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A-Levels > Physics Paper 2 > Flashcards

Physics Paper 2 Flashcards

1
Q

dielectric

A

between plates in capacitor, an insulating material

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2
Q

capacitors in parallel

A

add

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3
Q

capacitors in series

A

add reciprocals

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4
Q

capacitor uses

A

flash photography, back-up power supplies, smoothing out p.d. (a.c. to d.c.)

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5
Q

same for capacitor discharge and charge equations

A

current

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6
Q

time constant tau

A

time taken for charge, p.d., or current on discharging to fall to 37% (1/e) of original
OR time taken for charge, p.d. to rise to 63% of maximum

note - about 5 time constants to charge/discharge fully

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7
Q

Faraday’s Law

A

induced emf is directly proportional to rate of change of flux linkage

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8
Q

Lenz’s law

A

induced emf always in a direction to oppose the change that caused it

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9
Q

flux linkage

A

N turns x flux

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10
Q

velocity selector

A

only one velocity has balanced electric and magnetic fields (BQv & EQ), rest blocked by collimator

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11
Q

EM practical accuracy

A

Improve accuracy of electromagnetism practical’s by switching off power supply between measurements (heat → resistance → current), and by making sure only length of wire between magnets is perpendicular to field

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12
Q

leptons

A

feel weak nuclear and gravity, not strong nuclear - (electrons, neutrinos)

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13
Q

hadrons

A

feel strong nuclear force - (protons, neutrons, sigmas, mesons)
only protons stable

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14
Q

baryons

A

3 quarks - protons, neutrons

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15
Q

mesons

A

quark and anti-quark

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16
Q

pair production

A
  • Minimum amount of energy required is rest mass energy of both particles
  • usually positron-electron pair due to low mass
  • in annihilation two gamma photons are produced that travel in opposite directions
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17
Q

quark confinement

A

cannot be broken apart from hadrons as mesons produced due to pair production from energy supplied

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18
Q

electric and grav field differences

A
  • Grav always attractive
  • Electric fields can be shielded against
  • Size depends on medium between two bodies for electric
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19
Q

weak nuclear reactions

A
  • beta minus: d -> u + e + antineutrino [neutron to proton]
  • beta plus: u -> d + e+ + neutrino [proton to neutron]
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20
Q

decays and when

A
  • too energetic, too heavy, too many/few neutrons
  • beta minus in neutron rich nuclei
  • gamma in too energetic nuclei
  • alpha in heavy nuclei
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21
Q

moderator

A

slows down neutrons, thermal neutrons, without which fission will slow/stop

22
Q

critical mass

A
  • neutrons escaping proportional to SA
  • as mass increases, smaller fraction escapes, (SA:V decreases)
  • so fraction producing fission increases as mass increases, eventually will hit critical mass where chain reaction occurs
23
Q

binding energy

A
  • mass of a nucleus is less than mass of constituent parts, difference is mass defect
  • The defect is released as energy, and is equal to the energy needed to separate all nucleons, which is binding energy
24
Q

strong nuclear

A
  • repulsive below 0.5fm or would collapse to point
  • 0.5 to 3fm attractive
  • beyond 3fm falls to 0 value, so then cannot hold nucleons together
25
Q

X-ray emission

A

cathode is a heater, thermionic emission releases electrons
- anode is made of tungsten, target metal
- high p.d.
- electrons accelerated to anode, gain KE
- when smash into tungsten, less than 1% of KE converted to X-ray photon
- most converted to heat, so anode will be rotated or something to prevent overheating

26
Q

internal resistance

A

transfers electrical energy to thermal in driving charge through battery

27
Q

coherent

A

same frequency, fixed phase difference

28
Q

filament lamp I-V characteristic

A
  • Ohm’s law obeyed at low p.d.
  • as V increases, I increases, R increases, temp increases
  • stops obeying Ohm’s law, gradient levels out as it is 1/R
29
Q

appropriate distance for microwave standing wave

A

1m between source and reflective plate

30
Q

range of energies of electrons from photoelectric effect

A

all gain same energies from one photon interaction
lose energy in collisions as they travel from deeper within the metal so require more to escape metal

31
Q

radioactive decay constant physical meaning

A

probability of decay per unit time

32
Q

spontaneous meaning (decay)

