4.1- 4.1.6 Energy stores and transfer

Question 1

Where is thermal energy transferred from

Answer 1

a place that is hotter or a high tempreture to an area with a lower tempreture or cooler

Question 2

What are the 3 processes of energy transfer

Answer 2

Conduction, Convection and radiation

Question 3

What is Conduction

Answer 3

The transfer of thermal energy through a substance by the vibrations of atoms within a substance

Question 4

Explain conduction

Answer 4

The process of conduction happens by the vibrations between the atoms of a substances these vibrations transfer kinetic energy from particles to other particles which is then transferred into thermal energy there will be more energy gained from this

Question 5

What is convection

Answer 5

Convection is the transfer of heat through fluids by the upwards movement of warmer less dense regions of fluid and the downwards movement of more dense cooler particles.

Question 6

Explain Convection

Answer 6

In convection the heated liquid will expand and become less dense then the cooler surrounding water. The warmer liquid rises to the top of the area and the cooler dense liquid sinks and takes its place At the top the warm liquid starts to cool and become more dense. It will begin to sink the cooler water then heats and rises so a circulation current is set in the water this is the convection current.

Question 7

Give an example of convection occurring in everyday phenomena

Answer 7

In many cooking ovens the heating element is placed at the bottom of the oven it heats the air nearest to it, and the air rises due to convection. The top of the oven is generally warmer than the bottom is. Air and water also allow heat transfer to take place by convection as both are fluids and good insulators

Question 8

What is thermal radiation

Answer 8

The transfer of energy by infrared waves

Question 9

What effects how much an object radiates

Answer 9

the hotter the object the more it radiates, the colour Black objects are the best at emitting and absorbing heat shiny object are the worst at emitting and absorbing thermal radiation

Question 10

Explain which colours are the best and worst at absorbing and emitting radiation

Answer 10

-black good absorber good emitter
-dull/dark reasonable absorber/reasonable emitter
-white poor absorber poor emitter
-shiny very poor absorber very poor emitter

Question 11

Explain how the 3 energy transfers occur in a in a hot cup of coffee

Answer 11

-Energy is transferred by heating from the bottom of the mug to the surface its in contact with energy transfer will happen through conduction
-Energy is transferred by radiation to the surrondings
-As heat rises due to convection most of the hot liquid is at the surface of the coffee so stream will rise away from the coffee due to the process of convection

Question 12

Why will the coffee continue to lose heat

Answer 12

Hot liquids will tend to lose heat until they reach a thermal equilibrium

Question 13

Why are metals good conductors

Answer 13

Metals are good conductors as their delocalised electrons can collide with the atoms helping to transfer the vibrations through materials and hence transfer heat better. Delocalised electrons in metals speed up thermal conductions

Question 14

Why are noon-metals poor conductors or insulators

Answer 14

Non-Metals are poor conductors or insulators because they have very few free electrons to transfer vibrations through materials so they cannot transfer heat well. The same with gases and liquids they do not have any free electrons so they cannot pass on the current

Question 15

Explain how emission and absorption of radiation is related to surface area

Answer 15

If surface area is a good reflector of infrared radiation then it is a poor emitter of IR. This means that a hot object with a shiny surface will emit less heat energy in the form of infrared radiation than other object of the same tempreture with a matt black surface. A kettle with a shiny surface is shiny to reduce the rate of heat loss

Question 16

Explain different ways of reducing unwanted energy such as insulation

Answer 16

-Few ways to reduce unwanted energy and improve insulation in houses for example glass is a poor thermal conductor but it is used in thin layers, to improve insulation properties double glazed windows are installed Where there are two layers of glass to trap a layer of air the thickness of the glass is important though because if it is too thin then the insulation effect will be reduced but if it is too thick then the convection currents will be able to circulate and carry heat from the hotter surface to the cooler one

Question 17

Explain another way of reducing unwanted energy loss and improving insulation

Answer 17

Roof insulation in a modern house uses similar panels to those used in wall cavities, it traps thick layers of air. This takes advantage of the poor conducting property of air whilst preventing convection current circulating the molecules in air are not close enough to transfer heat

Question 18

Where is most radiation lost in the house

Answer 18

-Walls 35%
-Roof 25%
-Floor 15%
-Door 15%
-Windows 10%