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Physics > MODERN PHYSICS > Flashcards

MODERN PHYSICS Flashcards

1
Q

thermionic emission

A

the emission of electrons from the surface of a hot metal

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2
Q

The Photoelectric effect

A

the emission of electrons from a metal, caused by the incidence of electromagnetic radiation of suitable frequency

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3
Q

the threshold frequency

A

the threshold frequency of a metal is the minimum frequency of electromagnetic radiation which will cause photoemission from that metal

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4
Q

pair production

A

creation of a subatomic particle and its antiparticle from another form of energy

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5
Q

pair annihilation

A

the transformation of a particle and its anti-particle into 2 photons of electromagnetic energy

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6
Q

the electron volt

A

the amount of energy gained or lost by a single electron when it moves through a potential difference of 1 volt

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7
Q

radioactivity

A

the emission of either particles or electromagnetic radiation from the nucleus of an atom

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8
Q

X-rays

A

high energy electromagnetic radiation

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9
Q

the law of radioactive decay

A

states that the number of disintegrations per second is proportional to the number of nuclei present
activity = λN

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10
Q

the half-life

A

the half-life of an element is the time taken for half of the nuclei in any given sample to decay.
OR
the half-life of an element is the time taken for the activity of any given sample to decrease to half its original value

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11
Q

one becquerel

A

defined as the disintegration of one nucleus per second

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12
Q

nuclear fission

A

the breaking up of a large nucleus into two smaller nuclei of similar size with the release of energy

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13
Q

nuclear fusion

A

occurs when two small atomic nuclei join together to form a larger nucleus, accompanied by the release of large amounts of energy

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14
Q

properties of a cathode ray

A
  • consist of electrons travelling at high speed
  • they travel in straight lines from the cathode to the anode.
  • they cause certain substances to fluoresce when struck.
  • they have kinetic energy
  • they can be deflected by electric and magnetic fields
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15
Q

properties of X-rays

A
  • they are electromagnetic radiation, of very high energy.
  • they pass through many materials, such as skin and muscle tissue.
  • they will not pass through more dense material (bone).
  • they affect photographic film
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16
Q

atomic number

A

the number of protons in the nucleus

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17
Q

mass number

A

tells us the total number of protons and neutrons in the nucleus.

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18
Q

isotopes

A

atoms of the same element which have different numbers of neutrons and therefore different mass numbers

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19
Q

α- particles

A

these are the nucleus of a helium atom (2 protons and 2 electrons). They are relatively big, and have a positive charge. They have very good ionizing ability, but poor penetrating ability (a few cm in air).
The emission of α-particles reduces the atomic number by 2, and the mass number by 4.

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20
Q

β-particles

A

these are electrons. They are formed when a neutron divides into the nucleus to become a proton and an electron. They have good ionizing ability and reasonably good penetrating power (30-40cm in air, a few mm of aluminium).
The emission of β-particles increases the atomic number by 1.

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21
Q

γ-rays

A

this is high energy electromagnetic radiation. it is released because the protons and neutrons rearrange themselves inside the nucleus. It is poor at ionizing, but has a very good penetrating power (few cm of lead).
The emission of γ-rays has no effect on the mass and atomic numbers.

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22
Q

Robert Milikan is usually associated with what physical quantity?

A

the charge on an electron

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23
Q

properties of an electron

A 
negative charge
negligible mass
orbits nucleus
no internal structure
deflected by electric / magnetic field
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24
Q

irishman who gave the electron its name in the 19th century

A

George Stoney

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25
Q

ways of deflecting a beam of electrons

A

by means of an electric field and magnetic field

26
Q

how are electrons accelerated in a cathode ray tube

A

by the high positive voltage at the anode

27
Q

what happens to the energy of the electron when it hits the screen of the CRT

A

it gets converted to light

28
Q

applications of the photoelectric effect

A

sound track in film
photography
burglar alarm

29
Q

photon

A

a packet of electromagnetic radiation

30
Q

why was the quantum theory of light revolutionary

A

light has a particle nature as well as a wave nature

31
Q

explain why the leaves of the golf leaf electroscope collapse when zinc metal is placed near it

A

photoelectric emission occurs (emissions get emitted from the surface of the metal)
the leaves become uncharged and therefore collapse

32
Q

explain what is meant by “zinc has a threshold frequency of 1.04 x 10^15 Hz”

A

below this frequency electromagnetic radiation / photons will not cause emission of electrons (from the zinc).

