Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

LC Physics > Modern Physics > Flashcards

Modern Physics Flashcards

1
Q

properties of the electron

A
  • orbits the nucelus
  • very small mass
  • negatively charged
  • smallest amount of charge found in nature
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Who named and who measured the electron?

A
  • named by Irish scientist George Johnstone Stoney

- First measured by American scientist Robert Millikan

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

electronvolt - why use it

A

-the energy of electron is so small, we use a new unit called the electronvolt

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Electronvolt (eV)

A

The electronvolt is the energy gained or lost by an electron when it moves through a potential difference of one volt

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

1 eV

A

1eV = 1.6x10⁻¹⁹ J

on log table

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

thermionic emission

A

giving off of electrons from the surface of a hotel metal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

thermionic emission use

A

can be used to produce a beam of electrons in an evacuated glass tube - cathode ray tube

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

cathode ray tube contents

A

(know diagram)

  • glass tube with a vacuum
  • cathode and anode electrodes
  • screen
  • two sets of parallel plates
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

cathode ray tube procedure

A
  • cathode is heated
  • thermionic emission occurs
  • anode voltage between anode and cathode
  • beam of electrons travel from the anode to the screen, producing a bright spot of light
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

cathode rays

A

streams of high speed electrons moving from the cathode are called cathode rays

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

cathode rays properties

A
  • travel in straight lines
  • cause some substance to give out light
  • have kinetic energy
  • can be deflected in electric and magnetic fields
  • invisible, but can be detected
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

deflection of beam (Electric field)

A
  • if high voltage placed across parallel plates, beam will deflect
  • larger the voltage, more it will deflect
  • if pd is reversed, deflection will go the other way
  • Y-plates control vertical position
  • X-plates control horizontal position
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Deflection of Beam (magnetic field)

A
  • place bar magnet near cathode ray tube
  • beam of electrons will deflect as per Fleming’s left hand rule
  • force is always perpendicular to direction of motion
  • Speed does not change
  • beam of electrons moving at right angles to a magnetic field moves in a circle
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

uses of cathode ray tube

A
  • television
  • computer monitor
  • cathode ray oscilloscope
  • used in Electrocardiogram (ECG)
  • used in Electroencephalogram (EEG)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

When a charge Q moves through a voltage V, the work W done is given by

(not on log tabl

A

W = QV or W = eV

e is charge on an electron, 1.6x10⁻¹⁹ C

Loss in Eₚ = Gain in Eₖ

Gain in Eₚ = Loss in Eₖ

eV = 1/2mv²

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

photoelectric effect

A

the emission of electrons from surface of a metal by electromagnetic radiation of a suitable frequency

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

To show the photoelectric effect

A

know experiment

apparatus: gold leaf electroscope
procedure: shine uv light
result: leaves collapse

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Photocell diagram

A

in notes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Photocell

A

photoelectric cell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

photocell use

A

Used in:

  • solar powered calculators
  • burglar alarms
  • automatic doors
  • control of heaters in central heating
  • sound track in films
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

How photocell works

A
  • conducts electric current when light of suitable freq shines on it. Current proportional to intensity of light
  • Has 2 electrodes (Cathode +, Anode -)
  • Cathode called photocathode, coated in material that will undergo photoemission
  • Anode is rod running up centre
  • tube has a vacuum
  • Photoelectrons emitted when suitable freq light strikes photocathode and are attracted to positive anode
  • Small photocurrent flows while light is on it
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

To demonstrate action of a photocell

A

experiment

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

photocurrent and intensity of light

A

Photocurrent ∝ Intensity of the light

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Threshold frequency

A
  • For a given metal, the freq below which photoemission will not occur is called the threshold frequency
  • Light above this freq will cause photoemission
  • Increased freq does not affect emission
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Threshold freq of diff materials

A
  • Zinc: freq is in UV range

- Alkali metals (group 1): in visible and IR range

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Work function Φ

A

The work function of a metal is the minimum energy needed to remove the loosest electron from the surface of that metal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What must light be considered as?

