P1.1 ~ Energy Transfer

Question 1

What is infrared radiation?

Answer 1

Thermal (infrared) radiation is the transfer of thermal energy (heat energy) by electromagnetic waves; no particles of matter are involved

Question 2

What do all objects do?

Answer 2

Emit and absorb thermal radiation

Question 3

What happens if an object is hot?

Answer 3

More energy will be radiated

Question 4

What does the amount of thermal radiation given out depend on?

Answer 4

It’s surface, shape and dimensions.

Question 5

What would cause an object to absorb energy faster?

Answer 5

A big difference in temperature between the object and its surroundings.

Question 6

How can the rate of heat transfer be slowed?

Answer 6

By the use of insulation, which provides a barrier.

Question 7

How do different materials (dark matt surfaces and light shiny surfaces) transfer heat at different rates?

Answer 7

At the same temperature:
~ dark matt surfaces emit more radiation than light shiny surfaces
~ dark matt surfaces absorb more radiation than light shiny surfaces because light shiny surfaces are good reflectors of infrared radiation

Question 8

What is the kinetic energy in solids like?

Answer 8

Solid partials have the least amount of energy. They are not able to move but do vibrate around a fixed point.

Question 9

How does heating a solid affect the kinetic energy?

Answer 9

Heating a solid gives the particles enough energy to move around (although they cannot move far apart) and it melts to become a liquid.

Question 10

How can heating a liquid affect the kinetic energy of the particles?

Answer 10

Further heating can give the particles enough energy to move very quickly. They separate from each other and the liquid evaporates to become a gas.

Question 11

What is conduction?

Answer 11

Conduction is the transfer of heat energy without the substance itself moving.

Question 12

What structure is a good conducter?

Answer 12

Metals

Question 13

What happens when a metal becomes hotter?

Answer 13

It’s tightly packed particles gain more kinetic energy and vibrate. The energy is transferred to cooler parts of the metal by delocalised electrons, which move freely through the metal, colliding with particles and other electrons

Question 14

Why can conduction occur in non-metal solids?

Answer 14

Because the particals can pass energy from one to the next by vibration.

Question 15

Why are non-metals poor conductors?

Answer 15

Due to the lack of free electrons.

Question 16

Why are gases poor conductors?

Answer 16

Because the particles are so far apart.

Question 17

What is convection?

Answer 17

Convection is the transfer of heat energy through movement.

Question 18

Where does convection occurs?

Answer 18

In liquids and gases.

Question 19

What can convection create?

Answer 19

Convection currents.

Question 20

What is condensation?

Answer 20

When the particles in a gas have more energy than those in a liquid. When a gas condenses to form a liquid, this energy is released and can make the temperature increase.

Question 21

When can condensation occur?

Answer 21

When a warm gas comes in contact with a cold surface.

Question 22

When does evaporation occur?

Answer 22

A liquid evaporates when it’s particles have gained enough energy to escape the surface of the liquid and become a gas.

Question 23

What are key features of a vacuum flask?

Answer 23

~ They are usually made from plastic which is a poor conducter
~ Shiny silver sides which reflect infrared radiation and stop heat transfer.
~ A vacuum, which contains no particles so neither conduction not convection can take place
~ A screw top, this can prevent evaporation from the surface and convection currents at the top.

Question 24

What is a U-Value?

Answer 24

The U-Value of a material indicates how effective a material is as an insulator because it can show how quickly heat energy can pass through.

Question 25

Is it better to have a lower or higher U-Value? (and why?)

Answer 25

A low U-Value.
Because that it means that heat flows through it slowly. Therefore the lower the U-Value, the better the material is at insulating.

Question 26

What is the equation to find the payback time?

Answer 26

Total cost of improvement
Payback ————————–
Time = Savings per year

Question 27

What is the specific heat capacity of a substance?

Answer 27

The amount of energy needed to change the temperature of one kilogram of it by one degree Celsius.

Question 28

What happens if something (e.g water) has a high specific heat capacity?

Answer 28

It can store a lot of heat energy without getting too warm. This makes it useful as a coolant.

Question 29

How is heat transferred from homes into the environment?

Answer 29

Conduction ~ though the walls, floor, roof and windows
Convection ~ convection currents coupled with cold drafts from gaps in doors and windows cause heat energy carried by warm air to rise up to the roof space where it is easily lost
Radiation ~ from the surface of the walls, roof and through the windows.

Question 30

Where is heat lost?

Answer 30

Roof ~ 25%
Under doors and windows ~ 15%
Walls ~ 35%
Windows ~ 10%
Floor ~ 15%

Question 31

How can you prevent heat being lost through the roof?

Answer 31

Roof insulation ~ traps a layer of air between fibres or insulating material.

Question 32

How can you prevent heat from being lost through under doors and windows?

Answer 32

Draught excluders ~ keep as much warm air inside as possible.

Question 33

How can you prevent heat loss through walls?

Answer 33

Cavity wall insulation and internal thermal boards.

Question 34

How can you prevent heat loss through windows?

Answer 34

Double glazing ~ traps air between two sheets of glass.

Curtains ~ stop heat loss through convection.

Question 35

How can you prevent heat loss through the floor?

Answer 35

Carpets, rugs and underfloor insulation can stop heat loss through the floor.

Question 36

Advantages and disadvantages of roof insulation?

Answer 36

Advantages
~ can reduce heat loss by 20%
~ many different methods to suit all homes
~ short payback time
Disadvantages
~ requires suitable safety precautions to be taken, e.g. Wearing dust mask

Question 37

Advantages and disadvantages of draught excluders?

Answer 37

Advantages 
~ can reduce heat loss by upto 15%
~ cheap and easy to install
~ short payback time
Disadvantages
~ must make sure that air vents are not blocked - fresh air needs to circulate to prevent dry rot.

Question 38

Advantages and disadvantages of cavity wall insulation?

Answer 38

Advantages
~ can reduce heat loss by 35%
Disadvantages
~ expensive 
~ long payback time

Question 39

Advantages and disadvantages of double glazing?

Answer 39

Advantages
~double glazing traps are between two sheets of glass
Disadvantages
~double glazing can reduce heat loss by up to 10%

Question 40

Advantages and disadvantages of curtains?

Answer 40

Advantages
~Curtains are cheap and easy to install
Disadvantages
~There are none

Question 41

Advantages and disadvantages of carpets?

Answer 41

Advantages
~carpets and rugs are easy to install
Disadvantages
~underfloor insulation is expensive and has a long insulation time