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Physics > P2 topic 5 > Flashcards

P2 topic 5 Flashcards

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Physics 101 flashcards AP® Physics flashcards
1
Q

fission reactions

A

take place in a nuclear reactor to generate electricity on a large scale

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2
Q

what happens in a fission reaction?

A

a slow-moving neutron is absorbed by a uranium-235 nucleus, making it unstable; the new nucleus splits into two smaller daughter nuclei and 2 or more fast moving neutrons; energy is released as the kinetic energy of the daughter nuclei and the neutrons

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3
Q

how can fission reactions be triggered?

A

by bombarding uranium-235 nuclei with neutrons

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4
Q

chain reaction

A

a process in which an enormous amount if energy is produced when neutrons from previous fission reactions go on to produce further uncontrolled fission reactions

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5
Q

how do nuclear power stations create energy?

A

most nuclear power stations use uranium or plutonium as fuel for the reactions; a large amount of energy, in the form of KE of the neutrons and the daughter nuclei is released in fission reactions; KE turned into heat and used to boil water to mane steam; steam powers turbines

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6
Q

why is disposal of nuclear waste a major concern?

A

for daughter nuclei produced in fission reactions can remain active for thousands of years

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7
Q

what are the four main components of a reactor?

A

fuel rods, coolant, moderator and control rods

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8
Q

fuel rods

A

contain pellets of nuclear fuel in the form of uranium dioxide

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9
Q

coolant

A

removed the thermal energy produced in the fission reactions in the reactor core, so it can be used to heat water to create steam to power generator turbines (in a water-cooled reactor)

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10
Q

moderator

A

surrounds the nuclear fuel rods and slows down the fast-moving neutrons-slow-moving neutrons have a greater chance of reacting with uranium nuclei than fast-moving neutrons

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11
Q

control rods

A

can be lowered into the reactor to absorb the neutrons and so slow down the fission reactions and control the chain reactions

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12
Q

fusion reactions

A

cause the energy generated by the Sun and the stars

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13
Q

critical mass

A

a chain reaction can only be sustained by a large amount of uranium-235- in small amounts, too many neutrons will escape and not take part in fission reactions; the minimum mass of a fissile material required to sustain a chain reaction

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14
Q

what is the energy released in fission reactions used by?

A

nuclear reactors to produce energy

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15
Q

nuclear fusion

A

a nuclear reaction in which two smaller, lighter nuclei join or fuse together to produce one larger nucleus, creeping vast amounts of energy- the fusing together of hydrogen nuclei to produce helium nuclei

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16
Q

what is needed for nuclear fusion to take place?

A

extremely high temperatures

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17
Q

what is the energy source that keeps our Sun and other stars burning?

A

the fusion of hydrogen and other lighter nuclei

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18
Q

isotopes of hydrogen

A

deuterium and tritium

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19
Q

who were the scientists who claimed to have carried out cold fusion?

A

Stanley Pons and Martin Fleischmann in 1989

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20
Q

cold fusion

A

an invalidated theory that proposed nuclear fusion occurring at room temperature- the scientists claimed that their experiment had produce vast amounts of thermal energy

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21
Q

why were Pons and Fleischmann criticised by other scientists?

A

their announcement gained worldwide publicity- but they had not published enough technical details of their experiment for other scientists to reproduce their results

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22
Q

what do the majority of scientists think about cold fusion?

A

they reject the theory, as it couldn’t be validated by reproducing the experiment

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23
Q

why are fusion reactions more difficult to trigger than fission reactions?

A

hydrogen nuclei (protons) are positively charged and therefore repel one another

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24
Q

how can you improve the changes of a fusion reaction taking place?

A

You can increase the speed at which the nuclei move

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25
Q

what happens at temperatures around 10 million degrees Celsius?

A

hydrogen nuclei move rapidly enough to overcome the electrostatic repulsive forces and join together in fusion reactions

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26
Q

when can nuclear fusion not take place?

A

at low temperatures and pressures

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27
Q

what do you need to do in order to create fusion?

