Unit 6 Flashcards
1
Q
light
A
- described as either particle of wave
- exhibits characteristics of both
- when it interacts with solid matter, it behaves as a particle
- when it travels through empty space, light travels as a wave
2
Q
support for wave nature of light
A
-Huygens
-Young: constructive and destructive interference
Maxwell: part of EM spectrum
3
Q
support for particle nature of light
A
-Newton
-Planck: atoms are quantized
Einstein: photoelectric effect
4
Q
what is the energy of a photon related to?
A
its frequency. as frequency increases, energy increases, and thus they are directly proportional
5
Q
what did de Broglie show?
A
that all matter exhibits wave properties
6
Q
“quantized” electron
A
an electron that is quantized because it can only exist at certain energy levels around the nucleus of an atom
7
Q
material particles and light have both…
A
wave properties and particle properties
8
Q
models
A
- not true, but useful
- useful model of atom must be consistent with the model for light
9
Q
what is the source of light
A
most light has its source in the motion of electrons within the atom
10
Q
2 primary models of light
A
the particle model and the wave model
11
Q
quantum
A
the fundamental “size” unit; the smallest amount of anything.
-one quantum of light energy is called a photon
12
Q
photon
A
1 quantum of light energy
13
Q
energy of every photon
A
E = hf
14
Q
planck’s constant
A
h = E (energy of a photon)/f (frequency)
15
Q
photoelectric effect
A
Metals eject electrons when light of a certain frequency or energy hits them. The electrons are only ejected at certain frequencies.
-This supports the particle model of light.
16
Q
all particles have a wavelength that is related to the momentum of particles by
A
wavelength = h/momentum
17
Q
electron microscope
A
wavelength of electron beams is typically thousands of time shorter than the wavelength of visible light, so the electron microscope is able to distinguish details thousands of times smaller than is possible with optical microscopes
18
Q
an electron has a different amount of energy when…
A
it is in different orbits around a nucleus
-electrons in an atom normally occupy the lowest energy levels avaliable
19
Q
de Broglie’s theory of matter waves
A
electron orbits exist only where an electron wave closes in on itself in phase
20
Q
what is the radii of the electron orbits in the Bohr model of the atom determined by?
A
the amount of electric charge in the nucleus
21
Q
bohr model
A
solved mystery of the atomic spectra of the elements
22
Q
ionization energy
A
energy needed to knock the electron out of an atom completely
23
Q
quantum mechanics
A
the study of the motion of particles in the same microworld of atoms and nuclei
24
Q
quantum physics
A
branch of physics that is the general study of the mircroworld of photons, atoms, and nuclei
25
what are the subatomic interactions described by quantum mechanics are governed by?
laws of probability, not laws of certainty
26
what does predictability in orderly systems depend on?
knowledge of initial conditions
27
describe what the photoelectric effect suggests about the way light interacts with matter
light interacts with matter as a stream of particle-like photons
28
why does violet light eject electrons from a certain photosensitive surface, whereas red light has no effect on that surface?
violet light carries enough energy to free an electron from the metal, and violet light can eject a few electrons. But red, which as a low frequency, does not have the energy needed to eject an electron
-Using the equation Energy = hf; blue light has higher energy because it has a shorter wavelength and a higher frequency.
29
how does the energy of a photon compare with the difference in energy levels of the atom from which it is emitted
the energy of a photon is exactly equal to the differences in the energy levels in the atom.
30
In the photoelectric effect, does brightness or frequency determine the kinetic energy of the ejected electrons?
The KE of the ejected electrons is determined by the frequency of the light hitting the metal.
31
In the photoelectric effect, does brightness or frequency determine the number of ejected electrons?
The number of electrons that is ejected is determined by the brightness of the light hitting the metal because brightness is related to total energy available.
