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Physics > P3 topic 4 > Flashcards

P3 topic 4 Flashcards

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1
Q

principle of conservation of momentum

A

for a system of colliding objects, where there are no external forces, the total momentum before and after the collision remains the same

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2
Q

what are the two types of collisions?

A

elastic and inelastic

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3
Q

elastic collision

A

total momentum is conserved, total energy is conserved, KE is conserved

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4
Q

inelastic collisions

A

total momentum is conserved, total energy is conserved, KE isn’t conserved- it’s transferred to other forms such as heat and sound

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5
Q

example of an inelastic collision

A

when a ball bounces on the ground, it doesn’t regain its original height

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6
Q

what factors may affect the rebound height of a ball?

A

material of the ball, type of surface and the initial height

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7
Q

what will happen in a totally inelastic collision?

A

the 2 objects will stick together and move off as one object with a common velocity

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8
Q

what does ordinary matter consist of?

A

neutrons, protons and electrons

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9
Q

what is different about particles of antimatter?

A

they have the opposite change of the particles of matter

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10
Q

positron

A

had an identical mass to an electron, but has an equal and opposite charge

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11
Q

anti-proton

A

has the same mass as a proton, but equal and opposite charge

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12
Q

annihilation

A

when a positron and electron collide they destroy each other completely

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13
Q

what is conserved in annihilation?

A

total mass of both particles is covertly into energy in the form of gamma rays- mass-energy is conserved; there are 2 gamma rays which fly off in opposite directions so that momentum is conserved

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14
Q

what also remains constant during annihilation?

A

total charge remains constant- gamma rays are EM radiation and have no charge

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15
Q

how do PET scanners work?

A

patient is placed in a ring of gamma ray detectors which are connected to computers; positrons emitted by tracers collide with electrons to produce 2 gamma ray pulses in opp directions; diff in arrival times and location of detection of 2 gamma rays is analysed by the computer to work out exact location of annihilation and hence radioactive tracer can be pinpointed; computer builds up a 3D image of distribution of tracer in body

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16
Q

what are PET scanners used for?

A

to study cancer, Alzheimer’s disease, dyslexia and epilepsy

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17
Q

mass energy equation

A

E= m c2

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18
Q

what is happening to an object moving in a circle at a constant speed?

A

it’s continuously changing its direction of motion- it’s velocity is constantly changing and therefore it’s accelerating

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19
Q

centripetal force

A

the resultant force acting at right angles to the velocity of an object that gives rise to circular motion- always directed towards the centre of a circle

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20
Q

what must happen for an object to be moving in a circle?

A

a centripetal force must be acting on it

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21
Q

what type of quantity is momentum?

A

a vector quantity, as it has both direction and magnitude

22
Q

what will a charged particle moving within a magnesium field experience?

A

a force which is always at right angles to its velocity- a centripetal force

23
Q

what will this centripetal force do?

A

make the charged particle go around in a circular path

24
Q

what will happen to the radius in a given magnetic field?

A

the radius will increase as the speed of the particle increases

25
Q

what will happen to negative and positive charges in a magnetic field?

A

they will move in opposite directions

26
Q

what does a cyclotron do?

A

it uses a magnetic field to accelerate charged particles in a circular path

27
Q

how does a cyclotron work?

A

it has 2 hollow D-shaped metal cavities called dees which are enclosed in an evacuated chamber; powerful electromagnets are used to provide a uniform magnetic fuel at right angles go the plane of the dees; a source of particles is placed at the centre of the cyclotron; the dees are connected to a very high frequency alternating voltage supply which repeatedly reverses the polarity of the dees

28
Q

what happens if the source at the centre of the cyclotron produces positively charged protons?

A

if dee A is negative, the protons will be accelerated across the gap and travel in a semicircle in dee A; when protons arrive at gap again, charges on the dee are reversed so protons are accelerated towards dee B; their speed has increased so they now travel in a larger diameter circular path in dee B; process is repeated many times before the proton exits at a very high speed

29
Q

what are cyclotrons used to produce?

A

radioactive isotopes which have been accelerated in cyclotrons

30
Q

how can fluorine-18 be produced?

A

if oxygen-18 in enriched water is bombarded with protons

31
Q

what’s also produced in the reaction to create fluorine-18?

A

a neutron which isn’t harmful and dangerous high-energy gamma rays

32
Q

where does the cyclotron need to be situated in relation the the hospital?

A

many of the isotopes produced in cyclotrons have short half-lives, so the cyclotron needs to be close to the site of the PET scanner

33
Q

what do particle physicists believe all matter to be made up of?

A

2 fundamental groups of particles- quarks and leptons

34
Q

what are made up of quarks?

A

neutrons and protons

35
Q

what are examples of leptons?

A

electrons and neutrinos

36
Q

what do physicists study to investigate the structure and behaviour of particles?

A

the collisions between high-speed electrons, protons and ions with matter

37
Q

what do particle accelerators do?

A

they use electric and/or magnetic fields to accelerate charged particles almost up to the speed of light

38
Q

linear accelerators

A

they are long and straight- the longest one is over 3km long

39
Q

what shape are some accelerators?

A

circular- so that the charged lady led accelerate around several times to increase their velocity

40
Q

small circular accelerators

A

cyclotrons

41
Q

CERN

A

The European Organisation for Nuclear Research

42
Q

what do CERN do?

A

it’s an international organisation whose main purpose is to provide particle accelerators for high energy particle physics research

43
Q

what do CERN’s facilities include?

A

the world’a largest accelerator- the Large Hadron Collider (LHC) and are located on the French-Swiss border

44
Q

LHC

A

most expensive particle accelerator in the world; collides protons and ions at higher speeds and energies than have ever been possible before; accelerates particles in a circular path; uses superconducting electromagnets at very low temperatures to produce strong magnetic fields which are used to accelerate the particles

45
Q

what is the LHC budget?

A

about €8 billion

46
Q

what is the circumference of the circular path the particles in the LHC are accelerated in?

A

27km and up to 11000 revolutions per second

47
Q

what is hoped about the LHC?

A

work completed with it will help to answer some of the fundamental quest old about the structure of matter, about events just after the Big Bang and also explain why particles have mass

48
Q

what is special about CERN?

A

it’s a pure research organisation and the work it completes may never have any commercial value

49
Q

what does CERN’s constitution state?

A

it must not do with for military purposes and the results of all its experimental and theoretical work must be published and made available to the general public

50
Q

what is CERN an example of?

A

collaborative international research

51
Q

advantages of collaborative international research

A

sharing the cost between many countries and organisations as funni costs are too high for any one organisation; no political barriers to communicating new understanding about the physical world; speeding up progress by sharing ideas among many scientists

Physics (15 decks)

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