dense air/liquid takes the place of the hotter, less dense air/liquid and the process continues

Question 21

In what types of material does convection occur

Answer 21

Convection occurs in fluids (anything that can flow) - gas or a liquid

Question 22

What is infra-red radiation

Answer 22

Infra-red radiation is the transfer of heat energy by an electromagnetic wave.

Question 23

In terms of radiation, what do all objects do.

Answer 23

All objects continually emit and absorb infra-red radiation

Question 24

Complete the sentence
Energy is _________ being transferred to and from ___________ (emitted and absorbed), even through empty space (a __________)

Answer 24

Complete the sentence
Energy is continually being transferred to and from objects (emitted and absorbed), even through empty space (a vacuum) - they do both at the same time

Question 25

In terms of radiation, what effect does the hotness of object have

Answer 25

The hotter an object is, the more energy it radiates (the more infra-red radiation it emits in a given time)

Question 26

In terms of radiation, what effect does the colour of object have

Answer 26

Dark matt surfaces emit and absorb more radiation than light shiny surfaces AT THE SAME TEMPERAUTRE

Question 27

Which colours emit and absorb less radiation in comparison to other colours

Answer 27

Light shiny surfaces emit and absorb less radiation than dark, matt surfaces AT THE SAME TEMPERATURE

Question 28

Which colours are good and poor reflectors and absorbers of infra-red radiation

Answer 28

Dark, matt surfaces are good absorbers and emitters (poor reflectors) of radiation
Light, shiny surfaces are good reflectors (poor absorbers and emitters) of infra-red radiation.

Question 29

Why can infra-red radiation travel through a vacuum.

Answer 29

No particles are involved in the transferring of heat energy by infra-red radiation.

Question 30

Metals have ____ thermal conductivity and transfer heat energy rapidly
Non-metals have a _______ thermal conductivity which is why they are used as insulators
Fluids have a _______ thermal conductivity

Answer 30

Metals have high thermal conductivity
Non-metals and fluids have a low thermal conductivity
Fluids have a low thermal conductivity

Question 31

Why does conduction occur mainly in solids and not in liquids/gases

Answer 31

Conduction occurs mainly in solids as the particles in a solid are held together really closely which means there are lots of collisions that pass on the energy whereas in liquids and gases, the particles are all further apart and so they don’t collide as much

Question 32

Why does convection occur mainly in liquids/gases and not in solids

Answer 32

Particles in liquids and gases are much more free to move around which is why they usually transfer energy by convection whereas in solids the particles are next to each other in fixed positions.

Question 33

In terms of infra-red radiation explain how the temperature of an object can increase

Answer 33

The temperature of an object increases if it absorbs more infrared radiation than it emits

Question 34

How does surface area affect the rate at which heat energy flows

Answer 34

The smaller the surface area of an object, the lower the rate at which heat energy is lost from an object by conduction and convection

Question 35

How does the temperature difference between two objects affect the rate at which heat energy flows

Answer 35

The greater the temperature difference is between two objects, the greater the rate at which heat energy is lost from an object by conduction, convection and infra red radiation

Question 36

In terms of infra-red radiation, what does a constant temperature mean

Answer 36

An object at a constant temperature emits infrared radiation at the same rate as it absorbs it

Question 37

In terms of infrared radiation, what does an object that is hotter than it surroundings do.

Answer 37

An object that’s hotter than its surroundings emits more Infrared radiation than it absorbs as it cools down (e.g. a cup of tea left on a table

Question 38

In terms of infrared radiation, what does an object that is cooler than it surroundings do.

Answer 38

An object that is cooler than its surroundings absorbs more infrared radiation than it emits as it warms up (e.g. a cold glass of water on a sunny day.

Question 39

What do hot bodies mainly emit

Answer 39

Hot bodies mainly emit infra-red radiation