Energy Transfer by Heating

Question 1

How can we detect infrared raditation?

Answer 1

With our skin - it makes us feel warm

Question 2

What do all objects do?

Answer 2

Emit radiation

Question 3

The hotter an object is…

Answer 3

…the more infrared radiation it emits in a given time

Question 4

What is a vacuum?

Answer 4

A region that doesn’t contain any particles.

Conduction and convection cannot occur here, but radiation can

Question 5

What does the transfer of energy by infrared radiation not involve?

Answer 5

Particles

Question 6

What type of surfaces are good absorbers of radiation?

Answer 6

Dark-coloured, matt surfaces

Question 7

If an object is a good absorber of radiation, we also know that it will be a good…

Answer 7

..emitter too. Physics works both ways!

The same is true of reflectors, they are also poor absorbers

Question 8

What type of material is a good reflector and poor absorber of radiation?

Answer 8

Light-coloured, shiny surfaces

Question 9

What are the properties of solid particles?

Answer 9

• Low transactional energy, but still vibrate (vibrational energy)
• Fixed positions due to strong intermolecular bonds
• Fixed + rigid shape
• Not compressable

Question 10

What are the properties of liquid particles?

Answer 10

• Lower energy than gas, higher than solid
• Particles still in contact with each other due to fairly strong intermolecular bonds
• Can move around slightly and form random arrangements
• Therefore, can flow and fit shape of container
• Does not have a fixed shape

Question 11

What are the properties of gas particles?

Answer 11

• High energy (high transactional)
• No fixed positions due to very weak intermolecular bonds
• Therefore they can move randomly and much faster
• No fixed shape and can flow
• Compressable
• Much less dense than solids + liquids

Question 12

Draw a diagram showing the different states of matter

Answer 12

Question 13

When does conduction occur?

Answer 13

In solids (and poorly in liquids)

Question 14

What types of material are the best conductors and why?

Answer 14

• Metals are the best conductors.
• This is because they contain free electrons.
• When heated, these gain energy and move through the metal, transfering energy by colliding with other particles.

Question 15

Describe how conduction works.

Answer 15

• When one end of a solid is heated, the particles at that end gain kinetic energy and vibrate more
• These vibrations pass energy onto neighbouring particles
• This process continues through the solid, passing on slightly less energy each time as some is maintained by each vibrating particle
• This is how energy is transfered through a solid (conduction)

Question 16

What are insulators?

Answer 16

A poor conductor

Question 17

What is a conductor?

Answer 17

A material/substance that conducts energy (via conduction) well…

Question 18

Why are materials such as wool and fibreglass good insulators?

Answer 18

Because they contain trapped air.

Air is a poor conductor because it is a gas, so the particles are much less densely packed and therefore do not transfer energy by conduction very well at all.

Question 19

Where does convection occur?

Answer 19

In fluids

Question 20

What are fluids?

Answer 20

Liquids and gasses

(They can flow)

Question 21

Describe how convection works.

Answer 21

• When a fluid is heated it expands and gains kinetic energy
• The fluid becomes less dense and rises
• As the fluid rises, it begins to loose some of its energy
• This causes it to sink again and become more dense
• It is then heated again and the process continues.
• This forms a convection current

Question 22

What are convection currents responsible for in the real world?

Answer 22

Onshore and offshore breezes

Question 23

Why does a fluid become less dense when it is heated?

Answer 23

Because the particles gain more kinetic energy and move apart.

This causes it to expand.

This means there is the same amount of mass in a larger area.

Question 24

Why does evaportation take place?

Answer 24

Because the most energetic liquid molecules escape the liquid’s surface and enter the air/become a gas

Question 25

How does evaporation also cause cooling?

Answer 25

* Evaportation takes place due to the **most energetic liquid particles escaping the liquid's surface and entering the air**/becoming a gas. * This means that the **average kinetic energy of the remaining molecules decreases**, so the temperature of the liquid also decreases

Question 26

How can the rate of evaportation be increased?

Answer 26

* Increasing the **surface area** * Increasing the **temperature** * Creating a **draught** of air across the liquid's surface

Question 27

How can the rate of condensation be increased?

Answer 27

* Increasing the **surface area** * Decreasing the **temperature**

Question 28

The greater the temperature difference between an object and its surroundings...

Answer 28

...the greater the rate at which energy is transfered

Question 29

What does the rate at which energy is transfered depend upon?

Answer 29

* The **substances/materials the object is in contact with** * The object's **shape** * The object's **surface area** * The **temperature difference** between the object and its surroundings

Question 30

Why might we want to maximise the rate of energy tranfer?

Answer 30

To keep an object cool

Question 31

How can the rate of energy transfer be maximised?

Answer 31

* Use **good conductors** * Use **good emitters** (dark, matt) * **Maximise air flow**/draught

Question 32

How can the rate of energy transfer be minimised?

Answer 32

* Use **good insulators** * Use **good reflectors** (white, shiny) * **Prevent convection currents** by trapping air in small pockets (this also prevents conduction)

Question 33

Draw an label a diagram of a vacuum flask showing how it is a good insulator

Answer 33

* Plastic cap prevents conduction + convection * Double-walled glass/plastic container prevents conduction + radiation00 * Plastic protective cover prevents conduction * Hot/cold liquid * Sponge pad for protection also prevents conduction * Inside surfaces silvered to stop radiation * Vacuum prevents conduction + convection * Plastic spring for support

Question 34

What does a vacuum flask do and why?

Answer 34

Reduces the rate of energy transfer to keep hot things hot and cool things cool

Question 35

What is the specific heat capacity of a substance?

Answer 35

The amount of energy (Joules) required to raise 1Kg of it by 1°C (or K)

Question 36

What does the rate of temperature change in a substance when heated depend upon?

Answer 36

* The amount of energy transfered to it * Its mass * Its specific heat capactity

Question 37

What are U-values and what do they tell us?

Answer 37

The amount of energy per second that passes through a material. The lower the U-value, the better insulator the material is

Question 38

Why do most people want to minimise the rate of energy transfer out of their homes?

Answer 38

To reduce fuel/energy consumption, and therefore fuel/energy bills

Question 39

How can heat transfer out of homes be reduced?

Answer 39

* **Fibreglass loft insulation** to reduce **conduction** * **Cavity wall insulation** **traps air** in small pockets to reduce **covection** + **conduction** * **Double glazing** reduces **conduction** * **Draught proofing** reduces **convection** * **Aluminium foil behind radiators** **reflects infrared raditation** back into the room and therefore reduces **radiation** * **Thick curtains** reduce **conduction and radiation**

Question 40

How do solar heating pannels work?

Answer 40

* They **contain water that is heated by infrared radiation from the Sun**. * This water may then be used to **heat buildings** or **provide domestic hot water**. * The **pipes** that contain the water are often **painted black** because it both a **good absorber and emitter of radiation**.

Question 41

What are the benefits and drawbacks of solar heating panels?

Answer 41

* They are cheap to run because they do not use fuel * They do not contribute to global warming because they do not produce greenhouse gasses when heating water However: * They are expensive to buy + install * They do not heat water at night