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GCSE - Physics > Section 3 - Heating Processes > Flashcards

Section 3 - Heating Processes Flashcards

1
Q

Describe solids in terms of particles.

A
  • Strong forces of attraction
  • Particles close together
  • Fixed, regular arrangement -> Particles vibrate on the spot
  • Particles have little energy
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2
Q

Describe liquids in terms of particles.

A
  • Medium forces of attraction
  • Particles close together
  • Particles can move past each other -> Random directions at low speeds
  • Particles have some energy
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3
Q

Describe gases in terms of particles.

A
  • Weak forces of attraction
  • Particles far apart
  • Particles move freely -> Random directions at high speeds
  • Particles have much energy
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4
Q

What happens when you heat a substance?

A

The kinetic energy of the particles increases, so they move faster. This eventually causes solids to melt and liquids to boil.

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5
Q

What must be done in order for a substance to melt or boil?

A

The particles must gain enough kinetic energy to escape the bonds holding them together.

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6
Q

Why are there flat parts on the heating graph of a substance when it is being heated?

A

When a substance is melting or boiling, all of the energy being input is used to break bonds, so the temperature does not rise.

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7
Q

Why are there flat parts on the heating graph of a substance when it is being cooled?

A

When a substance is condensing or freezing, bonds are formed, which releases energy, so the temperature does not go down.

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8
Q

What is specific heat capacity?

A

The amount of energy required to raise the temperature of 1 kg of a substance by 1*C.

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9
Q

What is the specific heat capacity of water?

A

4200J/kg*C

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10
Q

What is the unit for specific heat capacity?

A

J/kg*C

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11
Q

What is the equation for specific heat capacity?

A

Energy transferred (J) = Mass (kg) x S.H.C. (J/kgC) x Temp. Change (C)

E = m x c x 0

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12
Q

What is specific latent heat?

A

The amount of energy needed to change 1kg of a substance from one state to another (without changing its temperature).

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13
Q

Is specific latent heat the same for boiling and melting?

A

No

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14
Q

What is the specific latent heat of vaporisation?

A

The amount of energy needed to change 1kg of a substance from liquid to gas (without changing its temperature).

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15
Q

What is the equation for the specific latent heat of vaporisation?

A

Energy (J) = Mass (kg) x S.L.H. of Vaporisation (J/kg)

E = m x Lv

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16
Q

What is the specific latent heat of fusion?

A

The amount of energy needed to change 1kg of a substance from solid to liquid (without changing its temperature).

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17
Q

What is the equation for the specific latent heat of fusion?

A

Energy (J) = Mass (kg) x S.L.H. of Fusion (J/kg)

E = m x LF

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18
Q

What is the unit for specific latent heat?

A

J/kg

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19
Q

Which way does heat energy tend to flow from and to?

A

From hotter objects to cooler surroundings

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20
Q

What are the three methods of heat transfer?

A
  • Radiation
  • Conduction
  • Convection
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21
Q

What is the main form of heat transfer in solids?

A

Conduction

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22
Q

What is the main form of heat transfer in liquids and gases?

A

Convection

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23
Q

How does temperature difference between a body and its surroundings affect the rate of energy transfer?

A

The greater the difference, the faster heat energy is transferred.

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24
Q

What is heat radiation?

A

The emission of infrared radiation by all objects.

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25
Q

What happens in terms of energy transfer when an object is cooler than its surroundings?

A

It absorbs more infrared radiation than it emits (so it warms up).

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26
Q

What happens in terms of energy transfer when an object is hotter than its surroundings?

A

It emits more infrared radiation than it absorbs (so it cools down).

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27
Q

Do all objects emit and absorb infrared radiation?

A

Yes

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28
Q

How does an object’s temperature affect the amount of infrared radiation?

A

The hotter the object, the more radiation it radiates in a given time.

29
Q

Explain which surfaces are good emitters and absorbers of infrared radiation.

A
  • Dark, matt surfaces - Good absorbers and good emitters

* Light, shiny surfaces - Poor absorbers and poor emitters

30
Q

How do solar hot water panels work?

A
  • Contain water pipes under a black surface
  • Radiation from Sun is absorbed by the black surface to heat water in the pipes
  • This water can be used for washing or pumped to radiators
31
Q

Describe conduction of heat.

A
  • When heated, particles vibrate faster
  • In a solid, they are packed closely together, so they can collide and pass on this kinetic energy
  • This process continues until the heat is spread all the way through the solid
32
Q

Why do metals conduct heat better than non-metals?

A
  • Metals have some free electrons, while non-metals don’t
  • When heated, the electrons move faster and collide with other particles in the metal
  • Since electrons move freely, this is much faster than transferring energy by passing it between neighbouring atoms
33
Q

Why does conduction happens more in solids than liquids and gases?

A

In solids, the particles are held tightly together, whereas in liquids and gases they are not, so they cannot bump into each other as easily.

34
Q

Why is air good for preventing conduction?

A

It is a mixture of gases, so the particles are far apart and do not collide easily.

