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Flashcards in Physics 1a Deck (55)
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0

What are the three ways heat is transferred ?

Conduction, convection and radiation

1

How does heat radiation occur ?

Transfer of energy through IR waves

2

Does an object hotter than its surroundings emit more or less radiation ?

More

3

What is the best surface to absorb thermal radiation ?

Dark, Matt surfaces

4

What do light, shiny surfaces do with radiation ?

Reflect it

5

What is conduction ?

The process where vibrating particles pass on their extra kinetic energy to neighbouring particles

6

How do solar panels make the most of thermal radiation ?

The panels are painted black or the pipes painted black. This is to heat water inside them as black absorbs heat.

7

What state does conduction take place in ?

Solids

8

Give an example of a good conductor material ?

Metal

9

Why are metals good conductors ?

Metals have electrons that are free to move. When heated up they bounce off each other transferring energy to the cooler side

10

Where does convection occur ?

Liquids and gases

11

If there is water below the heat source, what does it do ?

Stays cool as relatively no convection occurs

12

How does convection work ?

Water/gas I heated so the particles spread out. Therefore that section of the fluid becomes less dense and rises. As it rises it begins to cool as the heat source is at the bottom. The particles move closer together and then they sink back down as that section of fluid is now more dense.

13

What are some characteristics of a solid ?

Strong forces of attraction hold them in a fixed arrangement / low energy so can only vibrate

14

What state has the most energy ? How can we see this ?

Gas which means they can freely move around us

15

True or false - liquids have weak forces of attraction

True

16

Describe condensation

When a gas turns to a liquid

17

What is evaporation ?

When liquid turns to gas

18

Why does a gas condense ?

When a gas cools net particles slow down and lose energy. The particles are pulled together and become a liquid.

19

What two things allow a liquid particle to evaporate ?

1. If they are traveling in the right direction to escape
2. If they are traveling fast enough

20

How does evaporation occur ?

Particles with the most energy escape because gases have more energy than liquids. When the particles with the most energy have evaporated what is left behind is a liquid with a lower average energy per particle - this means the liquid will have a lower temperature. This is why evaporation can have a cooling effect (think of alcohol hand sanitizing gel).

21

The rate of evaporation will be fast if ......

Temperature is higher / density is lower / larger surface area / higher airflow

22

The rate of condensation is quicker if ........

Temperature of gas is lower / lower the surface the gas touches / higher density / airflow is less

23

What is the formula for payback time ?

Initial cost
---------------------
Annual saving

24

How do vacuum flasks work ?

A vacuum (absence of particles) is contained inside the two walls, this stops convection and conduction. The walls are silvered to reflect IR radiation back into the liquid. The lid is made of foam to stop heat conduction

25

What is cost effectiveness ?

Rather than just looking at how well the energy saving techniques work, it evaluates how much it costs and payback time

26

What does cavity wall insulation prevent ?

Reduces radiation and convection

27

Loft insulation prevents what ? How does it do this ?

Conduction because the fibre glass wool has air gaps which would need convection

28

How do curtains prevent heat loss ?

They form air gaps between the room and glass so it reduces conduction

29

True or False - the lower the
U-Value the better the insulator

True