A
  • Light must be considered as a “packet of energy”

- Each packet is called a photon or quantum of energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Equations

A

E = hf

hf = Φ + 1/2mv² (Einstein's Photoelectric effect)
E = Φ + 1/2mv²

Φ = hf₀

E = energy of the photon!!!!!!!!!!!!!!!
f = freq
h = Planck's constant
Φ = work function
f₀ = threshod freq
1/2mv² = kinetic energy
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Photon

A

A packet of electromagnetic energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

How energy of a photon gotten

A

The energy, E of a photon is given by E=hf, where f is freq and h is Planck’s constant

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

light source and photons

A

the brighter a light source, the more photons it gives out per second

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Einstein’s Photoelectric Law

A

hf = Φ + 1/2mv²ₘₐₓ

Work function = (Planck’s constant)(Threshold frequency)

Φ = hf₀

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

x-rays

A

high frequency electromagnetic radiation produced when high speed electrons in a cathode ray tube strike a metal target that has a high melting point

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

hot cathode x-ray tube

A
  • Thermionic emission at cathode
  • V high voltage across tube (80kV) accelerates electrons towards anode
  • When electrons strike target, some kinetic energy converted to X-rays
  • rest of energy converted to heat, removed by coolant
  • Lead shield to protect operators
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

X-ray is inverse of photoelectric effect

A
  • in photoelectric effect, radiation strikes a metal and electrons emitted from metal
  • in x-rays, electrons strike metal and lose their energy, radiation given off
  • They are opposite to each other
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

properties of x-rays

A
  • electromagnetic waves
  • ionise materials (knock off electrons)
  • penetrate
  • not deflected in electric or magnetic fields
  • fluorescence (glow) in some materials
  • affect photographic emulsions
  • can produce interference patterns
  • can cause photoemission
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

uses of x-rays

A
  • x-ray photographs
  • destroy cancerous cells
  • detect cracks and flaws in metals
  • determine thickness of materials
  • can cause harm to human tissue which may lead to cancers
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

Rutherford’s Experiment

A
  • bombarded gold foil with alpha particles (α-particles) (nuclei of He atoms)
  • caused flashes of light called scintillations
  • Most α-particles undeflected, passed straight through gold foil
  • Some deflected through small angles
  • Some turned back through angles greater than 90 degrees
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

Explanation of Rutherford’s experiment

A
  • Nucleus v small in atom, atom is mostly empty space, so most α-particles passed straight through
  • Deflection occurred if α-particles passed by nuclei as positive will deflect positive
  • If α-particles about to collide head on with nuclei, they turn back
  • Electrons are negatively charged and orbit nucleus
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

Radius of Nucleus

A
  • From number of α-particles deflected, Rutherford estimate radius of nucelus
  • Radius of nucleus in order of 10⁻¹⁵
  • Radius of atom in order of 10⁻¹⁰

Atom is mostly empty space

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

Bohr model

A
  • Danish scientist Niels Bohr proposed model for how electrons orbit the nucleus
  • Evidence for model comes from study of emission spectrum
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

Emission Spectrum

A
  • when light from luminous source undergoes dispersion the resulting pattern is called an emission spectrum
  • Occurs when energy supplied to a material
  • two types: continuous and line spectra
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

continuous spectrum

A
  • Produced by an incandescent (makes light by being heated) solid or liquid
  • all visible wavelengths emitted from red to violet

-can be shown using lightbulb and spectrometer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

incandescent

A

makes light by being heated

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

line spectrum

A
  • produced by a gas which has been given energy
  • colour given off depends on gas being used

