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CIE IGCSE Physics > Thermal physics > Flashcards

Thermal physics Flashcards

1
Q

What are 2 distinguishing properties of solids?

A
  1. Have a definite shape

2. Have a definite volume

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2
Q

What are 2 distinguishing properties of liquids?

A
  1. Have no definite shape

2. Have a definite volume

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3
Q

What are 2 distinguishing properties of gases?

A
  1. Have no definite shape

2. Have no definite volume

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4
Q

Describe the molecular structure of solids

A
  1. Strong forces of attraction between particles
  2. Regular pattern
  3. Very close together
  4. Vibrate about fixed positions
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5
Q

Describe the molecular structure of liquids

A
  1. Weaker forces of attraction between particles
  2. No regular pattern
  3. Close together
  4. Slide past each other
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6
Q

Describe the molecular structure of gases

A
  1. Very weak forces of attraction between particles
  2. No pattern
  3. Widely separated
  4. Move randomly at high speeds
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7
Q

What is the effect of an increase in temperature of a gas?

A

The hotter the gas, the faster the molecules move

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8
Q

What causes pressure on the walls of a container?

A
  1. Collision of molecules with the walls of a container

2. Collision applies a force across the surface area of the walls

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9
Q

Explain pressure

A

Change of momentum of the particles striking the walls creating a force

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10
Q

What is Brownian motion?

A

Random molecular bombardment of small particles

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11
Q

What causes Brownian motion?

A

Molecules in a gas/liquid colliding at high speeds with small particles

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12
Q

Describe evaporation

A

The escape of more-energetic molecules from the surface of a liquid

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13
Q

What is the effect of evaporation?

A

Cooling of the liquid

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14
Q

What are 3 factors that influence evaporation?

A
  1. Surface area
  2. Temperature
  3. Draught
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15
Q

How does surface area affect evaporation?

A

A greater surface area results in more area for particles to escape the liquid

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16
Q

How does temperature affect evaporation?

A

High temperatures give particles more energy to escape from the surface of the liquid

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17
Q

How does draught affect evaporation?

A

If the air is less humid, fewer particles are condensing

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18
Q

Why does evaporation result in the cooling of a liquid?

A
  1. Average energy of remaining molecules decreases

2. Temperature of the liquid also decreases

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19
Q

What happens to a body in contact with an evaporating liquid?

A

It cools

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20
Q

State Boyle’s Law

A

For a fixed mass of gas at constant temperature, pressure is inversely proportional to volume

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21
Q

Describe thermal expansion of solids at constant pressure

A

Expand slightly

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22
Q

Why do solids expand slightly?

A

Due to strong bonds holding molecules together

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23
Q

Describe thermal expansion of liquids at constant pressure

A

Expand more than solids

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24
Q

Why do liquids expand more than solids?

A

Due to weaker bonds between molecules

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25
Q

Describe thermal expansion of gases at constant pressure

A

Expand significantly

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26
Q

Why gases expand significantly?

A

Very weak bonds between molecules

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27
Q

Give 2 examples of properties that change when a substance is heated

A
  1. Volume (and density)

2. Electrical resistance

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28
Q

What is a fixed point?

A

A temperature at which some easily identifiable change occurs

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29
Q

What are the 2 fixed points used in a thermometer?

A

Lower point and upper point

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30
Q

What is usually used as the lower point?

A

0 °C

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31
Q

What is usually used as the upper point?

A

100 °C

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32
Q

What is the need for fixed points?

A

To know the temperature without having to measure it directly?

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33
Q

What does a liquid-in-glass thermometer consist of?

A
  1. Thin glass capillary tube
  2. A liquid that expands with temperature
  3. A glass bulb
  4. A scale
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34
Q

What is sensitivity?

A

The ability to detect small changes in temperature?

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35
Q

What 3 factors increase sensitivity?

A
  1. Use a smaller glass bulb
  2. Use a narrower tube
  3. Use a thinner wall
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36
Q

How does using a smaller glass bulb increase sensitivity?