A

not influenced by external factors such as temperature

33
Q

Kirchhoff’s first law

A

total current entering junction = total leaving

34
Q

Kirchhoff’s second law

A

total emf around series = sum of pd’s across each component

35
Q

X-rays

A

cathode is a heater, thermionic emission releases electrons
- anode is made of tungsten, target metal
- high p.d.
- electrons accelerated to anode, gain KE
- when smash into tungsten, less than 1% of KE converted to X-ray photon
- most converted to heat, so anode will be rotated or something to prevent overheating

36
Q

attenuation (4 types)

A
  • simple scattering
  • photoelectric effect - around 30 keV, absorbed by electron and ejected by atom, gap in shell filled by another electron which releases a photon
  • Compton scattering - 0.5 to 5MeV, knocks electron out of an atom, causing the photon to lose energy and scatter
  • pair production → 1.1MeV, decays into electron and positron
37
Q

contrast media

A

barium sulfate meals - intestine
iodine - blood

38
Q

CAT

A
  • computerised axial tomography
  • emitter on one side of tube, detector on other
  • rotates around patient
  • can be used to generate 3D images
  • more expensive and have to remain still
39
Q

tracers

A
  • usually consist of radioactive isotope bound to substance used by body, water, glucose
  • Technetium-99m used for gamma, 6 hour half-life
  • Fluorine-18 used in PET scans as usually undergoes beta plus decay, 110 minute half-life
40
Q

gamma cameras (5 parts)

A
  • lead shield
  • lead collimator, only gamma rays parallel can pass through
  • sodium iodide crystal - scintillates whenever a gamma ray hits it
  • photomultiplier tubes - detects flashes of light from crystals and turn into pulses
  • electronic circuit - collects signals, sends to computer which processes into image
41
Q

gamma camera price

A

cheaper than PET, and gamma rays are emitted by radiotracers

42
Q

PET

A
  • positron emission tomography
  • radiotracer with short half-life injected with substance used by body (e.g. glucose)
  • positrons emitted collide with electrons in organs, producing gamma rays, which are then detected
  • distribution of radioactivity same as metabolic activity - can be used to detect cancers
  • very expensive, fluorine-18 needs to be produced on site or in specialist lab nearby
  • MENTION ANNIHILATION, 2 OPPOSITE DIRECTIONS, ARRIVAL TIME USED TO FIND POSITIONS
43
Q

ultrasound

A
  • usually about 1-15MHz for medical purposes
  • soft tissues, real-time imaging, no known hazards, cheap and portable, can move during scan, quick (10-15 mins)
  • doesn’t penetrate bone, can’t detect fractures or examine brain, cannot image behind lungs (pass through air spaces), no information on solid masses
44
Q

piezoelectric

A
  • crystals produce p.d. when deformed
  • when a.c. applied to crystal, it vibrates at same frequency
  • can act as ultrasound receiver and transmitter
  • transducers use lead zirconate titanate (PZT) - thickness is half the wavelength
  • ultrasound of this frequency will make crystal resonate, so it is heavily damped to produce short pulses and increase resolution

PZT crystal thickness is half wavelength so reflected waves make crystal resonate

45
Q

bremsstrahlung radiation

A

continuous spectrum, caused by normal X-ray generation mechanism

46
Q

K-lines

A
  • 2nd mechanism is when accelerated electrons collide with inner shell electrons, ejecting them
  • outer shells move in to fill vacancy, release photons of specific X-ray wavelengths (K-lines)
  • or characteristic X-rays, sharp lines on intensity v energy graphs
47
Q

A-scans

A
  • (amplitude), sends short pulse into body while simultaneously having an electron beam sweeping across cathode ray oscilloscope
  • scanner receives reflected ultrasound that appear as vertical deflections on CRO
  • weaker pulses are amplified to prevent information loss (time-gain compensation)
  • horizontal positions indicate time taken for ‘echoes’
    1D
48
Q

B-scan

A
  • amplitude of reflected pulses is displayed as brightness of spot
  • using linear array of transducers, can be 2D
49
Q

emf

A

pd when current is 0

50
Q

electric field lines direction

A

positive to negative

51
Q

electric potential definition

A

work done per unit charge to move a positive charge from infinity to that point

A-Levels (4 decks)

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