Paper 3 Flashcards
(104 cards)
1
Q
What is a frame reference
A
A set of coordinates to record the position and time of events
2
Q
What does it mean by an inertial frame of reference
A
A reference that is not accelerating
3
Q
What was the idea of absolute motion
A
-the idea that if an object is moving at a particular speed according to one observer, all other observers will observe the same thing
-this has since been rejected
4
Q
What was the ether meant to be
A
A substance that would allow waves to travel through it but it wouldn’t get in the way of rotating bodies
5
Q
What were Michelson and Morley trying to test in their experiment
A
They where trying to measure how much the ether slows down the speed of light
6
Q
What was the purpose of a semi-silvered glass block
A
It allowed some light to pass through and reflect some light
7
Q
Why did they use a plane glass block (compensator)
A
The compensator ensured that both beams of light travelled through the same distances of glass and air.
8
Q
What did the observer see in the Michelson-Morley experiment
A
Light and dark fringes where the two light beams interfere in phase or out of phase
OR
Interference pattern of concentric rings
9
Q
What did michelson and Morley do to the experiment
A
Roatated the apparatus round through 90 degrees
10
Q
What did Michelson and Morley predict
A
The speed of light was thought to change dependent on the speed of the source relative to the ether
If the experiment was rotated through 90 degrees, the fringes would shift because the speed of light along each path would change, the time taken along each path would change and hence the phase difference would change
11
Q
What did Michelson and Morley observe
A
They performed the experiment at different times and at different angles
- However their results only ever showed displacements of the interference project (around 0.02 fringe widths) and not even in the expected orientations
- These values are too small to be significant and was most likely an external factor (Experimental noise).
12
Q
What did Michelson and Morley conclude
A
The Aether doesn’t exist and therefore light is a wave able to travel without a medium
The speed of light is unchanged by the earths motion - IT IS INVARIANT
13
Q
State the two postulates of special relativity
A
- The laws of physics are the same in all inertial frames of reference
- The speed of light, in a vacuum, is the same in all inertial frames of reference
14
Q
Which observer gives the value for proper time
A
The object that is at both events gives the value for proper time
15
Q
The proper time is the ______________ time between the two events
A
Shortest
16
Q
The proper length is always _______________ than the length measured by an observer who is moving relative to the object
A
Longer
17
Q
Which is larger the relativistic mass of a moving object or its rest mass
A
The relativistic mass is greater
18
Q
What equations should not be used in paper 3 only
A
KINETIC ENERGY = 0.5 x m x v^2
19
Q
How do you work out the kinetic energy of you know the total energy and the rest mass
A
The kinetic energy the total energy - rest energy
20
Q
What was bertozzis experiment
A
Bertozzi did an experiment to measure the speed of electrons with different kinetic energies
21
Q
How did Bertozzi accelerate electrons
A
By using a linear particle accelerator to accelerate electrons into the disk (Using different potential differences)
22
Q
How did Bertozzi measure the speed of an electron
A
Speed = s/t
- once the speed was constant
- then calculated the distance between two signals
23
Q
How did Bertozzi know the kinetic energy of electrons
A
qv=Ek
When an accelerating particle with charge q, the work done by an electric field with potential difference = energy gained, Ek
24
Q
What did Bertozzi plot
A
Squared speeds against kinetic energy of electrons
[The data agreed with relativistic predictions]
25
What did Bertozzi find
The results agree closely with the relativistic predictions of speed and show electrons cannot exceed the speed of light
26
What are some safety measures for inverse square law for gamma source experiment
Handle the source with tongs
Minimise exposure time
Stand behind lead screens
Keep source in lead lines box when not in use
27
What is the method for the inverse square law law for gamma source experiment
Measure the background radiation
Put gamma source at set starting distance
Record 3 measurements for each distance- take and average
Repeat for several set distances
28
What do you plot for an experiment for inverse square law for a gamma source experiment
Plot a graph of 1/ root correct count rate against the distance. This is because of a systematic error in x as we are unsure where the gm tube actually counts the gamma.
