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Paper 3 > Turning points > Flashcards

Turning points Flashcards

1
Q

What happens when a P.d is applied across a Discharge Tube? What must the Tube have?

A

The tube will begin to glow, glowing brightest at the cathode. The glow is called a Cathode Ray. The tube must have a low pressure gas inside it

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2
Q

What did Thomson show about Cathode Rays? (4)

A
  • Have a mass
  • Have a negative charge
  • Have the same properties no matter what gas is used
  • Have a very large charge to mass ratio
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3
Q

What were Cathode Rays renamed to and what was discovered about them?

A

Electrons. All atoms contained them

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4
Q

What is the process where a Discharge Tube Glows? (4)

A

1) High p.d across tube pulls electrons off gas atoms. Forming ion and electron pairs
2) Positive gas ions accelerate towards cathode and release more electron
3) Electrons accelerate down the tube (low pressure = high speed) and collide with gas atoms, exciting them
4)Atoms de-excite, releasing light photons

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5
Q

Why is the glow brightest at the Cathode?

A

Here the gas ions and electrons can recombine and emit light photons

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6
Q

What is Thermionic Emission?

A

Where a metal is heated until the free electrons on its surface gain enough energy and are emitted

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7
Q

How does an Electron Gun work?

A

P.d is applied to cathode which is heated and releases electrons. Electrons accelerate towards anode, which has a small gap. Electrons that pass through this gap from a narrow beam which travels at a constant velocity.

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8
Q

What is 1 eV equal to?

A

The kinetic energy of an electron accelerated across a potensial difference of 1V

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9
Q

How does a Fine Beam Tube work? (4)

A

1) Apparatus contains a low pressure gas with uniform magnetic field passing through
2) Electrons are accelerated using an electron gun and enter the tube perpendicular to the field direction
3) The magnetic field field makes the electrons move in a circular path
4)As the electrons move through the tube, they collide with gas atoms, exciting them and then de-exciting to produce light which means their path is visible so the radius of their path can be measured

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10
Q

What is the equation for specific electron charge?

A

e / m_e = 2v / (B^2 r^2 )

Electron charge (e), Electron mass (m_e), p.d (V), Field strength (B),
Radius of tube (r)

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11
Q

Why was Thomson’s determination of Specific Charge significant?

A

It showed that specific charge was constant whatever gas was used, which showed that all atoms contained electrons

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12
Q

How does Millikans droplet experiment work?

A

1) An atomiser sprays droplets of oil (negative due to friction) which fall until they reach 2 parralell plates
2) The 2 plates form an electric field and because the droplets are charged, they experience a force

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13
Q

How can the strength of the electric field in Millikans experiment be changed and what affect does this have?

A

The strength can be adjusted by changing the p.d between the plates until the observed droplet becomes stationary meaning ITS WEIGHT IS EQUAL TO THE ELECTRIC FORCE UPWARDS (EQ = mg)

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14
Q

How do you measure the mass of a droplet?

A

1) Remove the p.d so the droplet no longer experiences a force and begins to fall
2) The droplet will experience a resistive force upwards (viscous drag force)

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15
Q

What equations can be used to measure viscous drag force?

A

F=6πηrv

Force (F), Viscosity of fluid (η), Radius of object (r), terminal velocity (V)

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16
Q

What did millikan’s results show?

A

The charge of all droplets where always mulitples of 1.60 x10^-19

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17
Q

What was newtons corpuscular theory of light?

A

light was formed of tiny particles called corpuscles

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18
Q

how did newton explain reflection?

A

corpuslces collide with the surface and a repulsive force pushes the back. The perpendicular velocity changes direction, the parralel velocity stays the same

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19
Q

How did newton explain refraction?

A

as the corpuscle approaches a denser medium, short-range forces of attraction cause the perpendicular velocity to increase but the parrallel velocity stays the same. therefore its direction changes

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20
Q

What was huygens theory of light?

A

He believed that light was a wave and that every point on a wavefront is a point source to secondary wavelets, which spread out to form the next wave front

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21
Q

How did huygen explain reflection?