-can be shown using gas discharge tube and spectrometer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

excited electrons

A
  • electrons moved only in certain allowed orbits
  • electrons will not give off electromagnetic radiation in some orbits
  • energy level of electron in an orbit is fixed
  • if it is supplied with energy, an electron may become excited and move to higher orbit
  • this energy is quickly lost + it returns to where it was
  • Normal energy called E₁, excited energy called E₂
  • energy given off is difference (E₂ - E₁)
  • energy given off as a photon of electromagnetic radiation of frequency f given by hf = E₂ - E₁
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
47
Q

energy given off as a photon of electromagnetic radiation of frequency f given by

A

hf = E₂ - E₁

h = Planck’s constant

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
48
Q

Laser meaning

A

Light Amplification by Stimulated Emission of Radiation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
49
Q

Lasers

A

Atoms are stimulated by light of same freq to emit photons of energy together making an intense beam of light - laser beam

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
50
Q

Uses of lasers

A
  • Telecommunications
  • Medicine
  • Industry
  • CD players and scanners
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
51
Q

Nucleus

A
  • Made up of positive protons and neutral neutrons
  • Atomic number (Z) = number of protons
  • Mass number (A) = protons plus neutrons
  • Mass number goes on top in Periodic table
  • Isotopes are…
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
52
Q

Isotopes

A

atoms with same number of protons but diff numbers of neutrons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
53
Q

Radioactivity

A

the disintegration or decay of the nuclei of certain atoms with the emission of one or more types of radiation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
54
Q

Who discovered radioactivity

A

Henri Becquerel

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
55
Q

Types of nuclear radiation

A

Alpha radiation α
Beta radiation β
Gamma radiation γ

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
56
Q

Experimental evidence - radiation

A
  • Deflection in electric or magnetic fields (three types deflect at diff angles as they pass thru these fields)
  • Diff types of rad can penetrate thru diff thicknesses
  • Ionisation is the knocking off of electrons, radiation makes materials lose their charge.
  • Can be shown that diff rad types ionise to diff degrees, shown with electroscope
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
57
Q

Ionisation

A

The knocking off of electrons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
58
Q

Radioactive decay

A
  • When alpha or beta particles are emitted.
  • No. of protons changes.
  • That means it becomes a new nucleus
  • Parent nucleus
  • Daughter nucleus (it may also be radioactive)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
59
Q

Parent nucleus

A

The original nucleus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
60
Q

Daughter nucleus

A

The new nucleus (it may also be radioactive

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
61
Q

alpha radiation

A
  • fast moving helium nuclei ejected from nuclei of radioactive atoms
  • A helium nucleus is a bundle of two protons and two neutrons, each bundle called n alpha-particle

-daughter nucleus is two places to left of parent nucleus in periodic table

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
62
Q

Beta radiation

A
  • High speed electrons ejected from nuclei of radioactive atoms
  • Each electron called a beta-particle

-atomic number of daughter nucleus is one greater than that of parent, so it is one place to right on periodic table

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
63
Q

Gamma radiation

A
  • High freq electromagnetic radiation with freqs above those of normal x-rays emitted from nucleus of a radioactive atom
  • Gamma radiation is called gamma radiation

-Nucleus is unchanged, but it loses energy and becomes more stable

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
64
Q

α-particle

Nature, Ionising ability, Penetrating power, Range, Charge, Relative mass, Deflection in fields

A

Nature/structure:
Helium nucleus

Ionising ability:
greatest

Penetrating power:
least

Range:
Few cm air, thin sheet paper

Charge:
+2

Relative mass:
4

Deflected in fields:
As + charged particle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
65
Q

β-particle

Nature, Ionising ability, Penetrating power, Range, Charge, Relative mass, Deflection in fields

A

Nature/structure:
electron

Ionising ability:
Less than alpha

Penetrating power:
More than alpha

Range:
Few mm Al

Charge:
-1

Relative mass:
0

Deflected in fields:
As - charged particle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
66
Q

γ-particle

Nature, Ionising ability, Penetrating power, Range, Charge, Relative mass, Deflection in fields

A

Nature/structure:
Em radiation

Ionising ability:
Least

Penetrating power:
Most

Range:
Many cm of lead, few feet of concrete

Charge:

Relative mass:

Deflected in fields:
undeflected

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
67
Q

Demonstrate penetrating power of alpha, beta, gamma rays

A

experiment

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
68
Q

Demonstrate ionising effect of nuclear radiation

A

experiment

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
69
Q

Activity of radioactive nucleus

A
  • Activity (A) of a radioactive substance is number of nuclei of that substance decaying per sec
  • Unit is becquerel (Bq)
  • 1 becquerel = 1 radioactive disintegration per second
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
70
Q

Radioactive Decay

A
  • Radioactive decay is a random process
  • Law of Radioactive Decay
  • rate of decay proportional to N
  • Rate of decay = λN
  • λ = radioactive decay constant or decay constant, unit is per second
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
71
Q

Law of Radioactive Decay

A

The number of nuclei decaying per second (the activity) is directly proportional to the number of nuclei undecayed

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
72
Q

Half-life

A
  • The half-life T(1/2) of a radioactive isotope is the time taken for half of the undecayed atoms to undergo decay
  • Also time taken for its activity to decrease by half
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
73
Q

Half-life formula (in log table)

A

T₁/₂ = ln 2/λ

or 0.693/λ

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
74
Q

Geiger–Müller tube

A
  • Detects presence of radioactivity by the ionisation it produces
  • Can also measure activity of radioactive sample
  • Radiation passes thru thin mica window into argon gas at low pressure
  • Some argon ionised, producing positive ions and electrons
  • Electrons pick up speed and avalanche of electrons produced
  • Pulse of current flows, which is read on a counter
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
75
Q

Solid State Detector

A
  • Reverse bias p-n junction connected to a counter
  • Radiation strikes depletion layer, electron-hole pairs formed
  • Charge carriers move due to voltage and pulse of current formed
  • This is amplified, read on pulse counter
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
76
Q

Uses of radioisotopes

A
  • medical imaging
  • medical therapy
  • food irradiation
  • radioactive tracers
  • carbon dating
  • industry
  • smoke detectors
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
77
Q

Artificial radioactivity

A
  • most non-radioactive isotopes can be made radioactive by bombarding with neutrons
  • done in nuclear reactor
  • called artificial radioactive isotopes
  • most of isotopes used in medicine and industry reproduced in this way
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
78
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 12 grams of carbon

This number is 6.02x10²³ (Avogadro’s Number)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
79
Q

Nuclear Fission

A

-Nuclear Fission is the splitting up of a large nucleus into two smaller nuclei of roughly the same size

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
80
Q

Fission - how

A
  • the large nucleus is bombarded with neutrons

- v large amounts of energy produced

81
Q

Fission

A
  • More neutrons are produced + may produce further fission; a chain reaction
  • There must be certain amount of material available in order for fission to occur; critical size or mass
  • Uranium and Plutonium both undergo fission when bombarded with fast or slow neutrons
  • They are more likely to react with slow neutrals
  • They are called fissile materials
82
Q

Fissile materials

A
  • Uranium and Plutonium both undergo fission when bombarded with fast or slow neutrons
  • They are more likely to react with slow neutrals
  • They are called fissile materials
83
Q

Critical size or mass

A

-There must be certain amount of material available in order for fission to occur; critical size or mass

84
Q

Chain reaction

A

-More neutrons are produced + may produce further fission; a chain reaction

85
Q

Fission Bomb - other name

A

-Also known as an Atomic bomb

86
Q

Fission Bomb

A

-If two pieces of fissile material of subcritical mass are v suddenly brought together, an uncontrolled chain reaction will occur w/ an enormous release of energy

87
Q

What is used in fission bombs

A

Either Plutonium-239 or Uranium-235 is used

88
Q

Fission reactor

A
  • Fuel
  • Moderator
  • Control rods
89
Q

Fission reactor - fuel

A

-natural uranium, or slightly enriched uranium with U-235

90
Q

Fission reactor - moderator

A
  • Graphite or heavy water
  • Slows down neutrons so further fission will occur (instead of being absorbed by the U-238)
  • increases rate of fission
91
Q

