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Physics A-level Paper 2 > Topic 9: Thermodynamics > Flashcards

Topic 9: Thermodynamics Flashcards

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1
Q

What is the definition of Internal energy?

A

Internal energy/heat is the sum of kinetic energy and potential energy for all molecules.

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2
Q

How does internal energy change when a substance changes state?

A

Internal energy also changes. KE stays the same so heat energy is transferred to potential energy.

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3
Q

What happens when Kinetic/Potential energy of molecules increase?

A

Kinetic increase
- Molecules move faster
Potential increase
- Particles move further/closer to each other

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4
Q

What is the definition of temperature?

A

Temperature is the average kinetic energy of the particles in a material.

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5
Q

What is the absolute scale of temperature measured in?
How do you convert from degrees to absolute scale?

A

Absolute scale of temperature is measured in kelvins.
To get from degrees to kelvin, add 273.15K.

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6
Q

What is absolute zero?

A

Absolute zero is when temperature is 0 kelvin
Particles have:
-Zero Kinetic energy
-Exert zero pressure
-No volume

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7
Q

What is the specific heat capacity?

A

Specific heat capacity is
-the amount of energy needed
-to raise temperature of 1kg of a substance
-by 1 kelvin

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8
Q

What is the formula for specific heat capacity?

A

Change in energy = mass x specific heat capacity x change in temp

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9
Q

How does internal/kinetic energy change during a change in state of a substance?

A

The internal energy changes but the kinetic energy (and temperature) doesn’t.
This is because the energy is transferred to potential energy to help break the bonds of the particles.

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10
Q

What is specific latent heat?

A

Specific latent heat is:
-Amount of energy needed
-for 1kg substance
-to change state

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11
Q

What are the two types of specific latent heat and what is the difference?

A

Specific latent heat of vapourisation —> between gas and liquid
Specific latent heat of fusion —> between solid and liquid

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12
Q

What is the formula for specific latent heat?

A

energy = mass x latent heat of fusion/vapouristaion

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13
Q

What is an ideal gas?

A

Ideal gases do not have forces between particle therefore particles have no potential energy, only kinetic energy.

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14
Q

What are the 5 assumptions of ideal gases?

A
  • All molecules act as identical, hard shapes
  • V of molecules is negligible compared to V of container
  • Time of collision is negligible compared to time between collisions
  • No forces of attraction/repulsion between molecules
  • Molecules are in continuous random motion
  • Collisions are all elastic
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15
Q

What does the gas law of Boyle’s Law state?

A

For a constant mass of gas at a constant temperature:
- the PRESSURE exerted is INVERSELY proportional to the VOLUME
- P =k x 1/v

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16
Q

What does the gas law of Charles Law state?

A

For a constant mass at constant pressure:
- The VOLUME occupied is PROPORTIONAL to its ABSOLUTE TEMPERATURE
- V = kT

17
Q

What does the gas law of Pressure Law state?

A

For a constant mass and constant volume:
- The PRESSURE exerted by the gas is PROPORTIONAL to the ABSOLUTE TEMPERATURE
- p = kT

18
Q

What do the gas laws combine to give?

A

Gas laws can be combined to give equation - pv/T = constant

The constant in the equation depends on the amount of gas present which is equal to Nk
N - number of molecules
K - Boltzmann’s constant 1.38x10^-23

Plugging Nk into the equation gives:
pV/T = Nk
pV = NkT

19
Q

What is a black body radiator?

A

A black body radiator is a perfect absorber and emitter; absorbs and emit all frequencies of EM radiation.

20
Q

What are two laws/formulas used with black-body radiation?

A

Stefan-Boltzmann Law
L = σAT^4
Wien’s Law
λmax x T = 2.989x10^3 mK

21
Q

What do all objects with a temperature above absolute zero emit?

A

Objects above absolute zero emit energy in the form of EM radiation.

22
Q

What is Lambda max?

A

The point of Lambda max will be at the wavelength at which it emits the largest intensity of radiation.

23
Q

What does the wavelength and intensity of radiation depend on?

A

Both wavelength and intensity depend on temperature of the black body.

24
Q

What is the relationship between the temperature, intensity and the wavelength?

A

As the object gets hotter, it emits more short wavelength radiation and intensity of radiation increases

25
Q

Which objects produce a visible light?

A

Objects that are very hot

26
Q

What does Stefan-Boltzmann law state?

A

Stefan’s Law states that Luminosity ,L of a blackbody radiator (power output) is directly proportional to its surface area (A) and its absolute temperature (T).

L = σAT^4
σ = Stefan-Boltzmann’s constant (5.67x10^-8)

L=4πr^2 x σ x T^4

27
Q

What does Wien’s displacement law state?

A

Wien’s law states that peak wavelength of emitted radiation from black body is inversely proportional to its absolute temperature.

28
Q

What is the formula for Wien’s law?

A

λmax x T = 2.989x10^3 mK

λmax = max wavelength
T = Temperature in K
mK = meters Kelvin

29
Q

Explain why pressure increases when the air is heated in a container of fixed volume. (4)

A
  • Increased temp causes increased average KE of molecules
  • Molecules have greater speed ; collision rate with walls greater
  • Rate of change momentum during collision increases
  • Causes greater force to be exerted on wall, increasing pressure
30
Q

How does heat affect density of air?

A
  • Increased heat means avg KE of air molecules increase
  • Creates expansion effect, decreasing density
31
Q

Explain, using ideas of momentum, why pressure exerted by a gas increases as the temperature of the gas increases.

A
  • As temp increases, avg KE increases
  • Greater speed so momentum of atom increases
  • Rate of collisions of atoms with container walls increases
  • Rate of change of momentum at the walls increases
  • Rate of change of momentum is equal to force
  • Pressure is F/A and force is greater

Physics A-level Paper 2 (7 decks)

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