A

as the whole wavefront doesnt reach the surface at once, wavelets spread away from the surface once they reach it and rejoin with others to reform the reflected wavefront

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22
Q

How did huygen explain refraction?

A

it was assumed that light travels slower in a dense medium so it would slow down and bend towards the normal

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23
Q

why was newtons theory more believed?

A

newton had a higher reputation and diffraction and the speeds of light had not yet been measured

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24
Q

What happens in young double slit?

A

coherent light is shone through 2 slits so that it diffracts. each slit acts as a coherent point source making a pattern of light and dark fringes

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25
Q

what would happen in youngs double slit if newton was right?

A

an interference pattern wouldnt be formed, instead there would only be 2 bright fringes corresponding to the 2 slits

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26
Q

what caused huygen to be believed?

A

the speed of light was measured in water and found to be slower which contradicted newtons theory

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27
Q

How are electromagnetic waves formed?

A

They are formed by alternating magnetic and electric fields travelling in phase at right angles

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28
Q

what is the difference between permitivity and permeability?

A

permitivity relates to the electric field stength to the charge on the object, which formed in the field. Permeability relates to the magnetic flux density produced by a wire to the current in the wire

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29
Q

what did Hertz discover and how?

A

he discovered radio waves by using apparatus which allowed high voltage sparks to jump across a gap of air as this leads to the production of radio waves

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30
Q

How could the radio waves be detected? (2)

A

Dipole reciever - detects the waves’ electric field. Made by placing a second set of charged plates parralell to those forming the high voltage sparks
A loop of wire with a gap - detects the waves’ aleternating magnetic field as the field will enter the loop causing a change in magnetic flux, inducing a potensial difference which will cause a spark to cross the gap in the wire

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31
Q

What happens when a metal sheet is placed infront of the Hertz apparatus?

A

the radio waves are reflected back on themselves causing stationary waves. This meant that frequency could be found and used to calculate speed

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32
Q

What was significant about the speed of the radio waves that hertz found

A

It matched maxwell’s predicted value of the speed of electromagnetic waves, which confirmed that radiowaves were EM waves

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33
Q

what did Maxwell predict?

A

he predicted that EM waves existed and theorised a formula for thier speed

34
Q

what was found about the radio waves hertz produced?

A

they were polarised

35
Q

what method did Fizeau use to determine the speed of light? (3)

A

1) a pulsed beam of light is passed through a gap in a (slow rotating) toothed wheel and reflects on a mirror a large distance away causing it to return backthrough the same gap
2) the rotation speed is increased until the light beam can no longer be seen because it is blocked by a tooth in the wheel next to the gap it could previously go through
3)using the frequency of the wheel and the number of teeth the speed of light could be calculated

36
Q

What was significat about the speed of light fizeua found?

A

It was close to maxwells prediction, providing evidence that light could be an EM wave

37
Q

what calculation can be used to caluclate speed of light in fizeaus experiment?

A

4dnf

distance (d), number of teeth (n), frequency of revolution (f)

38
Q

what does a black body do?

A

emits and absorbs all possible wavelengths of radioation

39
Q

What happened in the ultraviolet catastrophe?

A

wave theory predicted that as the wavelength of radiation decreases, the intensity of the radiation would increase, leading to a prediction of of infinite amount of ultraviolet radiation being emmited. This was not supported by experimental evidence

40
Q

How was the ultraviolet catastrophe solved?

A

By using plancks interpretation of EM waves where he says that EM waves travel in discrete packets called quanta where their energy is directly proportional to their frequency

41
Q

Why couldnt the phototelectric affect be explained by wave theory? (4)

A
  • couldnt explain threshold frequency because it suggested that any frequency of light should work
  • the photoelectric affects is immediate but it suggested that would take time to reach work function
  • increasing intensity didnt increase the speed of emmision
  • photoelectrons are relased with a range of kinetic energies
42
Q

how did einstein expand on planks work?

A

he talked about light being released as photons

  • when a photon interacts with an electron, all of its energy is transferred to it and a electron can only interract with a single proton. threshold frequency is the frequency at which the photon energy is equal to work function
  • the photon energy is tranferred immediately
  • intesity increases number of electron relased per seconds
  • all electrons will recieve same amout of energy but some are deeper in the metal and will lose energy through collisions
43
Q

what does the de broglie hypothesis state

A

all particles have a wave-like nature and particle nature

44
Q

what provided evidence for de broglie hypothesis?

