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HKDSE Physics > Book 1: Heat and Gases (Ch1-4) > Flashcards

Book 1: Heat and Gases (Ch1-4) Flashcards

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1
Q

What is temperature?

A

Temperature is a measure of the degree of hotness of an object.

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2
Q

What is a feature of fixed points to define a temperature scale?

A

They are easily reproducible.

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3
Q

What are the fixed points for the celcius temperature scale?

A

lower fixed point: ice point (the temperature of melting ice under normal atmospheric pressure)
upper fixed point: steam point (the temperature of steam above boiling water under normal atmospheric pressure)

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4
Q

How is the range between the fixed points divided in the celcius temperature scale?

A

It is divided into 100 equal divisions with each division being called 1°C.

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5
Q

Which property of materials do thermometers make use of?

A

The temperature-dependent properties

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6
Q

How does a liquid-in-glass thermometer work?

A

The liquid inside expand and contract uniformly when temperature changes. The level of liquid risen up from its bulb indicates the temperature measured by the thermometer.

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7
Q

What is meant by calibrating an unmarked thermometer?

A

Marking a scale on a thermometer

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8
Q

How do you calibrate a thermometer by using a practical method?

A
  1. Put the thermometer into a beaker of melting ice (0°C) and mark the liquid level.
  2. Put the thermometer into a beaker of boiling water (100°C) and mark the liquid level.
  3. Divide the length between the two marked points to 10 portions. Each portion stands for 10°C.
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9
Q

How do you calibrate a thermometer by a graphical method?

A
  1. Measure the liquid level when the thermometer is put in melting ice and boiling water.
  2. Draw a graph of length of liquid against the temperature.
  3. Read from the graph or calculate the calibration from a uniform proportion.
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10
Q

What are two advantages and a disadvantage of using a mercury thermometer?

A

advantages: can measure high temperatures up to 357°C, has a quick response to temperature changes
disadvantage: mercury is poisonous.

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11
Q

What are two advantages and a disadvantage of using an alcohol thermometer?

A

advantages: can measure low temperatures down to -115°C, is not poisonous
disadvantage: slow response to temperature changes.

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12
Q

List 6 types of common thermometers.

A

liquid-in-glass thermometer, infra-red thermometer, rotary thermometer, resistance thermometer, thermistor thermometer, liquid crystal thermometer

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13
Q

How does a rotary thermometer with copper and iron bimetallic strip work?

A

When heated, copper expands more than iron, which makes the strip in the thermometer bend, displaying different temperatures.

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14
Q

What are the properties, molecular arrangement, and molecular movement in a solid?

A

properties: fixed volume and shape
arrangement: closely packed fixed in positions
movement: vibrate about a fixed position

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15
Q

What are the properties, molecular arrangement, and molecular movement in a liquid?

A

properties: fixed volume but unfixed shape
arrangement: closely packed but not fixed in positions
movement: move freely

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16
Q

What are the properties, molecular arrangement, and molecular movement in a gas?

A

properties: no fixed volume or shape
arrangement: far apart, not fixed in positions
movement: move freely at high speeds

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17
Q

How can we infer how much kinetic energy a body has?

A

The faster the molecules move in a body, the more kinetic energy it possesses. The molecules move faster at a higher temperature and move slower at a lower temperature. Therefore, the temperature of the body is a measure of the average kinetic energy due to the motion of the molecules in the body.

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18
Q

What is the minimum temperature of a body?

A

Absolute zero (-273°C)

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19
Q

What is internal energy and what is its unit?

A

Internal energy measures the amount of total energy stored in a body in joules(J) or kilojoules(kJ)/megajoules(MJ).

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20
Q

What is the conversion between joules, kilojoules, and megajoules?

A

1MJ=1000kJ=1,000,000J
1kJ=1000J

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21
Q

What are 3 factors that can change the amount of stored internal energy inside a body?

A

Mass, temperature, state of matter

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22
Q

What is heat? Which symbol is used to represent it and what is its unit?

A

Heat is the energy transferred from one body to another as a result of a temperature difference, represented by Q and its unit is joule(J).

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23
Q

What determines the direction of heat transfer?

A

The temperature difference (instead of the internal energy difference)

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24
Q

What is another way to increase the internal energy of a body?

A

Doing work

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25
Q

What is power and what is its unit and formula?

A

Power measures the rate of energy transfer in watt. It equals the energy transferred divided by the time (P=Q/t)

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26
Q

1W=?J

A

1Js^-1 (joule per second)

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27
Q

What is the conversion between watt, kilowatt, and megawatt?

A

1MW=1000kW=1,000,000w
1kW=1000W

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28
Q

What is a common unit for energy and what is its relationship with Joule?

A

kW h (kilowatt-hour)
1kW h=3,600,000J=3.6*10^6J=3600kJ

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29
Q

What can be used to measure the electrical energy supplied to an electrical device?