Fission reactor - control rods

A
  • Steel with cadmium or boron
  • Absorb neutrons (this is how it affects the rate of the reaction)
  • placing them in core slows down or stops reaction, depending on desired result
92
Q

Fission reactor

2

A
  • Shielding
  • Coolant
  • Heat exchanger
93
Q

Diagrams you need to know

A

On ppt slide

94
Q

Fission reactor - shielding

A

-Stops radiation from escaping

95
Q

Fission reactor - coolant

A

-Takes heat from core to heat exchanger

96
Q

Fission reactor - heat exchanger

A

-Uses heat to produce steam, which drives a turbine to generate electricity

97
Q

Environmental impact

A
  • Mining
  • Containment of radioactive material
  • Reprocessing
  • Radioactive waste
98
Q

Environmental impact - mining

A

mining of uranium ore releases radon gas which can cause lung cancer

99
Q

Environmental impact - Containment of radioactive material

A

accidents are rare, but can happen, material can get into atmosphere eg. Chernobyl

100
Q

Environmental impact - reprocessing

A

spent rods are cooled and transported to be separated of their elements, transport is difficult

101
Q

Environmental impact - radioactive waste

A

must be stored for a very long time

102
Q

Fusion - definition

A

-The joining of two small nuclei to form a larger nucleus

  • Two heavy Hydrogen atoms can combine to make a Helium atom
  • Can only occur if force acting on two nuclei is large enough to overcome the coulomb repulsion between them
103
Q

When can fusion occur

A

Can only occur if force acting on two nuclei is large enough to overcome the coulomb repulsion between them

104
Q

Fusion

A
  • When fusion occurs, energy is released, can keep reaction going
  • No-one has had a controlled fusion reaction yet
  • Hydrogen bomb is an uncontrolled fusion reaction
  • Fusion is principal source of the Sun’s energy
105
Q

Fusion vs Fission

A
  • Less radioactive waste
  • No possibility of uncontrolled reaction
  • Fuel, deuterium, cheap and easy to get from oceans
106
Q

E = mc²

A
  • Einstein spoke of the relationship between mass and energy in his Special theory of Relativity
  • Mass can be converted into energy, energy can be converted into mass
  • Mass must be expressed in kilograms
107
Q

Mass-Energy Conversion

A
  • If mass of products is greater than that of reactants, energy is supplied
  • If mass of products less than that of reactants, energy is supplied
  • Energy released as kinetic energy or gamma rays
108
Q

Cockcroft and Walton

A
  • in 1932, these scientists performed first nuclear reaction produced by artificially accelerated particles
  • Also first verification of Einstein’s equation E=mc²
  • Won Nobel Prize in 1951
109
Q

Ionising Radiation

A

-Any radiation that will knock off the outer electron of atoms

  • α-radiation, β-radiation, γ-radiation, x-rays are examples
  • All of these are harmful to the human body
  • Exposure to radiation should be limited
110
Q

Ionising Radiation - Amount of damage done depends on:

A
  • Type of radiation
  • Activity of the source
  • Duration of exposure
  • Part of the body exposed
111
Q

Ionising Radiation - can cause

A
  • Skin burns like sunburn
  • Cataracts on eyes
  • Leukaemia (blood cancer)
  • Other cancers
  • Genetic defects in children born to exposed people
  • Death
112
Q

Background radiation

A

-We are all exposed to radiation called bg radiation

113
Q

What bg radiation comes from

A
  • Outer space (cosmic rays)
  • Rocks in the Earth’s crust (granite gives off radon gas which can cause lung cancer)
  • Man-made radioactive materials
114
Q

Precautions when using Ionising Radiation

A
  • Estimate dose rate, and monitor it
  • Minimise time spent exposed
  • Wear protective clothing
  • Use shielding over radioactive sources
  • Keep as far away from source as possible
  • Do not eat, drink or smoke
  • Use tongs for handling
115
Q

