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Physics H > Unit 1 > Flashcards

Unit 1 Flashcards

1
Q

What is an field?

A

A region of space where an object will experience a force without being touched

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2
Q

Where do electric fields exist?

A

Around charged particles and between parallel charged plates

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3
Q

In what direction do electric fields always point?

A

Positive to negative

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4
Q

For electric fields between parallel plates, field lines must:

A

Point from + to -

Be parallel and at right angles to the plates

Be equally spaced

Touch the plates

End bits usually ignored

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5
Q

How do electric fields work?

A

Each particle experiences an unbalanced force due to the electric field and so it will accelerate

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6
Q

What is the same as work energy?

A

Kinetic energy

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7
Q

What is potential difference?

A

The work energy gained by 1C of charge (due to an electric field)

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8
Q

What produces a magnetic field?

A

Moving charges or a flow of charges

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9
Q

What experiences a force in a magnetic field?

A

Moving charged particles

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10
Q

Right hand rule

A

For electrons

thumb-thrust
index-field
middle-electron flow (original)

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11
Q

Three main parts of particle accelerators

A

Electric fields-used to accelerate the particles across a potential difference (work done=QV=gain in kinetic energy)

Magnetic fields-used to change the direction of (or deflect) the charged particles

Collision chambers and detectors-where high energy collisions of charged particles take place to produce other particles which can be studied

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12
Q

Three types of particle accelerators

A

Linear accelerators

Cyclotron

Synchrotron

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13
Q

what is not needed in a Linear Accelerator?

A

No magnetic field needed as particles are accelerated in a straight line across more than one voltage

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14
Q

Linear accelerator- Why is it important that an ac supply is used?

A

To keep the particles accelerating in the correct direction. This is done by keeping the electric fields in the correct direction

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15
Q

Linear accelerators- Why do the ‘drift tubes’ get longer?

A

Because the particles keep getting faster so they can travel further in the same time. The time is the same to ensure they stay in sync with the alternating supply.

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16
Q

Cyclotrons-what fields?

A

Use both magnetic and electric fields to accelerate particles

When it reaches the outer edge of the cyclotron the particle beam is extracted and used in other experiments such as collisions

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17
Q

Cyclotron - why is an ac power supply used?

A

as the direction the particle enters the accelerating gap changes, the electric field also needs to change so it is always pointing in the correct direction to accelerate the particle

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18
Q

How do synchrotrons work?

A

They use a magnetic field which gets stronger as the particles get faster, allowing the radius of the path to stay constant

They have accelerating cavities at many different points around the ring to increase the speed of the particles they go around

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19
Q

What are the two main groups of fundamental particles?

A

Fermions
Bosons

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20
Q

What are Fermions?

A

Particles of matter
Eg quarks and leptons (fundamental particles)
(hadrons)

quarks-up, down, strange, charm, top, bottom

leptons-electron, muon and tau, together with their neutrinos

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21
Q

How was the existence of quarks proved?

A

By high-energy collisions between electrons and nucleons (neutrons and protons) in particle accelerators

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22
Q

What are bosons?

A

Force exchange particles

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23
Q

examples of bosons

A

Photon-carrier of electromagnetic force
Gluon-carrier of strong nuclear force
W boson-carrier of the weak nuclear force (can have - or + charge: antiparticles of each other)
Z boson-carrier of the weak nuclear force (has no charge - is its own particle)

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24
Q

What are Hadrons?

A

composite particles made of quarks?

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25
Q

Examples of hadrons

A

Baryon-3 quarks or 3 antiquarks

Mesons-made of a quark and antiquark

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26
Q

Anti matter

A

Each particle in the standard model has a corresponding anti-particle

Identical in every way apart from electric charge

Bar above symbol

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27
Q

How do we know anti particles exist?

A

When a particle and its antiparticle meet they perfectly annihilate each other

Their combined mass is converted into energy

The energy produced from the annihilation is our evidence for the existence of antimatter

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28
Q

What was the first evidence for the neutrino?