A

hydrogen nuclei must be heated to temperatures of about 100 million degrees Celsius and contained by very strong magnetic fields produced by super cooled electromagnets- it’s Beth difficult to create these conditions on earth

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28
Q

nucleons

A

a term used to refer to either protons or neutrons

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29
Q

ion

A

a charged atom that had lost or gained electrons

30
Q

how can positive ions be created?

A

rubbing insulators together (the friction removes electrons grin the atoms of one insulator) or by heating a gas

31
Q

how does heating a gas create positive ions?

A

thermal energy ionises the gas atoms; electrons of the atoms gain energy and fly off

32
Q

isotopes

A

nuclei of atoms with the same number of protons but a different number of neutrons

33
Q

why do isotopes of an element have the same chemical properties?

A

they all have the same number of electrons

34
Q

radioactive decay

A

some isotopes are unstable- over time, the nucleus breaks up and emits a particle or wave in an attempt to become more stable

35
Q

alpha particles

A

each alpha particle is identical to a helium nucleus, with two protons and two neutrons

36
Q

beta particles

A

each beta particle is an electron emitted from inside the nucleus

37
Q

gamma rays

A

EM waves of very short wavelength

38
Q

ionisation

A

a process in which radiation transfers some or all of its energy to liberate an electron from an atom

39
Q

what does ionisation leave behind?

A

positive ions

40
Q

what is the charge of alpha particles?

A

2+

41
Q

what’s the charge of gamma rays?

A

0

42
Q

what is the typical speed of alpha particles?

A

10 million m/s

43
Q

what is the typical speed of beta particles?

A

100 million m/s

44
Q

what is the typical speed of gamma rays?

A

3 x 10 to the 8 m/s

45
Q

what is the mass of an alpha particle?

A

4

46
Q

what is the mass of a beta particle?

A

0.00055

47
Q

what is the mass of a gamma ray?

A

0

48
Q

how good is the ionising effect of alpha?

A

strong

49
Q

how good is beta at ionising?

A

weak

50
Q

how good is gamma at ionising?

A

very weak

51
Q

what does it take to stop alpha radiation?

A

paper, skin or about 6cm of air

52
Q

what does it take to stop beta radiation?

A

few mm of aluminium

53
Q

what does it take to stop gamma radiation?

A

never completely stopped, but reduced significantly by thick lead or concrete

54
Q

what is the nucleus known as before it decays?

A

the parent

55
Q

what is the nucleus left behind after decay called?

A

the daughter

56
Q

why can’t radioactive decay be predicted or affected by external conditions?

A

it’s random and spontaneous

57
Q

half life

A

the average time it takes for half of the undecayed nuclei in a sample to decay- it can be micro-seconds or thousands of years

58
Q

activity

A

the rate of decay of a source’s nuclei

59
Q

what is activity measured in?

A

becquerel (Bq)- 100 Bq means that 100 nuclei decay per second and that 100 alpha or beta particles are emitted per second

60
Q

what is the relationship between activity and the number of undecayed nuclei in a source?

A

it is directly proportional

61
Q

what is activity inversely proportional to?

A

half-life of an isotope

62
Q

why does the activity of a source decrease over time?

A

as radioactive nuclei decay, there are fewer undecayed nuclei

63
Q

what will a source with a short half life have?

A

a large activity

64
Q

how can radioactive decay be useful?

A

the kinetic energy of the alpha or beta particles emitted from the nuclei can be used to generate electricity on a small scale

65
Q

why is the chain reaction of the uranium nuclei in a nuclear power station controlled?

A

to maintain a steady output of power

66
Q

what does a neutral atom have?

A

the same number of electrons and protons

67
Q

nucleon number

A

mass number

68
Q

proton number

A

atomic number

69
Q

what is ionisation the process of?

A

removing electrons from atoms, leaving behind positive ions

70
Q

what do the numbers decrease by in alpha decay? e

A

proton number decreases by 2 and the mass number decreases by 4

71
Q

is the daughter nuclei of the same element after radioactive decay?

A

no

Physics (15 decks)

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