A

electron diffraction. it showed that electrons, which are particles, can also undergo diffraction, which can only be experienced by waves

45
Q

how did de broglie perform his diffraction experiment?

A

1)an electron gun accelerated electrons through a vaccum tube towards a crystal lattice, where they interacted with the small gaps between atoms and formed a diffraction pattern on a flurescent screen behind the crystal

46
Q

how did de broglie perform his diffraction experiment?

A

1)an electron gun accelerated electrons through a vaccum tube towards a crystal lattice, where they interacted with the small gaps between atoms and formed a diffraction pattern on a flurescent screen behind the crystal

47
Q

what is the equation specific to the crystal lattice experiment?

A

λ = h / √meV

Planck’s constant (h), Charge of Electron (e), mass (m), Accelerating voltage (V)

48
Q

What is the resolving power of a microscope?

A

Its ability to distinguish structures which are close to each other

49
Q

Why do electron microscopes have a much higher resolving power than light microscopes?

A

The wavelength of an electron beam is much smaller then that of light. As the wavelength of the electrons decrease, the resolving power of the microscope increases

50
Q

What are the 2 types of electron microscope?

A
  • Transmission electron microscope (TEM)
  • Scanning tunnelling microscope (STM)
51
Q

What happens in a transmission electron microscope?

A

electrons are accelerated by an electron gun, and pass through a set of magnetic lenses all of which have different purposes, passing through an extremely thin sample so that the electrons do not slow down, and thier wavelength doesnt change.

52
Q

What do all the lenses have in common?

A

The will all leave electrons at the centre of the lens undeflected, but will deflect electrons at the edge of the lens towards the axis (centre of the microscope)

53
Q

What are the 3 lenses and what do they do?

A
  • Condenser lens - 1st lens, deflects the electrons so they form a wide parallel beam directed at the sample
  • Objective lens - 2nd lens, forms and image of the sample, which is directly above it
  • Projector lens - 3rd lens, magnify the image made by the objective lens and project it onto the florescent screen
54
Q

What happens in a TEM when the accelerating voltage of the electron gun is increased?

A

the speed of the electrons will increase so thier wavelength will increase causing thier resolving power to increase

55
Q

what is the resolving power of a TEM microscope limited by? (2)

A
  • sample thickness
  • electrons travelling at a range of speeds could cause image to become blurry
56
Q

What happens in a scanning tunnelling microscope?

A

An STM uses a quantum tunnelling of electrons in order to form an image of the surface of an object. Quantum tenneling occurs due to the wave nature of electrons, meaning that if the barrier they are trying to cross is samll enough, electrons can move across just like waves would be able to. smaller gap/barrier = more likely tunnelling will occur

57
Q

what is a scanning tunnelling microscope made of?

A

An STM is formed of a very fine tipped probe, which moves across the surface of an object and stays at a constant potensial (negative or positive), meaning electrons can only travel in one direction. This movement is the tunneling current. As the probe moves the size of the gap will vary. when it becomes larger, tunnelling current decreases as tunnelling is less likely to occur and vice versa

58
Q

what are the 2 ways a STM can operate?

A
  • constant height mode - the probe is kept at constant height mode as it moves across the surface and the tunnelling currnet is recorded and used to creat an image of the surface of the object
  • constant current mode - the current is constantly monitored and fed back to the microscope allowing it to adjust the probes height so the current is kept constant
59
Q

what is absolute motion?

A

The idea that everything moves relative to the ether, which scientists originally believed was a substance which permeated the entire universe

60
Q

how did Michelson and morley investigate the absolute speed of the earth through the ether?

A

they used apparatus known as the interferometer which was formed of a partially reflective surface (beam splitter), a glass block (compensating plate) and two mirrors. The partially reflective surface would reflect some light while allowing some to pass through, creating 2 beams of light moving perpendicular to each other, which travel towards the 2 mirrors which are set up the same distance from the beam splitter. The galss block is used to make sure the 2 beams of light pass trhough the same amount of glass. After being reflected on the mirrors, the 2 beams of light return to a detector and the interference pattern they form can be recorded

61
Q

How did Michelson and Morely get it wrong?

