1
Q
According to the graph attached, describe what is happening at each letter
A
- In section A, kinetic energy increases a lot, whilst potential energy increases a little
- In section B, kinetic energy remains constant, whilst potential energy increases moderately
- In section C, kinetic energy increases rapidly, whilst potential energy changes very minimally
- In section D, kinetic energy does not change, whilst potential energy increases greatly
- In section E, kinetic energy increases, while potential energy is not changing since its value is at its maximum (zero)
2
Q
What is meant by specific heat capacity?
A
The energy required to raise the temperature of one kilogram of a substance by one kelvin
3
Q
What factors does the increase in temperature of an object depend on?
A
- The amount of heat energy transferred
- The mass of the object
- The specific heat capacity of the material from which the object is made
4
Q
What is meant by heat energy?
A
The total of all kinetic and potential energy of the atoms in an object.
5
Q
What happens to the movement of particles if the heat energy of a substance increases?
A
The particles move faster
6
Q
What can happen as a result of a change in heat energy?
A
A change in the object’s state (e.g. liquid to gas)
7
Q
What is the equation to calculate the amount of heat energy needed to change the temperature of a specific mass of a substance?
A
∆E = mc∆θ
Where:
* ∆E = change in heat energy (J)
* m = mass (kg)
* c = specific heat capacity (J kg-1 K-1)
* ∆θ = change in temperature (K or ºC)
8
Q
How is the thermodynamic Kelvin temperature scale defined?
A
An absolute temperature scale where each degree is the same size as those on the Celsius scale
9
Q
Why do different materials have different specific heat capacities?
A
Due to their molecular structure (in the regard that some energy goes towards rotating and stretching ionic bonds as opposed to increasing the particles speed)
10
Q
Why do different materials have different rises in temperature for the same change in heat energy?
A
Due to the equation, E = mc∆θ, when rearranged for change in temperature, ∆θ = E/mc, we can see that a material with a higher specific heat capacity will result in a smaller rise in temperature than a material with a lower specific heat capacity.
11
Q
What are the material states that specific heat capacity is mainly used for?
A
Liquids and Solids
12
Q
How would materials of a low specific heat capacity interact with heat and electricity?
A
Materials of low specific heat capacities are excellent conductors of heat and good electrical conductors (e.g. copper and lead)
13
Q
How would materials of a high specific heat capacity interact with heat and electricity?
A
Materials with a high specific heat capacity are weaker conductors of heat or electricity, meaning that they are ideal for heating homes as water, for example, remains hot in a radiator for a long time.
14
Q
What is the specific heat capacity of copper and what does this mean in terms of its efficient usages?
A
SHC of copper = 390 J kg-1 K-1
Its low SHC allows it to warm up and cool down quickly as it only takes a small amount energy to change its temperature.
15
Q
What is the specific heat capacity of water and what does this mean in terms of its efficient usages?
A
SHC of water = 4200 J kg-1 K-1
Its high SHC means that it warms up and cools down very slowly as it takes much more energy to change its temperature.
16
Q
While a substance changes state, what does not change?
A
Temperature (remains a constant at its point of state change)
17
Q
What is meant by specific latent heat?
A
The thermal energy required to change the state of one kilogram of a substance without any change of temperature
18
Q
What are the two types of latent heat?
A
- Specific latent heat of fusion (melting)
- Specific latent heat of vaporisation (boiling)
19
Q
What is meant by the specific latent heat of fusion?
A
The thermal energy required to convert one kilogram of solid to liquid with no change in temperature.
This is used when melting a solid or freezing a liquid.
20
Q
What is meant by the specific latent heat of vaporisation?
A
The thermal energy required to convert one kilogram of liquid to gas with no change in temperature.
This is used when vaporising a liquid or condensing a gas.
21
Q
What equation is used to calculate the amount of energy required to melt or vaporise a mass with latent heat?
A
∆E = L∆m
Where:
* ∆E = amount of heat energy to change the state (J)
* L = latent heat of fusion or vaporisation (J kg-1)
* ∆m = change in mass of the substance changing state (kg)
22
Q
What are the values for the latent heat of water in terms of both fusion and vaporisation?
A
SLH of Fusion = 330 kJ kg-1
SLH of Vaporisation = 2.26 MJ kg-1
(Evaporating 1kg of water needs roughly 7x more energy than melting the same amount of ice to form water)
23
Q
Why does it require so much more energy to evaporate a substance like water than to melt the same amount of ice to form water?
A
- When ice melts: energy is required to just increase the molecular separation until molecules can flow freely over each other
- When water boils: energy is required to completely separate the molecules until there are no longer forces of attraction between them, hence this requires much more energy
24
Q
What two forms of energy do the molecules of all substances contain?
A
- Kinetic energy
- Potential energy
25
Why is kinetic energy transferred in molecules of a substance?
Kinetic energy is due to the speed of the molecules and gives the material its temperature.
This is due to temperature being a measure of a substances average kinetic energy:
* At higher temperatures, molecules are moving/vibrating faster (high Ek)
* At lower temperatures, molecules are moving/vibrating slower (low Ek)
* At absolute zero (0K), it is presumed that all molecular motion stops (0 Ek)
26
Why is potential energy transferred in molecules of a substance?
Potential energy is due to the separation between the molecules and their position within the structure.
For example, at a molecules rest position (their "preferred" distance from other molecules), the molecule is in equilibrium and has little to no potential energy. However, if the molecules are pulled apart or pressed together, work is being done against the attractive forces, which is stored as potential energy.
27
What is meant by the internal energy (U) of a substance?
The sum of the kinetic and potential energies of all the molecules within a given mass of a substance
28
In terms of molecules, what happens to the movement of particles if the kinetic energy within a molecule increases?
The particles within the molecule move faster
29
In terms of molecules, what happens to the movement of particles if the potential energy within a molecule increases?
The particles within the molecule move further apart or closer to each other
30
How are particles distributed?
Randomly (meaning they all have different speeds and separations)
31
What is the internal energy (U) of a system determined by?
* Temperature (higher temperature = higher Ek and vice versa)
* The random motion of molecules
* The phase of matter (gases = highest U, solids = lowest U)
* Intermolecular forces between particles (stronger intermolecular forces = higher potential energy and vice versa)
32
How can the internal energy of a system increase?
* Manually doing work on it
* Adding heat to it
33
How can the internal energy of a system decrease?
* Losing heat to its surroundings
* Changing state from gas to a liquid, or a liquid to a solid
34
How do you convert between Kelvin and Celsius?
0K = -273.15ºC
100K = -173.15ºC
(100K - 273.15ºC = -173.15ºC)
35
Is it possible to have a temperature lower than 0K?
No (a temperature in Kelvin will **never** be a negative value)
36
What is meant by absolute zero?
The temperature at which the molecules in a substance have zero kinetic energy.
This means for a system at 0K, it is not possible to remove any more energy from it.
37
How do molecules in a solid object react to heat energy?
Transfers heat energy into kinetic energy which causes the molecules to **vibrate**
38
How do molecules in a gas react to heat energy?
Heat energy is transferred into kinetic energy, which causes the molecules to move quickly around their container
39
Why does the internal kinetic energy not affect the overall movement of an object?
The molecules with the internal kinetic energy and frantically vibrating against cancel each other out and therefore means that we can't see this occuring on the outside, whereas if an object was thrown, it would be easy to see the whole objects movement.
40
How would taking energy away from the molecules of a substance affect its temperature?
It would decrease (meaning that Ek ∝ T [K])
41
What is the kinetic theory of gases?
An explanation that models the thermodynamic behaviour of gases by linking the **microscopic properties** of particles (mass and speed) to **macroscopic properties** of particles (pressure and volume)
42
What is the difference between microscopic and macroscopic?
* Macroscopic view looks at the substance as a whole (can be seen by the naked eye)
* Microscopic view looks at what individual atoms and molecules are doing (can be seen through a microscope or sometimes have to be predicted through calculations)
43
What assumptions are the kinetic theory of gas based on?
* Molecules of gas behave as identical, hard, perfectly elastic spheres
* The volume of the molecules is negligible compared to the volume of the container
* The time of a collision is negligible compared to the time between collisions
* There are no forces of attraction or repulsion between the molecules
* The molecules are in continuous random motion
As the number of molecules of gas in a container is very large, an average behaviour (e.g. speed) is usually considered.
44
What is meant by the mean square speed of the particles in terms of the pressure of an ideal gas equation?
mean square speed = `<`c2`>`
Where:
c = average speed of the gas particles
`<`c2`>` has the units m2 s-2
45
Why do some particles have a negative direction, whilst other particles have a positive direction?
Particles travel in all directions in 3D space, and velocity is a vector
46
What happens to the net value of velocity in a system when there are a large number of particles?
The total positive and negative velocity values will cancel out, and therefore give a net velocity value of 0ms-1 overall
47
Why must velocities of particles be squared in order to find the pressure of the particles' gas?
To ensure that all the values end up positive
48
How do you calculate the average speed of particles in a gas?
Take the square root of the mean square speed:
√`<`c2`>` = crms
This is known as the **root-mean-square** speed.
49
What effect does the change of momentum have when molecules rebound from a wall in a container?
The change in momentum causes a force exerted by the particle on the wall (F = ∆p/∆t).
The forces exerted by these particles on the walls create an average overall **pressure**, since pressure is the force per unit area.
50
How do you derive the equation of the momentum into an equation from which you can calculate the total pressure produced by all molecules (the kinetic theory of gases equation)?
1. Change in momentum as a single molecule hits a wall perpendicularly: ∆p = -mc - (+mc) = -mc - mc = -2mc
2. Calculate the number of collisions per second by the molecule on a wall: time between collisions = distance/speed = 2l/c (where c is simply the velocity of that gas molecule, and not the speed of light)
3. Find the change in momentum per second: F = ∆p/∆t = 2mc/(2l/c) = mc2/l
4. Calculate the pressure from one molecule: pressure = force/area = (mc2/l)/l2 = mc2/l3
5. Calculate the total pressure from N molecules: pressure = Nmc2/l3
6. Account for each molecule having a different velocity: pressure = Nm`<`c2`>`/3
7. Consider the effect of the molecule moving in 3D space by splitting the velocity into its components cx, cy and cz, c2 can be defined using pythagoras' theorem in 3D: c2 = cx2 + cy2 + cz2
8. Since there is nothing special about any particular direction, it can be determined that: `<`cx2`>` = `<`cy2`>` = `<`cz2`>`
9. Therefore, `<`cx2`>` can be defined as: `<`cx2`>` = 1/3 `<`c2`>`
10. Substituting the new values for `<`c2`>` and l3 back into the pressure equation obtains the final equation: pV = 1/3Nm`<`c2`>`
51
What is the equation for the kinetic theory of gases?
pV = 1/3 Nm`<`c2`>`
Where:
p = pressure (Pa)
V = volume (m3)
N = number of molecules
m = mass of one molecule of gas (kg)
`<`c2`>` = mean square speed of the molecules (ms-1)
52
How can the kinetic theory of gases equation be written including density?
* density = mass/volume = Nm/V
* Rearranging the pressure equation and substituting the density: pressure = 1/3 x density x `<`c2`>`
53
What is meant by an ideal gas?
A theoretical gas where particle interactions are ignored and particles are treated as point masses having perfectly elastic collisions.
The assumptions hold up well for many real gases at a range of temperatures and pressures.
54
Which three gas laws are combined to create an equation in terms of pressure, volume, temperature and amount of gas (the **ideal gas law** equation)?
* Charles' Law
* Boyle's Law
* Avogadro's Law
pV = NkT
Where:
* p = pressure (Pa)
* V = volume (m3)
* N = number of molecules
* k = boltzmann constant (1.38 x 10-23 J K-1)
* T = temperature (K)
55
What is an equation for the Boltzmann constant?
k = R / NA
Where:
* k = Boltzmann constant
* R = molar gas constant (8.31 J K-1 mol-1)
* NA = Avogadro's constant (6.02 x 1023 mol-1)
56
What is the value of Boltzmann's constant?
1.38 x 10-23 J K-1
57
What are the units of the Boltzmann constant?
J K-1
This is because the constant relates the properties of **microscopic** particles (such as the kinetic energy of gas molecules) to their **macroscopic** properties (such as temperature)
58
Why is the Boltzmann constant value so small?
The increase in kinetic energy of a molecule is very small for every incremental increase in temperature
59
What properties do the ideal gas laws experiment with?
Relationships between pressure (P), volume (V) and temperature (T) of an ideal gas
60
What properties of ideal gases are assumed to be constant in the gas laws?
The mass and the molecules of the gas
61
What is Boyle's Law?
If temperature (T) is constant:
P ∝ 1/V
**AND**
P1V1 = P2V2
Where:
* P1 = initial pressure (Pa)
* P2 = final pressure (Pa)
* V1 = initial volume (m3)
* V2 = final volume (m3)
62
What is Charles's Law?
If the pressure (P) is constant:
V ∝ T
**AND**
V1/T1 = V2/T2
Where:
* V1 = initial volume (m3)
* V2 = final volume (m3)
* T1 = initial temperature (K)
* T2 = final temperature (K)
63
What is the pressure law?
If volume (V) is constant:
P ∝ T
**AND**
P1/T1 = P2/T2
Where:
* P1 = initial pressure (Pa)
* P2 = final pressure (Pa)
* T1 = initial temperature (K)
* T2 = final temperature (K)
64
Gas molecules inside a container collide with the container walls. What would happen to the gas molecules if temperature is increased?
There would be more frequent collisions of gas molecules with the container wall as the particles have more energy
65
What equation states that Boyle's Law be considered a constant?
pV = constant
66
What is the equation to calculate the cross-sectional area of a circle?
A = (πd2)/4
67
What is the value of atmospheric pressure on Earth?
Atmospheric Pressure = 101kPa
68
How would you derivate the ideal gas equation (in terms of number of molecules) into an equation for average kinetic energy?
1. Recall ideal gas equation: pV = NkT
2. Recall equation linking pressure and mean square speed of the molecules: pV = 1/3 Nm(crms)2
3. This means that: 1/3 Nm(crms)2 = NkT
4. Cancel out N's and multiply by 3 on both sides: m(crms)2 = 3kT
5. Recall kinetic energy equation: EK = 1/2 mv2
6. Instead of v2 for the velocity of one particle, (crms)2 is the average speed for all molecules, so multiplying both sides of the equation by 1/2 gives the average kinetic energy for **one molecule** of the gas: EK = 1/2 m(crms)2 = 3/2kT
7. To find the average kinetic energy for **many molecules** of the gas, multiply both sides of the equation by the number of molecules (N) to obtain: EK = 1/2 Nm(c)2 = 3/2 NkT
69
What is the average kinetic energy equation for one molecule of a gas?
EK = 1/2 m(crms)2 = 3/2 kT
Where:
* EK = kinetic energy of a molecule (J)
* m = mass of one molecule (kg)
* (crms)2 = mean square speed of a molecule (m2 s-2)
* k = Boltzmann constant (1.38 x 10-23 J K-1)
* T = temperature of the gas (K)
70
What is the average kinetic energy equation for many molecules of a gas?
EK = 1/2 Nm(c)2 = 3/2 NkT
Where:
* EK = kinetic energy of a molecule (J)
* N = number of molecules
* m = mass of one molecule (kg)
* (crms)2 = mean square speed of a molecule (m2 s-2)
* k = Boltzmann constant (1.38 x 10-23 J K-1)
* T = temperature of the gas (K)
71
What does the average kinetic energy equation for an ideal gas show kinetic energy to be directly proportional to?
Temperature (K)
EK ∝ T
72
What is meant by black body radiation?
The thermal radiation emitted by **all** bodies (objects) in the form of electromagnetic waves (usually in the **infrared** region on the spectrum, but depends on the temperature).
The hotter the object, the more infrared radiation it radiates in a given time.
73
What is the definition of a perfect black body?
An object that absorbs (or emits) all of the radiation incident on it and does not reflect or transmit any radiation.
74
If a black body is a good absorber, what would that mean about its emission?
It would be a good emitter
75
How would a **perfect** black body emit thermal radiation?
It would be the best possible emitter
76
Why will an object that perfectly absorbs all radiation be black?
The colour black is what is seen when all colours from the visible light spectrum are absorbed.
77
Why are shiny colours good reflectors of radiation?
They are very poor absorbers, and therefore very poor emitters.
78
What properties of distribution of emitted waves depend on the temperature of the body (object)?
* Wave intensity distribution
* Wavelength distribution
As the temperature increases, the peak of the curve moves
79
According to the electromagnetic spectrum, what is the energy of a wave with a smaller wavelength?
Waves with a smaller wavelength have a **higher** energy (e.g. UV rays, X-rays)
80
When an object gets hotter, what happens to the amount of thermal radiation it emits?
It's emission of thermal radiation **increases**. This increases the thermal **energy** emitted and therefore the wavelength of the emitted radiation decreases.
81
What is meant by an ideal black body radiator?
An object that absorbs and emits all wavelengths. The idealised black body is a theoretical object, however **stars** are the best approximation there is.
82
What is the wavelength range for visible light?
350nm to 700nm
83
What is the Stefan-Boltzmann law?
The total energy emitted by a black body per unit area per second is proportional to the fourth power of the absolute temperature of the body.
84
What two factors does an objects luminosity depend on?
* Its surface temperature
* Its surface area
85
What is meant by the luminosity of an object?
The total power output of radiation emitted by a star
86
What is the Stefan-Boltzmann Law equation?
L = σAT4
Where:
* L = luminosity of the star (W)
* A = surface area of the star
* σ = the Stefan-Boltzmann constant (5.67 x 10-8 W m-2 K-4)
* T = surface temperature of the star (K)
87
How can the surface area of a star be calculated?
Using sphere area equation:
A = 4πr2
88
What is the value of the Stefan-Boltzmann constant (σ)?
σ = 5.67 x 10-8 W m-2 K-4
89
What does Wien's Law state?
The black body radiation curve for different temperatures peaks at a wavelength that is inversely proportional to the temperature.
λmax ∝ 1/T
Where:
* λmax is the maximum wavelength (m) emitted by an object at the peak intensity
* T is the surface temperature (K) of an object
90
What is the equation for Wien's Law?
λmax T = 2.9 x 10-3m K
Where:
* λmax = maximum wavelength (m) emitted by an object at the peak intensity
* T = surface temperature (K) of an object
* 2.9 x 10-3m K = Wien's displacement constant
91
What does Wien's Law equation suggest about the **wavelength of a radiation** emitted from a body if it has a high temperature?
The higher the temperature, the **shorter** the wavelength at the peak intensity (therefore **hotter** objects tend to be **white or blue**, and **cooler** objects tend to be **red or yellow**)
92
What does Wien's Law suggest about the **intensity of radiation** at each wavelength if a body has a high temperature?
The higher the temperature, the **greater** the intensity of the radiation at each wavelength
A-Level Physics Edexcel Flashcards
flashcards
Decks in class (15)
# Cards
-
Topic 1 - Working as a Physicist120
-
Topic 2 - Mechanics136
-
Topic 3 - Electricity152
-
Topic 4 - Materials74
-
Topic 5 - Waves & Particle Nature of Light201
-
Topic 6 - Further Mechanics71
-
Topic 7 - Electric & Magnetic Fields217
-
Topic 8 - Nuclear/Particle Physics190
-
Topic 9 - Thermodynamics92
-
Topic 10 - Space79
-
Topic 11 - Nuclear Radiation64
-
Topic 12 - Gravitational Fields60
-
Topic 13 - Oscillations61
-
Command Words2
-
Equations113