32
purpose of neutrons in a nucelus
the principal role of neutrons in an atomic nucleus is to act as the glue that holds a nucleus together
33
strong force
- binds protons to protons and neutrons to protons
- relative strength 1
- range within the nucleus
34
electromagnetic force
- protons repel each other
- relative strength 1/137
- range infinite
35
gravity
- attracts all particles with mass to all other particles with mass
- relative strength 6*10^-39
- range infinite
36
neutron decay
- neutrons are not completely stable and spontaneously decay into a proton and an electron at a regular rate
- not made of a electron and a neutron, but can change into them through the decay process
- when decay occurs -> energy released as radiation
37
alpha radiation
- positive charge
- composition: 2 protons and 2 neutrons
- relative mass 8000
- stopped by a few sheets of paper
38
beta radiation
-negative charge
-composition: electron
relative mass 1
-stopped by few sheets of aluminum foil
-electron ejected from the nucleus when the neutron is transformed into a proton
39
gamma radiation
- neutral charge
- composition: photon
- relative mass: massless
- stopped by lead or other heavy shielding
40
why are gamma rays so hard to stop?
gamma rays have no charge and so do not interact with charged particles. Also they are massless so they are moving v. quickly
41
how does carbon dating work?
c-14 exists in small amounts on earth and is incorporated int every living thing.
- when organisms die, they stop taking in c-14, but the organism continues to decay with a half-life of 5730 years
- because the percentage of c-14 that existed when the organism died how quickly it decays is known, can tell how long the organism has been dead
42
what is a feature of quantum mechanics
particles held close together have large kinetic energy and tend to fly apart
-presence of neutron adds to nuclear attraction and keeps protons from flying apart
43
what is the proportion of neutrons to protons?
in light elements 1:1. in heavy elements, there are more neutrons than protons
44
what is a factor that limits how many stable nuclei can exist?
the instability of neutrons
45
radioactive
particles that decay by spontaneously emitting charged particles and energy.
46
what is radioactivity inside the atomic nuclei governed by?
mass-energy equivalence
| -particles decay spontaneously only when their combined products have less mass after decay than before
47
radiation
charged particles and energy emitted by an unstable nucleus or particle
48
what are the three distinct types of radiation emitted by atoms of radioactive elements?
alpha particles, beta particles, and gamma rays
49
ion
when there is a difference in the number of electrons and protons, then the atom is charged
50
isotope
a form of an element having a particular number of neutrons in the nuclei of its atoms
-isotopes of an element are chemically identical but differ in the number of neutrons
51
atomic number
the number of protons
52
atomic mass number
the total number of nucleons in the nucleus
53
the rates of radioactive decay appear to be...
absolutely constant, unaffected by any external conditions
54
transmutation
the changing of one element to another
55
alpha decay
energy released -> gamma radiation, kinetic energy of alpha particle and the kinetic energy of the atom
56
beta-decay
emits beta particle
57
how have radioactive isotopes of elements been produced?
by bombarding the elements with neutrons and other particles
58
what are sources of natural radiation?
cosmic rays, earth minerals, and radon in the air
59
cosmic rays
some penetrate the atmosphere, mostly in the form of secondary particles
60
explain the factor that determine the penetrating power of radiation
depends on its speed and its charge
61
explain the effect of radioactive decay on an isotope
when an isotope undergoes alpha or beta decay, it changes to a different element
62
which elements have been produced through artificial transmutation?
elements beyond uranium
63
when is a neutron unstable?
when it is by itself
64
what is a transuranic element
an element that has been produced through artificial transmutation. an element beyond uranium in the periodic table
65
why are there no ore deposits of transuranic elements on earth?
all these elements have half-lives that are much less than the age of the earth
66
what is a radioactive tracer
a radioactive isotope placed in a system and monitored
67
why is radiation more intense at high altitudes and near earth's poles?
less atmospheric absorption results in less shielding
68
If protons repel each other, why don't nuclei just fall apart?
Nuclei are held together by the strong force generated by the presence of protons and neutrons. Without the neutrons, the strong force would not be strong enough to hold the nuclei together against the electromagnetic repulsion.
69
nuclear fission reactor
controls the rate of nuclear decay so that manageable amounts of energy are released as needed.
-most energy generated: form of heat, which boils water to drive turbines and generate electrcity
70
nuclear fission
is the decay of one atomic nucleus into two smaller atoms
71
when does nuclear fission occur
occurs when the electromagnetic repulsion overcomes the strong nuclear force and pushes the nucleus apart
72
chain reaction
a self-sustaining reaction in which one reaction event stimulates one or more additional reaction events to keep the process going
73
critical mass
the amount of mass for which each fission event produces, on the average, on additional fission event
74
subcritical mass
one in which the chain reaction dies out
75
supercritical mass
one in which the chain reaction builds up explosively
76
3 main parts of a nuclear fission reactor
the nuclear fuel (uranium) combined with a moderator, the control rods, and water
77
breeder reactor
is a nuclear fission reaction that produces more nuclear fuel than it consumes
-converts a non-fissionable uranium isotope into a fissionable plutonium isotope
78
mass spectrometer
accurately measures the masses of ions of isotopes of various elements
79
nuclear fusion
process where the nuclei of light atoms fuse
| -energy is released when light nuclei fuse together
80
what is the role of electrical forces in nuclear fission?
nuclear fission occurs when the repelling electrical forces within a nucleus overpower the attracting nuclear strong forces
81
what is the role of a neutron in nuclear fission?
the absorption of a neutron by a uranium nucleus supplies enough energy to cause an elongation which starts the fission of an uranium atom
82
of what use are the neutrons that are produced when a nucleus undergoes fission?
the new neutrons can cause the fissioning of two or three other nuclei, releasing from 4-9 more neutrons, that cause more fissioning and starts a chain reaction
83
what is the effect of putting a little Pu-239 with a lot of U-238 in a reactor?
the fissioning of plutonium liberates neutrons that convert the abundant non-fissionable U-238 into more of the fissionable Pu-239
84
what are the conditions necessary to sustain a chain reaction?
requires that the uranium contain a higher percentage of U-235 than occurs naturally
85
equation for the fission of uranium-235
1 neutron + U-235 —> krypton-91 + barium-142 + 3 neutrons
86
pros and cons for nuclear power reactors.
Pros: reactors are cheap, plentiful, and efficient.
Cons: they generate radioactive waste that must be stored, limited supply of fissionable materials.
87
major components of a nuclear power plant.
Reactor vessel: a place where fission reactions will occur.
Fuel: radioactive material that will undergo fission.
Control rods: non-reactive material that stop neutrons from causing further reactions.
Steam: generated by heat of nuclear reactions.
Turbines: turned by steam.
Generator: connected to turbines to generate electrical energy.
Condenser: turns steam back into water.
88
Why are fission products radioactive?
When the neutrons hit the fuel, it becomes part of the nucleus, so the remaining fragments have extra neutrons.
89
how iron is related to fission, fusion, and energy production in nuclear reactions?
Elements smaller than iron can be fused to produce energy while elements larger than iron can be fissioned to produce energy.
90
which will leak more neutrons: two separate pieces of uranium or the same pieces stuck together?
two separate pieces because smaller pieces have more surface area per volume
91
will a supercritical chain reaction be more likely in two separate pieces of u-235 or in the same pieces stuck together
same pieces stuck together
92
why are the fission-fragment elements radioactive?
because they are neutron rich so they are very loosely bound and stable
93
is the mass per nucleon of a nucleus greater than, less than, or the same as the mass of a nucleon outside a nucleus?
the mass per nucleon of a nucleus is less than the mass of the individual nucleons
94
why does iron not yield energy if fused with something else or if fissioned?
iron has the least mass per nucleon so it will not fission or fuse into a denser packed element
95
what becomes of the loss in mass when light atoms fuse to become heavier ones
when light atoms are fused the mass becomes kinetic energy