33
Q

what property of light controls the photocell

A

intensity

34
Q

how do xrays differ from light rays

A

xrays penetrate matter / cause ionization, light rays dont

35
Q

who discovered xrays

A

Wilhelm Rontgen in 1895

36
Q

how are xrays produced

A

accelerated electrons strike a metal target causing electrons in the target to rise to a high orbital level. When these electrons fall back down to a lower level they emit the energy as xrays

37
Q

justify the statement “xray production may be considered as the inverse of the photoelectric effect”

A

xray: electrons in, electromagnetic radiation is emitted.
photoelectric: electromagnetic radiation in and electrons are emitted

38
Q

rutherford had bombarded gold foil with alpha-particles, what conclusion did he form about the structure of the atom?

A

the atom was mostly empty space with a dense, positively-charged core and with negatively-charged electrons in orbit around it

39
Q

describe how an emission line spectrum is produced

A

when the gas is heated the electrons in the gas move up to a higher orbital level and as they fall back down, they emit electromagnetic radiation of a specific frequency

40
Q

examples of radioisotopes

A

iodine
caesium
radon
carbon 14

41
Q

what is measured by the becquerel

A

rate of decay

activity of a radioactive substance

42
Q

uses of radioactive isotopes

A 
battery of heart pacemakers.
irradiation of food
killing cancer cells 
measuring thickness
smoke detectors
43
Q

instrument used to detect radiation / alpha particles / measure the activity of a sample

A

geiger muller tube

44
Q

principle of geiger muller tube

A

incoming radiation causes ionisation of the gas

45
Q

what is ionsiation

A

occurs when a neutral atom loses or gains an electron

46
Q

material in which fission occurs

A

uranium

plutonium

47
Q

parts of a nuclear fission reactor

A

fuel rods, control rods, shielding, moderator, coolant

48
Q

what is the function of the moderator in a fission reactor

A

to slow down fast neutrons to facilitate fission

e.g. graphite / heavy water

49
Q

role of neutrons in nuclear reactor

A

to cause nuclear fission / to initiate reaction

50
Q

in a nuclear reactor how can fission be controlled or stopped

A

dropping the control rods absorbs the neutrons and prevents further fission

51
Q

type of material control rods are made of

A

boron, steel, silver

52
Q

explain how the heat exchanger operates

A

energy from reactor transfers to liquid in heat exchanger to drive a turbine

53
Q

why is it necessary to use a heat exchanger

A

the material in the reactor is radioactive / allows the core to reach a higher temperature

54
Q

positive and negative environmental impacts of fission reactors

A

positive - no CO2 emissions / no greenhouse gases / no gases to result in acid rain
negative - radioactive waste / potential for major accidents

55
Q

application of fission

A

generating electrical energy

bombs

56
Q

source of the suns energy

A

nuclear fusion

57
Q

why are large temperatures required for fusion to occur

A

nuclei are positively charged so enormous energy is required to overcome the very large repulsion

58
Q

advantages of fusion over fission

A

hydrogen fuel from the sea is plentiful - uranium for fission is scarce.
no radioactive waste with fusion - fission results in radioactive waste

59
Q

Work function

A

Φ the minimum energy needed to remove the loosest electron from the surface of that material

60
Q

Isotopes

A

Atoms of an element that have the same number of protons but different numbers of neutrons

61
Q

Activity (A)

A

The activity of a radioactive substance is the number of nucleus of that substance decaying per second

62
Q

The mole

A

A mole of any substance is the amount of that substance that contains as many particles as there are atoms in exactly 12grams 12
6 C.
This number is 6.02x10^23 and is called Avogadro number

Physics (6 decks)

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