A

It contains less liquid so absorbs more heat in a less time

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37
Q

How does using a narrower tube increase sensitivity?

A

A small change in volume results in the liquid moving a larger distance along the tube

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38
Q

How does using a thinner wall increase sensitivity?

A

Heat is transferred into the to the bulb more easily

39
Q

What is linearity?

A

When a given change in temperature causes the same change in length

40
Q

What is range?

A

The difference between the lowest and highest temperatures a thermometer can measure

41
Q

What are 2 factors that increase range?

A
  1. Use a wider tube

2. Use a larger glass bulb

42
Q

What are 3 characteristics that make a liquid suitable to be used in a thermometer?

A
  1. Low specific heat capacity
  2. Very low melting point and very high boiling point
  3. Expand uniformly over a large temperature range
43
Q

What is used to measure high temperatures?

A

Thermocouple thermometer

44
Q

What is used to measure temperatures that vary rapidly?

A

Thermocouple thermometer

45
Q

What does a thermocouple thermometer consist of?

A
  1. Digital meter
  2. Probes
  3. Constantan wire
  4. Copper wire
  5. Cold junction
46
Q

Describe the use of a thermocouple thermometer

A
  1. Two different metals are joined to form two junctions
  2. Temperature difference between two junctions causes a tiny voltage
  3. This makes a current flow
  4. Digital meter measures current and converts to temperature reading
47
Q

What is the relationship between the temperature difference and current in a thermocouple thermometer?

A

The greater the temperature difference, the greater the current

48
Q

What is internal energy?

A

Kinetic and potential energy of a substance

49
Q

How does an increase of a substance’s temperature affect its internal energy?

A

The hotter the substance’s temperature, the more internal energy it has

50
Q

What is the average temperature of a material related to?

A

Average kinetic energy of the molecules

51
Q

What is thermal capacity?

A

The amount of energy required to raise the temperature of a material by 1 °C

52
Q

What is the formula for thermal capacity?

A

Q = mc

53
Q

Define specific heat capacity?

A

The amount of energy required to raise the temperature of 1kg of a material by 1 °C

54
Q

Describe an experiment to measure the specific heat capacity of a substance

A
  1. Drill 2 holes in the block
  2. Measure the mass of the block
  3. Place the heater in one of the blocks and a thermometer in the other
  4. Use cotton wool to insulate the block
  5. Note the initial temperature of the block and turn on the heater for x seconds
  6. Note the final temperature
  7. Calculate energy transferred using E = power ÷ time
  8. Use the formula Q = mc∆T to find specific heat capacity
55
Q

What is the formula for specific heat capacity?

A

c = Q ÷ m∆T

56
Q

What is the melting point?

A

The temperature at which the substance changes from solid to liquid

57
Q

What is the boiling point?

A

The temperature at which the substance changes from liquid to gas

58
Q

Describe melting and boiling?

A
  1. A substance’s temperature increases as it is heated
  2. As it changes state its temperature remains constant
  3. Energy is used to break bonds between the molecules
59
Q

Describe condensation and solidification

A
  1. A substance’s temperature decreases as it cools
  2. As it changes state its temperature remains constant
  3. Energy is used to form bonds between the molecules
60
Q

What are 2 differences between boiling and evaporation?

A
  1. Boiling occurs at a fixed temperature while evaporation occurs at any temperature
  2. Boiling occurs throughout the whole liquid while evaporation occurs at the surface of a liquid
61
Q

What is latent heat?

A

The energy required to change the state of a substance

62
Q

What is latent heat of fusion?

A

The energy required to change a substance from solid to liquid

63
Q

What is latent heat of vaporisation?

A

The energy required to change a substance from liquid to gas

64
Q

In terms of molecules, what is latent heat?

A

The energy required to break bonds between molecules and change the state of a substance

65
Q

What is specific latent heat?

