Chapter #11 - Thermal Energy Transfers

Question 1

Why does a metal conduct heat faster than a non-metal?

Answer 1

Because the iron has free electrons which can move and carry the heat faster than just the vibrating of the atoms being passed on.

Question 2

What are the three main forms of heat transfer?

Answer 2

• Conduction
• Convection
• Radiation

Question 3

Why does hot air rise?

Answer 3

Because when there is more kinetic energy in particles (hot air) this causes them to move faster. Because of this, the particles are less dense, so the particles rise.

Question 4

Why is the deepest part of a swimming pool colder than the surface?

Answer 4

Because, when water gets warmer it expands, causing the particles to be less dense. If the particles cool, than they move slower and become more dense and sink to the bottom.

Question 5

How well do gases conduct?

Answer 5

They are the worst

Question 6

What object emit infrared radiation?

Answer 6

All objects emit infrared radiation.

Question 7

What objects emit more radiation?

Answer 7

The hotter the object, themore radiation it emits.

Question 8

How do you limit radiation?

Answer 8

By using emiters.

Question 9

What are good emiters?

Answer 9

A shiny or white surface (it reflects the radiation).

Question 10

What are absorbers of infrared radiation?

Answer 10

Black objects

Question 11

What are the charectaristics of radiation?

Answer 11

1. The hotter the object is, the more radiation it gives out.
2. Only form of thermal energy tarnsfer which soes not need a medium to travle througth.
3. Travel through a vacume.
4. Invisible to the naked eye.
5. Can be detected by nerve cells on skin
6. Warms the object that absorbs it.

Question 12

Which way does thermal energy transfer?

Answer 12

From hot places to cold places.

Question 13

How do you keep energy in a place that is hotter?

Answer 13

By insulationg it.

Question 14

How does convestion work with a heater?

Answer 14

Thermal energy will be movng from the around the room from the heater as a result of convestion currents, which rise drom the heater.

Question 15

How does convestion work with a refigerator?

Answer 15

Cold air sinks to the bottom,Cold air remains there and food at top would not be cold.

Question 16

What is thermal comduction?

Answer 16

The transfer of thermal energy by the vibration of particles.

Question 17

What is the defenition of convection?

Answer 17

The transfer of thermal energy through a fluid by the movement of the material itself.

Question 18

What are some methods of home insulation?

Answer 18

• Thick curtains, draught excluders
• Loft and underfloor insulating
• Double and triple glazing of windows
• Cavity walls
• Foam or rockwool in wall cavity

Question 19

Why do thick curtains, draught excluders work for home insulation?

Answer 19

Stops convection currents, and so prevents thermal energy transfer.

Question 20

Why do loft and underfloor insulating materials work for home insulation?

Answer 20

Prevents conduction of thermal energy tgrough floors and ceilings.

Question 21

Why does double and triple glazing windows work for home insulation?

Answer 21

Vacuuum between glass panes cuts out lossses or gains by conduction or convection.

Question 22

Why do cavity walls work for home insulation?

Answer 22

Reduces thermal loss or gain by conduction.

Question 23

Why does foam or rockwool in wall cavity work for home insulation?

Answer 23

Further reduces thermal energy transfer by convection.

Question 24

How much thermal energy is usually lost throught the walls?

Answer 24

33%

Question 25

How much thermal energy is usually lost throught the windows?

Answer 25

18%

Question 26

How much thermal energy is usually lost throught the floors?

Answer 26

8%

Question 27

How much thermal energy is usually lost throught the roof?

Answer 27

26%

Question 28

How much thermal energy is usually lost throught the space under the doors?

Answer 28

12%

Question 29

How much thermal energy is usually lost throught the doors?

Answer 29

3%

Question 30

What is the construction of a vacuum flask?

Answer 30

• Glass used as great insulator
• Vacuum in gap between double walls to reduce losses of conduction and cnvection.
• Silver coating on glass reduces losses by radu«iation by reflecting any infrared radiation.
• Plastic stopper prevents losses by conduction and evaporation.

Question 31

How does the car system use specific heat cpacity to keep the car engine cool?

Answer 31

Water flows around the block to absorb the thermal energy. Water is a good choice as it has a very high specific heat capacity.

Question 32

How does the car system use convection to keep the car engine cool?

Answer 32

As water is heated, a convection current flows. The pumo is used to speed uo this flow.

Question 33

How does the car system use conduction to keep the car engine cool?

Answer 33

The radiator has metal fins so the thermals energy is conducted to all parts of the radiator.

Question 34

How does the car system use radiation to keep the car engine cool?

Answer 34

The fins have a large surface area and are black to increase the rate of thermal energy radiation.