Measuring Bg radiation

A
  • Use a GM tube
  • Switch on scaler
  • Set voltage supply to its lowest value
  • Allow tube to warm up
  • Set tube to its operating voltage
  • Measure bg count in 100 sec
  • Note how count varies - random nature of radiation
116
Q

Outline Einstein’s explanation of the photoelectric effect/law

A

hf = Φ + 1/2mv²

  • Light travels in photons
  • Each photon gives all of its energy to one electron
  • If energy is greater than work function, electron is emitted
117
Q

Explain how electrons are produced in an x-ray tube

A

-produced by thermionic emission (at cathode)

118
Q

explain how electrons are accelerated in an x-ray tube

A

-accelerated through a high voltage

119
Q

what are x-rays?

A

Photons/electromagnetic radiation with high energy/short wavelength/high frequency

120
Q

Describe how a photocell conducts current (6)

A
  • Light of suitable freq falls on cathode

- Electrons are emitted

121
Q

Forces acting on drop of oil when it is stationary

A

force of weight down
equal force up

Fe and Fg?

122
Q

When does the photoelectric effect occur?

A

when a photon/light/em radiation strikes a surface with a suitable freq/energy

123
Q

How x-rays are produced in x-ray tube

A

-diagram

  • electrons produced by thermionic emission at cathode
  • high voltage applied to electrons
  • electrons strike target and produce X-rays
124
Q

demonstrate photoelectric effect

A

experiment

125
Q

How are x-rays produced?

A

accelerated electrons strike a metal target/anode

126
Q

Explain why a current does not flow in the photocell when freq of the light is less than (eg. 5.2x10¹⁴ Hz)

(where line on graph of I vs freq crosses x-axis)

A

freq less than threshold freq

127
Q

How was intensity of light varied in testing relationship between current flowing in photocell and intensity of light incident on photocell

A

Vary distance from light source to photocell

128
Q

What conclusion about the nature of light can be drawn from investigation f current flowing in photocell and intensity of light incident on it. + Sketch of graph obtained from readings

A

X-axis: 1/d² (or intensity)

Y-axis: I

directly proportional starting from origin

Conclusion: light is made up of photons, light has a corpuscular nature, light has not got a wave nature

129
Q

two ways of deflecting a beam of electrons

A

by means of an electric field and a magnetic field

130
Q

how are electrons accelerated in a cathode ray tube?

A

by a large pd/voltage/electric field

131
Q

Who discovered x-rays?

A

Rontgen

132
Q

how are electrons emitted from cathode in x-ray tube

A

by thermionic emission/heating the cathode

133
Q

applications of photoelectric effect

A
  • photography
  • photocell
  • burglar alar
  • automatic door
  • sound track in film
134
Q

name a device used to detect beta-radiation/ionising radiations/radioactivity/activity of a sample and explain its principle of operation

A
  • Geiger-Muller tube/solid-state detector

- ionisation/current flows / ( gas is) ionised (and a pulse of charge/current flows)

135
Q

describe rutherford’s experiment to investigate structure of the atom

A
  • diagram
  • alpha particle, gold foil, zinc sulfide/screen
  • alpha particles fired at foil
  • some passed straight through, some deflected, some rebounded
136
Q

conclusions about nature of atom Rutherford made/Rutherford’s model of the atom

A
  • mostly empty space

- small/dense/positive core

137
Q

explain, using Bohr model, how line spectra are formed

A
  • energy supplied
  • electrons move to a higher/excited energy level
  • electrons fall down
  • emitting light
138
Q

spectrometer diagram

A

in notes

139
Q

How a spectrometer and a diffraction grating can be used to observe a (i) line spectrum (ii) continuous spectrum

A

(i) vapour lamp

(ii) filament bulb/white light

140
Q

define fission (nuclear fission)

