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10DS4 Physics > Heat transfer > Flashcards

Heat transfer Flashcards

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1
Q

What are some different factors that effect the rate of heat transfer?

A

The size of the surface area.
Fins.
The type of material.
If the materials in contact with it are insulators and conductors.

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2
Q

Are metals good conductors of heat?

A

Yes

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3
Q

What are bad conductors of heat called?

A

Insulators

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4
Q

Gas particles:

A 
Almost no forces
Particles have more energy
Free to move
Random directions 
High speed
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5
Q

Liquid particles:

A 
Weaker forces
Particles  are  close together
Can move past each other
Have more energy than solids 
Move at low speeds
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6
Q

Solid particles:

A

Strong forces
Particles are close together
Fixed pattern
Can only vibrate about their fixed position

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7
Q

What do fins in and engine do?

A

Increase surface area to speed up cooling.

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8
Q

If two objects at the same temperature have the same surface area but different volumes, which one will cool more quickly?

A

The one with the smaller volume.

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9
Q

Give an example of how an animal controls heat transfer.

A

Arctic foxes: small ears
small surface area to minimise heat loss
by radiation.
Desert foxes: huge ears
large surface area to allow them to loose
heat loss by radiation.

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10
Q

Describe how a vacuum limits heat transfer.

A

The glass bottle is double-walled with a vacuum between the two walls to stop conduction and convection through the sides.

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11
Q

Heat energy is transferred from the heater coils to the what?

A

Water (conduction)

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12
Q

The particles near the coils get ___________ so they start moving around faster

A

More energy

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13
Q

Heating a room with a radiator relies on?

A

Convection currents

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14
Q

Hot, less dense air by the radiator what flows to replace it?

A

Denser, cooler air

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15
Q

Convection simply cant happen in solids because ….

A

particles cant move

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16
Q

What happens when Gas cools?

A

The particles in the gas slow down and lose kinetic energy

17
Q

How does water vapour condense?

A

It condenses in the air when it comes into contact with cold surfaces

18
Q

Why does invisible water vapour condense?

A

It condenses to form tiny water droplets as it spreads into cooler air

19
Q

What is Condensation?

A

When a Gas turns to a Liquid

20
Q

What is Evaporation?

A

When a Liquid turns to a Gas

21
Q

What is melting?

A

When a solid turns to a liquid

22
Q

What is freezing?

A

When a liquid turns to a solid

23
Q

What is sublimation?

A

When a solid turns straight away to a gas (the liquid part is skipped out)

24
Q

In order for a solid to turn into a liquid and a liquid to turn into a gas what needs to happen to the particles?

A

The particles need to gain more kinetic energy (in order to break bonds)

25
Q

What state of matter has the most kinetic energy within its particles?

A

A Gas

26
Q

What state of matter has the least kinetic energy within its particles?

A

A Solid

27
Q

Explain the process of conduction

A

~ In conduction, one particle gets heated up and passes on its kinetic energy to it’s neighbouring particle (and so on…)

28
Q

Why do metals make good conductors?

A

The metal contains free ions (electrons) which whizz around quickly and pass on the kinetic energy to random particles

29
Q

What do draught excluders do?

A

They are placed at the bottom of doors to minimise cold draughts by CONVECTION CURRENTS

30
Q

What does Double Glazing do?

A

It is an extra layer of glass placed in a window to minimise heat loss by CONDUCTION

31
Q

What do cavity walls do?

A

They are an additional layer of brick placed in walls to reduce heat loss by CONDUCTION

32
Q

What is Cavity Wall Insulation?

A

Foam placed in between cavity walls to reduce heat loss by CONVECTION

33
Q

What do radiator reflectors do?

A

They are a piece of shiny foil placed behind radiators to reflect the heat back into the home

34
Q

What is loft insulation?

A

A thick layer of fibreglass wood laid out across the floor and ceiling of the loft which reduces heat loss by CONDUCTION AND CONVECTION

35
Q

What do thick curtains do?

A

They are big bits of cloth over the window which reduces heat loss by CONDUCTION AND RADIATION

36
Q

What is the formula for Payback Time?

A

Payback time = initial cost/annual saving

37
Q

If the initial cost for installing loft insulation was £200 and the annual saving was £50. What would be the payback time?

A

200/50 = 4 years

38
Q

What is payback time measured in?

A

Years (sometimes can be months e.g. 15/30 can equal to 6 months)

39
Q

The better the insulator the (…….) the U-Value?

A

Lower

10DS4 Physics (4 decks)

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