A

Energy required to change the state of 1kg of the substance

66
Q

Describe an experiment to measure specific latent heats for steam and for ice

A
  1. Measure the mass of the vacuum flask and water
  2. Place the heater in water and switch on the power supply
  3. Start the stopwatch once water starts to boil
  4. Take several measurements of potential difference and current and average
  5. Switch off the power supply and stop the stopwatch after 300s
  6. Measure the mass of the vacuum flask and water
  7. Calculate decrease in mass
  8. Calculate energy transferred using E = Pt
  9. Substitute calculated values into the formula E = mL
67
Q

What is the formula for specific latent heat?

A

E = mL

68
Q

How is thermal energy transferred in solids?

A

Conduction

69
Q

What are good conductors of heat?

A

Metals

70
Q

What are poor conductors of heat?

A

Non-metals

71
Q

What are poor conductors of heat referred to as?

A

Insulators

72
Q

How does conduction occur?

A
  1. Delocalised electrons bump into positive ions

2. This helps to transfer vibrations along the metal

73
Q

Exam tip ; )

A

If a question on heat mentions metal, the answer will probably be to do with conduction.

74
Q

How is thermal energy transferred through fluids?

A

Convection

75
Q

Exam tip ; )

A

Fluids = liquids and gases

76
Q

How does convection occur?

A
  1. Molecules gain energy
  2. Warmer, less dense molecules rise
  3. Cooler, more dense molecules sink
  4. Warmer, less dense molecules cool and so sink
  5. Cooler, more dense molecules gain heat and so rise
77
Q

What is the resulting process called?

A

Convection current

78
Q

Exam tip ; )

A

If a question on heat mentions liquids or gases the answer will probably be about convection.

Heat does not rise (only hot gases or liquids rise).

79
Q

How thermal energy transferred in a vacuum?

A

Radiation

80
Q

What is thermal radiation?

A

Heat transfer by infrared

81
Q

What is infrared a part of?

A

Electromagnetic spectrum

82
Q

What is the effect of surface colour on emission?

A
  1. White is a poor emitter of thermal radiation

2. Black is a good emitter of thermal radiation

83
Q

What is the effect of texture on emission?

A
  1. Dull surfaces are good emitters of thermal radiation

2. Shiny surfaces are poor emitters of thermal radiation

84
Q

What is the effect of surface colour on absorption?

A
  1. Black is a good absorber of thermal radiation

2. White is a poor absorber of thermal radiation

85
Q

What is the effect of texture on absorption?

A
  1. Shiny surfaces are poor absorbers of thermal radiation

2. Dull surfaces are good absorbers of thermal radiation

86
Q

What is the effect of surface colour on reflection?

A
  1. Black surfaces are poor reflectors of thermal radiation

2. White surfaces are good reflectors of thermal radiation

87
Q

What is the effect of texture on reflection?

A
  1. Dull surfaces are poor reflectors of thermal capacity

2. Shiny surfaces are good reflectors of thermal capacity

88
Q

Exam tip ; )

A

Shiny things do not reflect heat (they reflect thermal radiation).

Black things do not absorb heat (they absorb thermal radiation).

89
Q

Describe experiments to show the properties of good and bad emitters

A

Use beakers and boiling water

90
Q

Describe experiments to show the properties

of good and bad absorbers

A

Use conical flasks and a bulb

91
Q

What are 3 factors of radiation emission?

A
  1. Surface area of the body
  2. Surface temperature of the body
  3. Surface colour of the body
92
Q

How does surface area affect radiation emission?

A

Greater surface area causes more radiation to be emitted

93
Q

How does temperature affect radiation emission?

A

Higher temperature cause more radiation to be emitted

94
Q

How does an insulator keep something warm?

A
  1. Insulator contains trapped air, which is a poor conductor of heat
  2. Trapping the air prevents heat transfer by convection
  3. This reduces rate of heat loss from the object

CIE IGCSE Physics (6 decks)

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