A

they believed that the speed of light travelling parralel to the motion of the earth would be affected, while the speed of light perpendicular wouldnt. They believed the light moving parralell would take longer to travel, therefore rotating the apparatus 90 degrees would cause a shift in the interference pattern. However the interference pattern didnt change, showing that time taken to travel was unafected by the rotation

62
Q

What 3 conclusions came from the Michelson and Morely experiment?

A
  • The ether didnt exist or the earth drags it along when it moves
  • The speed of light in invarient in free space, meaning the speed of light is independent of the motion of the source or the observer
63
Q

What are inertial frames of reference?

A

Frames that move at constant velocity relative to each other, therfor a fram of that is accelerating or rotating cannot be an inertial frame of reference

64
Q

What are the postulates that Einsteins theory of special relativity is based on?

A
  • the speed of light is invarient
  • The laws of physics have th esame from in all inertial reference frames
65
Q

What is time dialation?

A

A consequence of special relativity, meaning it only occurs in inertial frames and causes time to run at different speeds depending on the motion of an observer

66
Q

What do all the symbols mean in the first relativity equation for time dilation?

A

proper time / time passed by observer at event (stationary observer) (t_0) , time passed by external observer (t) , velocity that stationary observer moving at (v) , speed of light (c)

67
Q

Mhy does muon decay provide experimental evidence for time dialation?

A

Muons enter the atmosphere at very high speeds and so experience significant time dialation, which affect how quickly they decay

68
Q

How do you measure muon time dialation?

A

You must place one detector at high altitude and one much further down to measure the change in muon count rate, you also need to measure distance between dtectors and the speed of the muons

69
Q

What is Length contraction?

A

A consequence of special relativity, it only occurs in inertial refernce frames and causes the length of objects moving at high speeds to appear shorter to an external observer

70
Q

What do all the symbols mean in the second relativity equation for length contraction

A

proper length / length measured by person at the event (stationary observer) (l_0), length measured by external observer (l)

71
Q

Is width affected by length contraction?

A

No, only length

72
Q

What happens to mass during energy transfer?

A

Transferring energy to an object will cause its mass to increase, while transferring energy away
from an object will cause its mass to decrease. The faster the object, the more massive it becomes

73
Q

What do all the symbols mean in the third relativity equation for mass change?

A

proper mass / mass measured by person at the event (stationary observer) (m_0), mass measured by external observer / relativistic mass (m)

74
Q

Which of the relativity equations is the mass one the same as?

A

time dialation

75
Q

What did Bertozzi’s experiment include and what does it provide?

A

It provides experimental evidence for the increase in mass of an object with speed. It involved a particle accelerator which could emit electrons at varying kinetic energies, 2 detectors connected to an oscilloscope and an alluminium plate connected to a temperature sensor

76
Q

What happened in Bertozzi’s experiment?

A

Electrons were released in pulses and the time taken to travel between the detectors could be calculated by measing the distance between the peaks and troughs on the oscillioscope. Next, the distance is measured and the speed of the electrons is calculated. The electrons are directed at the aluminium target and when they collide with it, their kinetic energy is transferred to the target in the form of heat. The canhe in temperature is measures, meaning the kinetic energy of the electrons could be directly measured

77
Q

What did Bertozzi find?

A

That his values were very close to einsteins theory of special relativity, meaning his experiment was evidence to prove it

78
Q

Why can an object never reach the speed of light?

A

As an object approaches the speed of light, its mass approaches infinity and so its energy also approaches infinity, which is impossible beacuase you cant have infinite energy

79
Q

What er the fundamental units? (6)

A

Mass, length, time, amount of substance, temperature, current

80
Q

What are the 2 errors?

A
  • Random - affect precision, cant get rid of all of them, make a mean
  • Systematic errors - affect accuracy, affect machinery, calibrate stuff
81
Q

How do you combine uncertainties?

A
  • add/subtract - add uncertainty
  • timsing/dividing - times uncertainty

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