A

the breaking up of a large nucleus into smaller nuclei with the release of energy and neutrons

141
Q

How many of the neutrons emitted in a fission reaction must cause a further fission so that reaction is self-sustaining and safe? explain your answer

A

1

> 1: uncontrolled reaction
< 1: chain-reaction ending

142
Q

name a detector of radiation and describe with a labelled diagram its principle of operation

A
  • geiger-muller tube
  • diagram: cathode, wire anode, low pressure inert gas, case

-ionisation of gas

or

  • solid-state detector
  • diagram: cathode, anode, semiconductor material, housing

-free electrons + holes produced

143
Q

define the becquerel

A

one disintegration per second

144
Q

compare alpha, beta, gamma emissions in terms of: (A) penetrating ability, (B) deflection in a magnetic field

A

(A) gamma (most penetrating) > beta > alpha (least penetrating)

(B)

  • alpha, beta deflected, gamma not deflected
  • alpha and beta deflected in opposite directions
145
Q

three quantities that are conserved in nuclear reactions

A

momentum
charge
mass-energy
nucleons

146
Q

in initial observations of beta-decay, not all three quantities appear to be conserved. What was the solution to this contradiction?

A

Proposal/discovery of the neutrino

neutrino had he missing momentum and energy

147
Q

list of fundamental forces of nature in increasing order of their strength

A

gravitational < weak nuclear < electromagnetic < strong nuclear

148
Q

which fundamental force of nature is involved in beta-decay

A

weak nuclear

149
Q

why are new particles produced in collision of two protons and two charged pi mesons

A

energy is converted into mass ( E=mc^2)

150
Q

2011 (D) - suitable detector for paper passing between a radioisotope and detector

  • how reading on detector may vary as paper passes by
  • why Am-241 which emits alpha-particles not suitable for this process
A
  • solid state detector/GM tube
  • count rate would decrease with increasing paper thickness
  • paper would block alpha-particles
151
Q

how x-rays differ from light rays

A

x-rays penetrate matter/cause ionisation

152
Q

when electrons hit target in an x-ray tube, only a small % of their energy is converted into x-rays. What happens to the rest of their energy and how does this influence type of target used?

A
  • converted to heat

- target material must have high melting point

153
Q

how are alpha particles produced?

A

americium is radioactive/disintegrates

154
Q

why dont alpha particles not post a health risk in smoke detectors

A

poor penetrators

155
Q

why americium-241 does not exist naturally

A

not a member of a decay series

half life is short

156
Q

diagram to show how cockroft and walton accelerated protons

A

diagram 2007 q10 a

157
Q

compare properties of electron with that of a positron

A

both have equal mass, charges equal, charges opposite in sign

158
Q

what happens when an electron meets a positron?

A

pair annihilation

gamma rays emitted

energy released

159
Q

describe the Bohr model of the atom

A
  • nucleus

- electrons in orbit/shells/energy levels

160
Q

why cant neutrons be accelerated using high voltages

A

neutrons are not charged

alpha particles and protons can be as they are charged

161
Q

advantage of circular accelerators over linear accelerators

A
  • progressively increasing energy/speed attainable

- more compact

162
Q

why are new particles produced in an accelerator when two high speed protons collide

A

kinetic energy of the protons converted into mass of new particles

163
Q

fundamental fource of nature that holds the nucleus together

A

strong nuclear

164
Q

application of radioactivity

A

smoke detectors, carbon dating, tracing leaks

165
Q

application of fission

A

generating electrical energy, bombs

166
Q

what is ionisation

A

the charging of a neutral atom / when atom loses or gains electrons

167
Q

experiment to demonstrate ionising effect of radioactivity

A

apparatus: radioactive source and charged gold leaf electroscope
procedure: bring radioactive source close to cap
observation: leaves collapse
conclusion: electroscope neutralised by ionised air

168
Q

why are large temps required for fusion to occur?