A

joulemeter (for low-voltage power supplies) or Kilowatt-hour meter (for mains)

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30
Q

What is heat capacity and what is its unit?

A

Heat capacity measures the amount of energy to heat up a body by 1°C. It is measured in J °C^-1

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31
Q

What is the formula for heat capacity?

A

Heat capacity=energy divided by the change in temperature (C=Q/dT\Q=C*dT)

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32
Q

What is specific heat capacity and what is its unit?

A

Specific heat capacity measures the amount of energy to heat up 1kg of a substance by 1°C. It is measured in Jkg^-1°C^-1.

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33
Q

What is the formula for specific heat capacity?

A

Specific heat capacity=Heat capacity divided by unit mass (c=C/m) and the power divided by the change in temperature and the mass (c=Q/dTm\Q=mc*dT)

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34
Q

What is thermal equilibrium?

A

Thermal equilibrium occurs when two bodies of different temperature are put in contact, and when the bodies reach the same temperature (heat transfer stops)

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35
Q

What is the law of conservation of energy and what can be inferred from it about heat transfer, assuming that there is no loss of energy to the surroundings?

A

Energy cannot be created or destroyed. The total amount of energy in a closed system is conserved. Therefore, in the process of heat transfer, the energy lost by the hotter body is equal to the energy gain by the colder body.

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36
Q

List 3 usages of water making use of its high specific heat capacity.

A
  1. Water coolant: water is used to cool motor cars, power stations, and spacesuits/cooling vests
  2. regulating body temperature: 60%-70% of our bodies is made up of water, helping our body temperture tog stay constant when the temperture of the surroundings change.
  3. Climatic effect: coastal areas have milder seasons compared to inland areas.
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37
Q

What does a substance undergo when it’s temperature is at the melting point? Does it absorb or give out energy?

A

Fusion (melting), which is meant by the change of state of matter. The substance absorbs energy in fusion.

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38
Q

Why does a bottle of melting ice feel colder than a bottle of water (both at 0degrees Celsius) after being held for a while?

A

Both the melting ice and the cold water absorb energy from the surroundings. However, the energy absorbed by the ice are used for it to change its state, so it’s temperature does not increase. Meanwhile, the energy absorbed by the water is used to change the temperature of the water.

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39
Q

What is latent heat?

A

Latent heat means hidden heat, which is the heat absorbed by a substance during its change of state.

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40
Q

What is the name of the process of a substance changing from liquid state to gas state?

A

Boiling, which is a type of vaporisation.

41
Q

What is the shape of a heating curve?

A

The curve consists of first a concave down increasing part, and a concave up increasing part. (The substance heats up, stops temperature change when changing its state, and keeps heating up.)

42
Q

What is the shape of a cooling curve?

A

The cooling curve is joined by a concave up decreasing graph and a concave down decreasing graph. (The substance cools down, stops temperature change when it changes its state, then keeps cooling down.)

43
Q

What is called when a substance changes its state from liquid state to solid state? What is the property of the period of change of state?

A

Solidification. The substance releases latent heat but it’s temperature does not change because it is changing its state.

44
Q

What is the name of the process of a substance changing from gas state to liquid state? Is energy absorbed or released?

A

Condensation, the energy (latent heat) is released by the substance

45
Q

What are the names for the types of energy corresponding to the conversion between solid and liquid states, and liquid and gaseous states respectively?

A

Solid and liquid states: latent heat of fusion
Liquid and gaseous states: latent heat of vaporisation

46
Q

What is specific latent heat?

A

Specific latent heat of a substance is the amount of energy transferred by heating to change the state of 1kg of the substance without a change in temperature.

47
Q

What is the formula and unit for specific latent heat?

A

Latent heat is equal to the heat given out divided by the mass of the substance (l=Q/m). It is measured in J*kg^-1.

48
Q

What is the specific latent heat of fusion of ice?

A

3.34*10^5 J kg^-1

49
Q

What is the the definition and the specific latent heat of vaporisation of water?

A

The specific latent heat of vaporisation of water is the energy needed to change 1kg of water into steam without changing its temperature. It is equal to 2.26*10^6 J kg^-1.

50
Q

What is meant by the conduction of heat?

A

Heat is transferred from an object to another through direct contact.

51
Q

List 3 good heat conductors and 3 good heat insulators.

A

Conductors: copper, silver, aluminum
Insulators: water, wood, air

52
Q

What are some examples of conduction and insulation in daily life?

A

Maintaining temperature: feathers, fur, and fat are good insulators of heat. They help to keep animals warm in winter.
Cooking: utensils are made of good hesat conductors to cook effectively, and their handles are made of heat insulators like wood or plastic to allow users to grasp the utensils easily.
Building: some buildings are lined with foam boards on thier walls to reduce heat gain in summer/heat loss in winter.
Holding food: foam containers are used because of their insulating property.

53
Q

How can conduction of heat in non-metallic solids be explained?

A

In solids, the particles are packed together closely. When a part of a solid is heated, the particles vibrate faster, and they hit neighbouring particles to make them vibrate faster as well.

54
Q

Why are non-metallic liquids and gases worse conductors when compared to solids?

A

The particles of liquids are packed irregularly, and the particles of gases are far apart, which makes the conduction process inefficient as the vibration of hotter particles cannot induce the vibration of neighbouring particles effectively.

55
Q

How can the conduction of heat in metals be explained using the particle model?

A

Atoms consist of a nucleus and electrons. In metals, the outermost electrons in atoms are loosely held, which makes them free elctrons that can move at high speeds when heated. When a part of the metal is heated, both the particles and free electrons move faster, making it more efficient to conduct the heat to other parts of the metal.

56
Q

What is convection?

A

Convection is the process of heat transfer through the movement of the fluid (liquid or gas) itself.

57
Q

What is the convection current of water when it is heated?

A

The water at the bottom is heated first. The heated water expands and becomes less dense. Then the cold water sinks because of its higher density, and it replaces the hot water. Therefore, the cold water can also be heated, and the water is heated.

58
Q

What are some examples of convection in daily life?

A

Convection heaters/ACs: heaters are placed near the floor. The air is warmed and cold air sinks, making it heat the whole room effectively. (vice versa for the example of air conditioner)
Sea-land breezes: Sea breezes and land breezes are caused by convection due to the different specific heat capacity of the land and sea.
Candle flames: they always point upward due to convection.
Extractor hood: it is used in kitchens to remove smoke and steam. It is placed above the stove because hot smoke rises in convection.
Water heating: the heating element is commonly placed at the bottom of the kettle, making heating more efficient because it makes use of convection currents.

59
Q

Why must the heat transfer from the sun to the Earth be done by radiation?

A

There is a vacuum between the Earth and the sun, meaning that there are no particles and therefore neither conduction or convection can transfer the heat.

60
Q

What is radiation?

A

Radiation is a process of heat transfer which does not require any medium or particles. It takes place in all directions.

61
Q

Does everything emit or receive radiation?

A

Yes, everything is both an absorber and a radiator or radiation.

62
Q

Does a colder object have a net gain or loss of radiation?

A

It has a net gain of radiation, and therefore its temperature increases. (vice versa for an object hotter than the surroundings)

63
Q

Under what condition does an object have no net gain or loss of radiation?

A

When its temperature is the same as that of the surroundings.

64
Q

Which types of surfaces are poor absorbers and poor radiators of radiation? Which types of surfaces are good absorbers and radiators of radiation?

A

Poor absorbers/radiators: shiny, light-coloured surfaces
Good absorbers/radiators: dull, black surfaces

65
Q

What are some examples of radaition in daily life?

A

Vacuum flasks/cookers: the surfaces/materials of vacuum containers are usually shiny and steel to reduce heat loss of foods due to radiation.
Greenhouses: The other radiation waves from the sun are converted to infra-red radiation gien out by the warm objects inside. Since glass can trap infra-red radiation, it makes the greenhouse wam.
Cookers/heaters: some of them use infra-red radiation to transfer heat, and the heaters have higher efficiency conpared to the convection heaters because less energy is needed.

66
Q

What is pressure and what is its unit?

A

Pressure measures the normal (perpendicular) force exerted on a surface per unit area. It is measured in pascal (Pa).

67
Q

What is the formula for pressure?

A

Pressure=normal force on a surface/area of the surface=F/A

68
Q

1Pa=?N

A

1Pa=1N M^-2 (newton per square meter)

69
Q

What is atmostpheric pressure?

A

Atmospheric pressure is the force from the atmosphere around us, which acts on all surfaces exposed to the atmosphere, including our bodies.

70
Q

What is the unit for atmospheric pressure and what is its relationship with Pa?

A

atm, 1atm=100 kPa=atmospheric pressure at sea level

71
Q

What tool is used to measure gas pressure and how does it work?

A

Bourdon gauge. It has a curved metal tube which uncoils when pressure is applied, which moves the pointer around a dial.

72
Q

What is Boyle’s law?

A

Boyles’ Law states that for any gas with a fixed mass and temperature, its pressure is inversely proportional tro its volume

73
Q

If the pressure of a gas becomes k times the original pressure, and the temperature stays constant, what is the new volume of the gas in relation to the original volume?

A

The volume will become 1/k of the original volume.

74
Q

What is the shape of a graph plotted against the pressure and temperature of a gas? Where does the graph cut the x-axis (temperature axis)?

A

It is a linear graph with x-intercept at -273.15°C (absolute zero).

75
Q

What is the kelvin temperature scale in relation with the celcius temperature scale?

A

273 kelvin=0°C, 0 kelvin=-273°C

76
Q

What is another name for the kelvin temperature scale? Why?

A

It is also called absolute temperature scale, because 0 kelvin=absolute zero

77
Q

What is the pressure law?

A

For a gas with fixed volume and mass, its pressure is directly proportional to its kelvin temperature.

78
Q

What is the shape of a graph plotted against the volume and temperature of a gas? Where does the graph cut the x-axis (temperature axis)?

A

It is a linear graph with x-intercept at -273.15°C (absolute zero)

79
Q

What is Charles’ law?

A

Charles’ law shows that for a gas with fixed mass and pressure, its volume is directly proportional to its kelvin temperature.

80
Q

What can be inferred from Boyle’s law, the pressure law, and Charles’ law?

A

The product of the pressure of a gas and its volume is directly proportional to its temperature, or pV/T=constant.

81
Q

How many molecules are there in a mole?

A

6.02*10^23 (Avogadro’s number)

82
Q

What is the general gas law?

A

pV=nRT, where n is the number of moles of molecules in a gas

83
Q

What is R in the general gas law?

A

R is called the universal gas constant, which is found to be 8.31 J mol^-1 K^-1

84
Q

What is an ideal gas and how can a real gas behave like an ideal gas?

A

An ideal gas is a gas that oberys the general gas law. A real gas behaves like an ideal gas at low pressures and high temperatures.

85
Q

What does the kinetic gas theory state?

A

Gas molecules are in random motion all the time.

86
Q

What are the assumptions of molecules in an ideal gas?

A
  1. All molecules have the same mass and are identical.
  2. All molecules are in continuous random motion.
  3. There is a large number of molecules in the container.
  4. The size of the molecules are negligible compared with the separation between them.
  5. The duration of collisions are negligible compared with the time between collisions.
  6. The collisions of the molecules themselves/with the container are perfectly elastic.
  7. Intermolecular forces are negligible.
87
Q

In which conditions do the gas satisfy the assumptions of the ideal gases?

A

When the temperature is high (well above its boiling point) and pressure is low.

88
Q

What is the change in gas pressure when there is a change in momentum?

A

When there is a higher momentum, the gas pressure increases.

89
Q

What is the relationship between pressure, volume, mass, and velocity in an ideal gas?

A

pressurevolume=1/3mass*mean square value of velocities
pV=1/3Nm(msv.c^2)

90
Q

What is the total kinetic energy in one mole of gas?

A

3/2RT

91
Q

What is the average kinetic energy of a molecule?

A

3RT/2Na(where Na denotes the number of molecules in one mole of gas)

92
Q

Why can we infer the amount of total KE of gas molecules from their temperature?

A

Shown from the equation KEavg=3RT/2Na, temperature (in kelvin) is directly proportional to the average KE.

93
Q

What is the molecular potential energy for ideal gases? What does this tell about the total internal energy of an ideal gas?

A

There is no potential energy for an ideal gas from the assumptions. Therefore, the total internal energy of an ideal gas is given by its total kinetic energy=3/2nRT.

94
Q

What is the root mean square speed of gas molecules and how can it be caluclated?

A

The root-mean-square speed (rms) is the typical speed of molecules, calculated by taking the square root of (msv.c^2). rms.c=sqrt(3pV/Nm)=sqrt(3RT/mNa)

95
Q

What is Nm and mNa in calculating the rms.c?

A

Nm: total mass of the gas
mNa: molar mass of the gas

96
Q

How can a mechanical simulator simulate Boyle’s law?

A

When the voltage is unchanged, and when the weight of the piston is increased, the height of the piston decreases, which simulates what happens when the temperature is constant but the pressure increases. This results in a decrease in volume, simulating Boyle’s law.

97
Q

How can a mechanical simulator simulate the pressure law?

A

When the voltage is increased, and the height of the piston is unchanged, the weight of the piston increases, which simulates what happens when the temperature rises and the volume stays constant. This results in an increase in pressure, simulating the pressure law.

98
Q

How can a mechanical simulator simulate Charles’ law?

A

When the voltage is increased, and the weight of the piston is unchanged, the height of the piston increases, which simulates what happens when the temperature rises and the pressure stays constant. This results in an increase in volume, simulating the Charles’ law.

99
Q

How can a mechanical simulator simulate the relationship between volume and the number of molecules?

A

When the voltage and weight of the piston ar eunchanged, but more ball bearings are added to the simulator, the height of the piston increases, which simulates what happens when the temperature and pressure is constant but more gas molecules are added. This results in an increase in volume, simulating the relationship between volume and the number of molecules.

HKDSE Physics (8 decks)

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