A

Beta decay

when a nucleus decays in beta minus decay, an anti-electron neutrino is also given out alongside the electron

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29
Q

1ev=

A

1.6x10^-19J (energy an electron gains when accelerated through 1V

W=QV

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30
Q

Isotopes

A

Atoms of the same element but with a different number of neutrons in the nucleus

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31
Q

examples of elements which can undergo spontaneous fission

A

Plutonium 239
Uranium 235

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32
Q

Radioactive decay

A

An element can decay to become more stable by alpha, beta or gamma emission

33
Q

Induced nuclear fission

A

The splitting of an unstable nucleus from neutron capture into 2 smaller parts (releasing energy and more neutrons)

34
Q

Nuclear fusion

A

Two nuclei joining together to form a larger nucleus (releasing energy and sometimes more particles)

35
Q

Why is energy released in a fusion or fission reaction?

A

Mass is lost and converted into energy

36
Q

What does E=mc^2 represent?

A

Equivalence of mass and energy

mass and energy are interchangeable

In many nuclear reactions, there is a very small decrease in the overall mass of the particles involved

This lost mass is converted into energy

37
Q

Why is containing nuclear fusion challenging?

A

Due to extremely high temperatures required
H2 used (which is now plasma) is too hot to come into contact with any material

38
Q

Solution for containment of nuclear fusion?

A

To contain H2 plasma within toroidal magnetic field. The device that does this is called a tokamak

39
Q

Issues and challenges with fusion reactors

A

Energy-huge amounts of energy need to heat H2 to plasma hot enough to undergo fusion

Containment-very large magnetic fields needed to keep the plasma (full of charged particles) inside the tokamak

Cooling-Fusion produces very hot neutrons which are not contained by the magnetic field. These heat up the walls of the reactor which will need to be cooled. This is where the extracted energy comes from

40
Q

What is irradiance?

A

The irradiance of a source of radiation is the power (energy per second) incident on a unit area of surface (1m^2)

41
Q

sphere area

A

4pir^2

42
Q

What is irradiance directly and indirectly proportional to?

A

directly- 1/d^2
indirectly- d^2

43
Q

charging the gold leaf electroscope

A

charging by induction-electroscope is charged oppositely to charge rod

bring rod->touch->take finger away->take rod away

don’t let rod touch

44
Q

Conclusions of gold leaf electroscope practical

A

only uv light has an effect

only negatively charged electroscopes can be discharged

the effect is only apparent in some metals

45
Q

explanation of the photo-electric effect

A

energy needs to be passed onto an electron to make it escape. Light is regarded as a stream of ‘particles’ called photons. Which carry ‘packets’ of energy depending on the frequency of the light

each electron can absorb a single photon

If a photon has a high enough energy, an electron is freed. If not, then it won’t be freed

46
Q

What is the photoelectric effect evidence for?

A

The particle model of light. This shows that each photon contains a fixed (discrete) amount of energy. Each individual photon will remove one electron.

47
Q

E=hf

A

frequency
planck’s constant-6.63x10^-34J
energy of photon

each photon will have an energy dependent on its frequency

48
Q

What is the work function

A

E^o

Each electron has a minimum energy to ‘just’ free it.

This means that each photon must have a minimum energy and minimum frequency associated with it, called the threshold frequency

E^o = hf^o

49
Q

What if a photon energy e=hf where f>f^o?

A

Then E^o of that energy frees it and the rest gives the e electron kinetic energy

50
Q

Ek=hf-hfo

A

kinetic energy of electron
photon energy
work function (of electron)

51
Q

What effect does increasing the irradiance of a light source have on the maximum kinetic energy gained by the electrons when they leave the surface of the metal

A

no effect

52
Q

When are two waves coherent?

A

If they they are produced by the same source.

They will have the exact same frequency,wavelength, velocity, and they have a constant phase relationship

53
Q

Constructive interference

A

If 2 coherent waves meet completely in phase with each other

Amplitude gets louder

Peak to peak
trough to trough

54
Q

Destructive interference

A

If 2 coherent waves meet completely out of phase with each other by half a wavelength

Amplitude is zero

peak to trough

55
Q

What is interference?