35
Q

Describe convection.

A
  • When you heat up a fluid, the particles move faster and move further apart from each other
  • So the fluid expands and becomes less dense
  • The warmer, less dense fluid rises above colder, denser surroundings
  • Cooler fluid moves to take the place of the warm rising fluid -> This creates convection currents
36
Q

Why can’t convection happen in solids?

A

The particles can’t move - they just vibrate on the spot.

37
Q

What type of energy transfer do radiators mostly rely on?

A

Convection

38
Q

How can convection be reduced?

A

The fluid has to be stopped moving - for example: clothes, blankets and cavity wall insulation stop convection.

39
Q

How does condensation happen?

A
  • When a gas cools, the particles slow down and lose kinetic energy.
  • This allows attractive forces to pull them closer together.
  • When the temperature gets cold enough, the gas particles get close enough that condensation can happen.
40
Q

What can be seen coming out of a kettle?

A

First of all, near the spout, there is a small region of invisible water vapour. This soon condenses to form condensed water particles, which can be seen as steam.

41
Q

What is condensation?

A

When a gas turns to a liquid.

42
Q

What is evaporation?

A

When a liquid turns to gas.

43
Q

Where in the liquid can evaporation happen?

A

Near the surface.

44
Q

What factors are needed for a particle to evaporate from a liquid?

A
  • Travelling in the right direction to escape liquid
  • Travelling fast enough to overcome attractive forces
  • Near the surface
45
Q

What happens during evaporation?

A
  • Fastest particles are most likely to evaporate
  • This decreases average speed of the remaining particles and the kinetic energy is decreased
  • This means the temperature of the liquid falls
46
Q

When is evaporation useful?

A

When you sweat, the evaporation cools you down.

47
Q

What factors increase the rate of evaporation?

A
  • Higher temperature
  • Lower density
  • Larger surface area
  • Airflow over surface
  • Lower humidity
48
Q

Why does lower density increase the rate of evaporation?

A

The forces between particles are weaker, so more particles have enough energy to escape the liquid.

49
Q

What factors affect the rate of heat energy transfer?

A
  • Surface area to volume ratio
  • Temperature of object
  • Temperature of surroundings
  • Surroundings being an insulator or conductor
  • Type of material
50
Q

What is a heat sink?

A

A device designed to transfer heat away from an object it is in contact with, such as a compuer component.

51
Q

How do animals control heat transfer?

A 
In cold:
- Hairs stand up to trap layer of insulating air
- Animals have small SA:V ratio
In hot:
- Blood diverted to skin
- Animals have large SA:V ratio
52
Q

What happens to most substances when heated?

A

Their particles gain kinetic energy, move further apart and the substance expands.

53
Q

What is a use of substance expansion?

A
  • Bi-metallic strips are made of two different strips of metals that expand at different rates.
  • This means they bend one way when heated and another when cooled.
  • The can be used in thermostats.
54
Q

Energy can be transferred, stored and dissipated but not…

A

… created or destroyed.

55
Q

What does dissipated mean?

A

When energy is spread out and lost.

56
Q

When is a device useful?

A

When it can transfer energy from one form to another.

57
Q

What is the equation for efficiency?

A

Efficiency = Useful energy out / Total energy in

OR

Effciency = Useful power out / Total power in

58
Q

What are Sankey diagrams used for?

A

Showing how much of the total energy input is being usefully employed compared to how much is being wasted.

59
Q

How can you tell how much energy is useful and wasted by looking at a Sankey diagram?

A

Look at the width of each arrow.

60
Q

What are some methods for reducing heat loss in the home?

A
  • Loft insulation
  • Cavity wall insulation
  • Hot water tank jacket
  • Double glazing
  • Draught-proofing
61
Q

What is the difference between effective and cost-effective home insulation methods?

A
  • Effective methods are the ones that give the biggest annual saving
  • Cost-effective methods are the ones that have the shortest payback time
62
Q

What is cavity wall insulation and how does it prevent heat loss?

A
  • Foam squirted into the gap between bricks
  • Reduces convection and radiation
  • Air pockets reduce conduction
63
Q

What is loft insulation and how does it prevent heat loss?

A
  • Thick layer of fibreglass wool laid out across loft floor

- Reduces conduction and convection

64
Q

What is draught-proofing and how does it prevent heat loss?

A
  • Strips of foam and plastic around doors and windows reduces draughts of cold air
  • Reduces convection
65
Q

What is a hot water tank jacket and how does it prevent heat loss?

A
  • Case attached around hot water tank

- Reduces conduction and radiation

66
Q

What are thick curtains and how do they prevent heat loss?

A
  • Big bits of cloth over the window create an air gap between room and window
  • Reduce convection, conduction and radiation
67
Q

What does a U-value show?

A

How effective an insulator is.

68
Q

What does a high U-value show?

A

The insulator is ineffective.

69
Q

What does a low U-value show?

A

The insulator is effective.

GCSE - Physics (6 decks)

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