29
Give three ways charged particles are produced in a discharge tube
High voltage means electron is pulled off gas atoms
Ionisation by collision with atoms
Positive ions near cathode hit cathode and cause it to release electrons (that are accelerated towards anode)
30
Give two ways light is produced in a discharge tube
Near the anode: electrons excite gas atoms (by collisions) and photons are emitted when de-excitation occurs
Near the cathode: ions and electrons (moving in opposite directions) collide and recombine and emit photons
31
In a discharge tube what happened to the the glowing gas near the anode when a magnet was brought near. What does it show.
It was distorted
This shows charged particles are responsible for the glowing gas near
32
What are cathode rays
Rays emitted from the cathode in a discharge tube (has a momentum)
33
How was it concluded that there must be radiation in a discharge tube with a charge moving from cathode to anode
The paddle wheel turned in that direction and when a magnet was brought close it stopped turning
34
Why does the gas in a discharge tube need to be at low pressure
Particles are widely spaced, and ions are accelerated enough in between collisions to cause excitation and ionisation.
If the pressure was too high there are too many particles and the positive ions and electrons only travel a short distance in between collisions
35
What did JJ Thomson prove about the particles in a discharge tube
They all had the same specific charge no matter what the gas was inside the tube.
[Same particles emitted for every gas therefore particles were part of the substructure of matter]
36
If an electron is accelerated from rest through a potential difference , V, what is an equation that could be used to find the speed of the electron
W =VQ ——> 0.5 x m x v^2 = VQ
37
Describe the process of thermionic emission
When a current passing through a filament causes the temperature of the filament to increase enough so that electrons in the filament gain enough kinetic energy to be released.
38
In a fine beam tube why does the helium gas (at low pressure) have to be in the tube
So we can see the path of electrons
39
For the fine beam tube why is the path of the electron beam not a perfect circle
Electrons collide with helium, losing energy (kinetic)
This causes the electron to lose speed
This causes the radius of the circle to decrease
40
What was the significance of Thomsons determination of the specific charge of an electron
Didn’t know what the particle was yet
The specific charge was much larger (~2000x) then the largest specific charge measured to date (that of the hydrogen ion)
[and the same in multiple discharge tubes]
Conclusion: There is a new particle that might have a larger charge or a smaller mass or both
41
What is an equation linking the mass of the droplet m, the charge of the droplet Q, the potential difference between plates V, and the distance between the plate d.
VQ/dg = m
42
Give one way that the oil droplets could be made charged in milikans oil droplet experiment
As the drops pass out of the atomizer they are ionised by an X-ray.
OR
By friction as they come out the atomizer
43
During milikans experiment the drop,etc falls through the air . Use newtons law to describe and explain the motion.
There is a resultant force downward so it accelerates downward (2nd law)
As the speed increases, the drag force increases, the resistive force decreases and the acceleration decreases until drag = weight (terminal velocity)
44
What did Milikans finding tell us
Milikan found out that all the different charges gathered were whole number multiples of 1.6x10^-19
Therefore the charge if each electron is 1.6x10^-19
45
What was Newton's theory of light
Newton's corpuscular theory was the theory that light was particles
46
How did Newton's theory explain reflection
The corpuscles hit the reflective surface and experienced an equal and opposite force from the surface.
This is because the corpuscular theory treated corpuscles like solid, elastic spheres
47
If Newtons theory was true what would the edges of shadows be like
The edges of shadows would be sharp and well-defined with no blurring or diffraction effects.
48
Why, if Newton's theory were true, would the edges of shadows be well defined
Becuase if light were a particle then it wouldnt be able to bend around objects
49
Why was Newtons corpuscular theory preferred over Huygens wave theory
Newton was already a widely respected scientist, so he was preferred
We couldn't measure the speed of light in glass at this point due to the equipment not being as advanced yet
Huygens' theory doesn't explain polarisation
50
What was observed during youngs double slit experiment
A diffraction pattern can be observed:
Parallel slits of bright and dark fringes (of point of cancellation and reinforcement) with a bright central maxima that lost intensity the further from the center it is.
51
What would be observed from Youngs double slit experiment if Newtons theory was true
Particle-like behaviour predicted only two bright regions and therefore cannot account for an interfernece pattern
52
Why was the wave theory of light finally accepted
Because of its ability to explain interference and diffraction, which Newton's corpuscular theory struggled to account for
53
Fizeau gradually ________ the frequency of rotation of the cog from ________, until the light was ________ for the first time. At this point, he knew the light must be hitting the tooth, ________ to the gap that it originally went through.