A
  • nuclei are positively charged

- force of repulsion must be overcome/large energy necessary to join them together

169
Q

writing equations for nuclear reaction

A

know how to

2006 q8

170
Q

condition necessary for controlled nuclear fusion to take place on earth

A

-large initial temp/energy required to start the reaction

171
Q

benefit of terrestrial fusion reactor

A
  • fuel: plentiful/readily available/cheap
  • energy: vast energy released
  • pollution: no/little radioactive waste
172
Q

why is a fission reactor more viable of an energy source than fusion reactor?

A

fission can be more easily controlled

173
Q

source of the sun’s energy

A

fusion reaction / hydrogen gas

174
Q

why are neutrons slowed down in a nuclear fission reactor

A

-only slow neutrons cause fission / to prevent radiative capture

175
Q

positive environmental impact of fission reactors + negative

A

positive: no greenhouse gases, less dependence of fossil fuels, no CO2 emissions etc
negative: radioactive waste, etc

176
Q

types of electromagnetic radiation

A

radio waves, microwaves, infrared waves, visible light, ultraviolet radiation, X-rays, and gamma rays

177
Q

what is a chain reaction + condition necessary for a chain reaction to occur

A

-self-sustaining reaction/reaction where fission neutrons produce further fission (giving more neutrons)

  • mass of fuel present exceeds the critical mass
  • at least one of the neutrons released may cause fission of another nucleus
178
Q

advantage of fusion over fission

A
  • hydrogen fuel from sea is plentiful

- no radioactive waste with fusion/less radioactive waste

179
Q

benefit of nuclear power over fossil fuels

A
  • more energy per kg

- less carbon dioxide produced

180
Q

give an example of a moderator

A

graphite / heavy water

181
Q

how a heat exchanger operates

A

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

182
Q

why use a heat exchanger

A

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

183
Q

cockroft and walton experiment: how protons were produced, how they were accelerated, how alpha-particles detected

A

produced: ionisation/discharge tube
accelerated: high voltage

a-particles detected: flashes/zinc sulphide/screen

184
Q

historical significance of cockroft and walton experiment

A

verified E=mc^2

185
Q

why fusion reactors are not a practical source of energy on earth yet

A

too much energy is required to overcome force of repulsion between nuclei

186
Q

proton, neutron, electron mass in amu/u

A

proton: 1.007276 u
neutron: 1.008665 u
electron: 0.000549 u

187
Q

why light emitted when metal is heated

A

electrons excited/gain energy 3 jump to higher energy state 3 return to lower state 3 emit energy / emr /i.r / light / photon

188
Q

eV formula (not on log tables!!)

A

eV = hc/λ

eV = 1/2 mv²

189
Q

u in eV

A

1 u = 931 MeV

190
Q

Explain what is meant by the statement: “Zinc has a threshold frequency of 1.04 × 1015 Hz”

A

below this frequency e.m.r. /photons will not cause emission of electrons (from zinc surface)

191
Q

Explain what happens during nuclear fission.

A

-large nucleus splits 3 into two smaller nuclei 3 with the emission of energy / neutrons

192
Q

decay constant

A

wavelength

193
Q

Describe an experiment to demonstrate how the current through a photocell can be increased.

A

apparatus: photocell, meter, light source, (power supply)
arrangement: as shown

procedure: bring light source closer (to photocell)
observation: current in circuit increases

diagram 2012 q12 d

194
Q

Name the naturally occurring radioactive gas which seeps into buildings from underground rocks and which can cause lung cancer.

A

radon (gas)

195
Q

decay constant unit

A

s^-1

196
Q

half life (T1/2) unit

A

seconds

197
Q

Writing a proton in equations

A

written as a hydrogen atom

¹₁H

198
Q

Uranium reaction in a nuclear reactor eg?

A

²³⁵U + ¹₀n –> ¹⁴¹Ba + Kr + 3¹₀n

199
Q

graph of time vs activity - how to find half life using graph

A

find the time at which activity halves, and that is the half life

LC Physics (25 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions