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LAET A-level OCR Physics A 2024 > Thermal Physics > Flashcards

Thermal Physics Flashcards

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1
Q

What is the specific heat capacity (c) of a material?

A

The energy needed to raise the temperature of 1kg of the material by 1 degree Celsius/Kelvin without any change of state

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2
Q

What are the units of specific heat capacity (c)

A

J kg⁻¹ K⁻¹

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3
Q

How do you calculate the total energy supplied to an electrical heater.

A

W = IVt

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4
Q

What is the specific heat capacity of water?

A

4200 J kg⁻¹ K⁻¹

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5
Q

What is the specific latent heat of vaporisation (L) of a substance?

A

The energy required to change 1kg of a liquid to a gaseous state with no change in temperature

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6
Q

What is the specific latent heat of fusion (L) of a substance?

A

The energy required to change 1 kg of solid to liquid with no change in temperature.

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7
Q

What are the units of specific latent heat (L)?

A

J kg⁻¹

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8
Q

When would you use the equation ∆Q = mc∆T + mL?

A

If an object changes temperature and changes state during heating.

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9
Q

What is the internal energy of a substance?

A

The sum of the randomly distributed kinetic and potential energy of the particles in an object

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10
Q

What is thermal equilibrium?

A

When two objects at the same temperature so no heat flows between them.

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11
Q

What is the relationship between absolute temperature and the average KE of particles in a substance?

A

Absolute temperature is proportional to average kinetic energy of the particles in a substance.

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12
Q

What is the triple point of a substance?

A

The temperature and pressure at which a substance can exist in all three phases in thermal equilibrium.

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13
Q

Describe the kinetic model of a solid.

A

A regular arrangement of particles that are strongly attracted to each other. Particles vibrate around fixed positions.

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14
Q

Describe the kinetic model of a liquid.

A

Particles are attracted to each other but are able to move relative to each other (flow)

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15
Q

Describe the kinetic model of a gas

A

Particles are far apart and there are no forces of attraction between them. They occupy the volume of the whole container.

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16
Q

Why doesn’t the temperature of a substance change whilst it is changing state?

A

The electrostatic potential of the particles is changing rather than the kinetic energy

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17
Q

Why is the electrostatic potential energy of liquids and solids negative?

A

Energy must be supplied to the substance to break the bonds between particles.

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18
Q

What effect does increasing the temperature have on the particles in a substance?

A

t increases their average kinetic energy

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19
Q

What is Brownian motion?

A

The random motion of small particles such as pollen grains or smoke particles suspended in a fluid.

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20
Q

What causes Brownian motion?

A

The collisions between the individual atoms/molecules and the smoke/pollen particle transfer momentum

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21
Q

What is the conclusion from Brownian motion?

A

Particles that make up a fluid/gas are much smaller than the pollen/smoke particle and are in rapid, random motion.

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22
Q

What is Avogadro’s constant?

A

A number of particles equal to the number of atoms in 12 grams of carbon-12

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23
Q

What is one mole of a substance?

A

An amount in which the number of atoms/molecules is equal to Avogadro’s constant.

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24
Q

What is the molar mass of a substance?

A

The mass of one mole of a substance.

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25
Q

How do you find the mass of one atom from its nucleon number?

A

Multiply nucleon number by the atomic mass unit (u) in kg.

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26
Q

How is the atomic mass unit defined?

A

It is 1/12th the mass of a Carbon-12 atom

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27
Q

How do you calculate the number of particles from the number of moles of a substance?

A

Number of particles = number of moles × Avogadro’s constant

28
Q

How do you find the molar mass of a substance from the molecular mass.

A

Molar mass = Molecular mass x Avogadro’s Number

29
Q

How do you find the total mass of a substance from the number of moles?

A

number of moles x molar mass

30
Q

How do you calculate the number of moles of a substance from the number of particles?

A

Number of particles÷Avogadro’s number

31
Q

How do you find the molar mass of an element from its nucleon number?

A

Molar mass is equal to nucleon number in grams.

32
Q

Boyle’s law: Pressure is inversely proportional to…

A

Volume for a fixed mass of gas at constant temperature

33
Q

Charles’ law: Volume is proportional to…

A

Absolute temperature for a fixed mass of gas at constant pressure.

34
Q

Gay Lussac’s Law: Pressure is proportional to…

A

Absolute temperature for a fixed mass of gas at constant volume

35
Q

Avogadro’s law: Volume occupied by a gas is proportional to…

A

Number of particles/moles if pressure and temperature are constant.

36
Q

How do you find absolute zero from a pressure temperature graph?

A

Extrapolate the line to find the x-intercept.

37
Q

What is R in pV = nRT?

A

Molar Gas Constant

38
Q

What is N in pV = NkT?

A

Number of particles

39
Q

What is n in pV = nRT?

A

Number of moles

40
Q

What is k in pV = NkT?

A

Boltzmann constant

41
Q

What units of temperature should be used in the ideal gas equation?

A

Kelvin

42
Q

What is the equation of state for an ideal gas?

A

pV = NkT OR pV = nRT

43
Q

What is an ideal gas?

A

A theoretical gas that obeys the gas laws at all pressures and temperatures

44
Q

What are the SI units of pressure?

A

Pascal (Pa or Nm⁻²)

45
Q

What is the definition of pressure?

A

The force per unit area exerted normally to a surface

46
Q

What is the relationship between root mean square speed of particles in a gas and absolute temperature?

A

rms speed is proportional √(absolute temperature)

47
Q

Why does increasing the temperature of an ideal gas increase pressure?

A

Particles have greater kinetic energy so there is a greater rate of collisions and greater change in momentum per collision.

48
Q

Why does increasing the volume of an ideal gas decreases pressure?

A

P=F/A. Force exerted decreases as the rate of collisions with the container decreases and the surface area increases.

49
Q

According to Newton’s second law if a particle experiences a change in momentum…

A

There must be a force acting on the particle.

50
Q

According to Newton’s third law if a container exerts a force on a particle…

A

The particle must exert a force on the container.

51
Q

How do you calculate the mean square speed of gas particles from their velocity?

A

Square the magnitude of the velocity of each individual gas molecule and then take the mean average of these values.

52
Q

How do you calculate root mean square speed of a gas?

A

Square the magnitude of the velocity of each individual gas molecule, take the mean average of these values and then take the square root.

53
Q

Why is root mean square speed used instead of velocity?

A

Average velocity is zero.

54
Q

What is N in pV = ¹/₃ N m (c)²

A

Number of particles

55
Q

What is (c)² in pV = ¹/₃ N m (c)²

A

Mean square speed

56
Q

What is ³/₂kT equal to?

A

The mean kinetic energy of one gas particle

57
Q

What form is the internal energy of an ideal gas?

A

Purely kinetic (i.e. no potential energy)

58
Q

Why is there no potential energy in an ideal gas?

A

Becuase there are no force between particles (except during collisions).

59
Q

What is ³/₂NkT equal to?

A

Total internal energy of an ideal gas.

60
Q

Kinetic theory assumption concerning volume

A

The volume of the particles in a gas is negligible compared to the volume of the container

61
Q

Kinetic theory assumption concerning forces

A

There are no electrostatic forces between particles except during collisions

62
Q

Kinetic theory assumption concerning motion

A

Particles are in continuous, rapid, random motion.

63
Q

Kinetic theory assumption concerning collisions

A

The collisions particles undergo with each other and the container are all elastic

64
Q

Kinetic theory assumption concerning time

A

The duration of collisions is negligible compared to the time between collisions

65
Q

What is the relationship between absolute temperature and the average KE of particles in a substance?

A

Absolute temperature is proportional to average kinetic energy of the particles in a substance.

LAET A-level OCR Physics A 2024 (16 decks)

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