Increaed
zero
not seen
at an angle
54
What is the phase differnece between the oscillating electric and magnetic fields
Zero/360
The two waves are in phase with each other
55
What are the oscillations of electromagnetic waves like
The electric and magnetic waves oscillate perpendicular to each other and to the direction of energy propagation
56
What did Hertz use to produce and detect radio waves
A high voltage spark gap transmitted radio waves, and the detector received these. The detector is usually an incomplete wire ring which forms sparks across the gap when detecting radio waves.
57
How were the waves reflected in hertzs experiment
He placed a metal screen behind the spurce and measured a stronger sigal with the detector
[This showed that radio waves were reflected off the screen back toward the detector, Causing Superposition.]
58
Define a black body
A body that is a perfect absorber of radiation
59
Define black body radiation
Black body radiation is the name given to the thermal radiation emitted by black bodies
60
For a graph of intensity against wavelength for the radiation emitted from a black body. What is the problem with the curve predicted by using the classical wave theory?
Intensity tends to infinity as the wavelength tends to zero. Therefore, an infinite amount of energy is required.
61
Plancks solution:
________ is emitted in ________ (discrete amounts).
Em radiation
Quanta
62
What is the photoelectric effect
It is the process in which electrons are released from a metal surface when a light source of frequency greater than that of a certain frequency, known as the threshold frequency, is applied.
63
What was a key observation from the photoelectric effect?
>Light rays with a frequency greater than the metal's threshold frequency cause the immediate emission of electrons from the surface.
>The intensity of incident radiation only affected the number of electrons emitted, NOT the energy they leave with
>Photoelectrons have a range of Ek from zero to their maximum value, depending on the type of metal and frequency of incident light
64
What was a problem with the classical theory when it came to the photoelectric effect
>Classical theory said that if low-frequency radiation was aimed at the metal at a high enough intensity, then enough energy would be transferred to remove photoelectrons.
> Classical theory predicted that an electromagnetic wave transferred energy continuously
> Classical theory said that light of any frequency should cause emission
65
Why does radiation below the threshold frequency not cause photoelctrric emission
ONLY ONE PHOTO CAN TRANSFER ITS ENERGY TO ONE ELECTRON.
Therefore, if the photon's energy was not large enough to sufficiently energise the electron, the photons could not combine to energise that electron.
66
The ________ potential differnece that reduces the current to ________ is called the ________ ________
Minimum
Zero
Stopping Potential
67
What was Einstein’s theory of light
Einstein proposed that electromagnetic radiation was made up of discrete quanta, or packets, of energy.
[This theory explained the experimental results of the photoelectric effect]
68
What is the eqaution for the specific charge of an electron when there is both magnetic and electric field [WHITEBOARD WORKING]
Q/m = V / B^2 r d
69
What is the eqaution for the specific charge of an electron when there is no magnetic field [WHITEBOARD WORKING]
Q/M = 2 g d / V t^2
70
In a cathode ray tube what is the work done equal to
QV = 0.5 M v^2
71
What is the eqaution for the specific charge of an electron when there is no electric field [WHITEBOARD WORKING]
Q/m = 2V / B^2 r^2
72
How do you produce cathode rays
The first discharge tubes produced cathode rays from the cathode using a strong electric field to "pull" electrons across the tube
Forming a cathode ray can be made easier by heating the cathode - this is called thermionic emission
73
The potential difference across the photocell is increased from zero. The current decreases. Why
If the p.d. Is increased there be zones a range of voltages
This range of voltages only allow electrons with a low p.d to pass due to the magnetic repulsion
This mean fewer electrons per second will reach T
74
The ________ potential difference that reduces the current to ________ is called the ________ ________
Minimum
Zero
Stopping potential
75
On a graph of current against potential difference across the photo cell what does the number of photoelectrons released depend on
The intensity of electromagnetic radiation
76
What was de broglies hypothesis
All matter like particles have a wave like nature characterised by the de broglie wavelength
77
What would happen to the diffraction pattern if the accelerating potential difference was increased
The diffraction pattern will become more compressed
78
Why will the diffraction pattern become more compressed if the accelerating potential difference is increased.
Because increasing the accelerating voltage leads to higher kinetic energy and thus a shorter wavelength which results in less diffraction.
79
What does TEM stand for
Transmission electron microscope
80
What does SEM stand for
Scanning tunnelling microscope
81
If a microscope has a ___________ resolving power than another this means that the microscope can be used to distinguish between objects that are ___________ together.
The ___________ the wavelength used in the microscope the ___________ the resolving power.
Greater
Closer
Smaller
Greater
82
What are used as lenses in a TEM
Magnetic fields (electromagnetic coils)
83
Why does a TEM use electrons instead of light
To get a shorter wavelength and better resolution
84
What is the purpose of the electron gun in a TEM
The cathode is heated using current, electrons emitted [Thermionic emission]
Electrons accelerates toward the anode and pass through a hole
85
List the three lenses and what order they come in
Condenser lens
Objective lens
Projector lens
86
What is the purpose of the condenser lens
The condenser lens makes the beam parallel
87
What is the purpose of the objective lens
It magnifies the image
HOWEVER
The image is inverted
88
What is the purpose of the projector lens
Magnifies the image
AND
Inverts the image back to the correct image
89
Why does the sample have to be thin in a TEM
So the electron beam can through and electrons are able to diffract with the sample
90
How does the screen work in a TEM
When the electron beam hits the fluorescent screen at the base of the machine then the image becomes visible
91
Gives three types of evidence for light having PARTICLE nature in a TEM
Deflection in the magnetic field
Electrons accelerating through a potential difference
Electrons colliding with the screen
92
Give an example for light having WAVE nature in a TEM
When the electron beam diffracts through the thin sample
93
How would the thickness of the sample in a TEM affect the power
The electrons would lose kinetic energy
>Velocity decreases
This increases the electrons de broglie wavelength
>Longer wavelength, worse resolution
94
How would a lens aberration in a TEM affect the power
Electrons may have slightly different speeds due to thermionic emissions
This is due to passing through different thickness of the same sample so the image would be focused differently by the magnetic field
So the image would not accurately focus
[Different speeds mean different wavelengths, so different amounts of diffraction]
95
How would the Anode voltage in a TEM affect the power
As the voltage increases the speed the electron is released at increases
This means a shorter wavelength due to de broglies hypothesis
This results in an improved resolution
96
What does STM stand for
Scanning Tunnelling microscope
97
If the gap between the surface and the probe was made smaller what affect would this have on the current
The current would increase
This is because the smaller the gap the greater the probability and the greater the number of electrons per second that cross the gap.
98
What type of material does the surface need to be in a STM
A conducting surface
99
DO ONE LINE AT A TIME.
Electrons have a ___________-___________ ___________.
There is a ___________ ___________ that electrons can cross the gap.
Electrons can ___________ across the gap
The ___________ the gap, the greater the probability and the ___________(per second) that cross the gap.
A ___________ ___________ is necessary so electrons cross in ___________ ___________ only.
Electrons transfer ___________ to ___________
Wave like nature
Certain probability
Tunnel
Smaller, More electrons
Potential difference, one direction
Negative, positive
100
For a STM what is mean by the constant current method
Current due to electron transfer is measured
A feedback loop is used to vertically adjust the height of the tip to make sure current is always constant
The position of the tip is changed to keep the distance between the tip and surface constant
The variation of height of the probe tip with time of the tip tells us how the height surface is varying
101
For a STM what is mean by the constant height method
Keep the height constant (and voltage)
As the distance between the probe and the surface changes so will the current
As the current increases this means the distance decreases (Same with other way C D, D ^)
102
Out of which constant method for a STM which is less favourable
Constant height
This is because: if the surface is too high is can make the probe crash into it and break the tip of the probe
If the surface is too low it can become too low to get a reading of current.
103
How wide is the probe in a STM
1 Atom wide
104
What us the timeline of light and wave-particle duality
Newton and Huygens
Youngs double slit
Fizeaus measuring the speed of light
Maxwells theory of EM waves
Hertz discovery of radio waves
UV catastrophe
Plancks Thoery
The photo electric effect
Einsteins soloution
De broglies hypothesis
Electron microscopesn