A

When 2 waves combine to make a resultant wave. This wave can have a smaller, larger or same amplitude as original waves

56
Q

Path difference

A

Difference in distance to one point by 2 waves

If equal to a whole number of wavelengths—>waves will meet in phase and interfere constructively

If equal to odd number of half wavelengths—>waves will meet completely out of phase and interferendestructively

57
Q

how to find d in dsinx

A

d is difference between gratings

you need to divide 1mm by the number of lines per mm to find ‘d’

58
Q

Prism v grating patterns (white light)

A

Prism
-spectrum produced by refraction
-a single spectrum produced
-short wavelengths refract most

Grating
-spectrum produced by interference
-central white fringe
-spectra occur in pairs either side of central fringe
-long wavelengths in the outer edge

59
Q

Bohr model of the atom

A

Neil Bohr proposed that

1-the nucleus contains protons and neutrons and is positively charged
2-electrons orbit the nucleus in discrete energy levels

energy levels are of an exact value-electrons can only be in one of these allowed energy levels

60
Q

Absorption spectrum

A

produced by the gases in the sun’s atmosphere

provides evidence for the elements that exist in the sun’s atmosphere

Black lines of colour missing

cool gas absorbs the same lines of light

61
Q

Emission line spectrum

A

Lines of colour on black

hot gas emits lines of light

The coloured lines correspond to the colour of wavelength (wavelength of photon) that an excited electron emits as it falls to a lower energy level.

Different transitions produce different lines/frequency of photon

62
Q

What is the ionisation level?

A

The level where the electrons have 0 potential energy due to the nucleus

63
Q

What does it mean if a line in an emission line spectrum is brighter than the others?

A

More photons of that frequency/wavelength are given off

This means more electron transitions must have taken place between those energy levels and are more common

64
Q

what is sinxair directly proportional to?

A

sinxperspex

65
Q

What is the refractive index?

A

It is defined as the ratio of the speed of light in a vacuum to the speed of light in the medium (n)

66
Q

What happens to the refractive index of a medium when the frequency of light increases?

A

Increases

67
Q

What is the critical angle?

A

The angle of incidence which produces an angle of refraction of exactly 90 degrees (theta c)

68
Q

When does total internal refraction occur?

A

If light meets a boundary at an angle greater than the critical angle total refraction occurs and the light does not refract out of the block.

69
Q

What is a continuous spectrum?

A

consists of all visible wavelengths

produced by sunlight, filament lamps etc (‘white’ light sources)

70
Q

What is a line spectrum?

A

produced by elements (in gas form)

consists of very specific wavelengths of light which are emitted or absorbed by the element

71
Q

How can you increase the spacing between maxima on the interference pattern? Why would you want to do this?

A

increasing wavelength

decreasing d (smaller slits, less distance between slits)

increasing d(distance of grating to screen)

(smaller percentage uncertainty as angles are bigger)

72
Q

How is an line emission spectrum produced?

A

If an electron is in an excited state, it can return to a lower energy level. When it does this, it emits a photon. Different transitions produce different lines/frequencies (of photons)

73
Q

How is a line absorption spectrum produced?

A

When photons of light pass through a gas, the photons with the same energy as the energy gaps in the atoms can be absorbed. This causes an absorption spectra, as shown below.

Because the energy levels are the same, the lines in the emission spectra of an element are in the same position as the lines in the absorption spectra of the same element, as shown below.

74
Q

Evidence for the wave-model of light?

A

double-slit experiment
maxima and minima are produced due to interference

if grains of sand were shot through then they would end up in a line in the same place (same angle)

photoelectric effect
frequency of light determines energy of photons and therefore kinetic energy of emitted electrons

75
Q

Evidence for the particle-model of light?

A

photoelectric effect

76
Q

How to improve irradiance experiment?

A

-smaller lamp will be more like a point source (needs to be a point source to prove inverse square law)

-black cloth on bench to reduce reflections

77
Q

why may a wire have a large diameter?

A

-reduce resistance
-prevent overheating/prevent wires melting

78
Q

What are absorption lines (Fraunhofer lines) in the spectrum of sunlight evidence for?

A

the composition of the Sun’s outer atmosphere

Bohr model of the atom

79
Q

How can you improve the interference grating experiment?

A

-repeat measurements
-use additional gratings
-move screen further away
-use second order maxima to determine angle
-measure angle from first order to first order

Physics H (5 decks)

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