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ConcepTest 27.1ConcepTest 27.1 PhotonsPhotons
400 nm 500 nm 600 nm 700 nm
Which has more energy, a Which has more energy, a
photon of:photon of:
1) red light
2) yellow light
3) green light
4) blue light
5) all have the same energy
The photon with the highest frequencyhighest frequency has the most energymost energy
because E = hf = hc/ (recall that cc = = ff ). So a higherhigher
frequencyfrequency corresponds to a lower wavelengthlower wavelength. The highest
energy of the above choices is blueblue.
ConcepTest 27.1ConcepTest 27.1 PhotonsPhotons
400 nm 500 nm 600 nm 700 nm
Which has more energy, a Which has more energy, a
photon of:photon of:
1) red light
2) yellow light
3) green light
4) blue light
5) all have the same energyE = h f
ConcepTest 27.2aConcepTest 27.2a Photoelectric Effect IPhotoelectric Effect I
If the cutoff frequency for light in
the photoelectric effect for metal
B is greater than that of metal A.
Which metal has a greater work
function?
1) metal A
2) metal B
3) same for both
4) WW00 must be zero for one of the metals
f
KE
f0
A greatergreater cutoff frequencycutoff frequency means a higherhigher
energyenergy is needed to knock out the electron. But
this implies that the work function is greaterwork function is greater,
since the work function is defined as the
minimum amount of energy needed to eject an
electron.
ConcepTest 27.2aConcepTest 27.2a Photoelectric Effect IPhotoelectric Effect I
If the cutoff frequency for light in
the photoelectric effect for metal
B is greater than that of metal A.
Which metal has a greater work
function?
1) metal A
2) metal B
3) same for both
4) WW00 must be zero for one of the metals
f
KE
f0
Follow-up:Follow-up: What would you expect to happen to the work function What would you expect to happen to the work function of a metal if the metal was heated up?of a metal if the metal was heated up?
A metal surface with a work A metal surface with a work
function of function of WW00 = hc/550 nm = hc/550 nm
is struck with is struck with blue lightblue light and and
electrons are released. If electrons are released. If
the the blue lightblue light is replaced by is replaced by
red lightred light of the same of the same
intensity, what is the result?intensity, what is the result?
1) emitted electrons are more energetic
2) emitted electrons are less energetic
3) more electrons are emitted in a given time interval
4) fewer electrons are emitted in a given time interval
5) no electrons are emitted
ConcepTest 27.2bConcepTest 27.2b Photoelectric Effect IIPhotoelectric Effect II
Red lightRed light has a wavelength of about 700 nm700 nm. The
cutoff wavelength is 550 nm550 nm (yellow lightyellow light), which is
the maximum wavelengthmaximum wavelength to knock out electrons.
Thus, no electrons are knocked outno electrons are knocked out.
A metal surface with a work A metal surface with a work
function of function of WW00 = = hchc/550 nm/550 nm
is struck with is struck with blue lightblue light and and
electrons are released. If electrons are released. If
the the blue lightblue light is replaced by is replaced by
red lightred light of the same of the same
intensity, what is the result?intensity, what is the result?
400 nm 500 nm 600 nm 700 nm
energyenergylowlowhighhigh
EE = = hchc / /
1) emitted electrons are more energetic
2) emitted electrons are less energetic
3) more electrons are emitted in a given time interval
4) fewer electrons are emitted in a given time interval
5) no electrons are emitted
ConcepTest 27.2bConcepTest 27.2b Photoelectric Effect IIPhotoelectric Effect II
ConcepTest 27.2cConcepTest 27.2c Photoelectric Effect IIIPhotoelectric Effect IIIA metal surface is struck with A metal surface is struck with
light of light of = 400 nm = 400 nm, releasing , releasing
a a stream of electrons. If the of electrons. If the
400 nm400 nm light is replaced by light is replaced by
= 300 nm= 300 nm light of the same light of the same
intensity, what is the result?intensity, what is the result?
1) more electrons are emitted in a given time interval
2) fewer electrons are emitted in a given time interval
3) emitted electrons are more energetic
4) emitted electrons are less energetic
5) none of the above
A reducedreduced wavelengthwavelength means a higherhigher frequencyfrequency, which
in turn means a higher energyhigher energy. So the emitted
electrons will be more energeticmore energetic, since they are now
being hit with higher energy photons.
ConcepTest 27.2cConcepTest 27.2c Photoelectric Effect IIIPhotoelectric Effect IIIA metal surface is struck with A metal surface is struck with
light of light of = 400 nm = 400 nm, releasing , releasing
a a stream of electrons. If the of electrons. If the
400 nm400 nm light is replaced by light is replaced by
= 300 nm= 300 nm light of the same light of the same
intensity, what is the result?intensity, what is the result?
1) more electrons are emitted in a given time interval
2) fewer electrons are emitted in a given time interval
3) emitted electrons are more energetic
4) emitted electrons are less energetic
5) none of the above
Remember that cc = = ff and that E = h fE = h f
A metal surface is struck with A metal surface is struck with
light of light of = 400 nm = 400 nm, releasing , releasing
a stream of electrons. If the a stream of electrons. If the
light light intensityintensity is increased is increased
((without changing without changing ), what is ), what is
the result?the result?
1) more electrons are emitted in a given time interval
2) fewer electrons are emitted in a given time interval
3) emitted electrons are more energetic
4) emitted electrons are less energetic
5) none of the above
ConcepTest 27.2dConcepTest 27.2d Photoelectric Effect IVPhotoelectric Effect IV
A metal surface is struck with A metal surface is struck with
light of light of = 400 nm = 400 nm, releasing , releasing
a stream of electrons. If the a stream of electrons. If the
light light intensityintensity is increased is increased
((without changing without changing ), what is ), what is
the result?the result?
1) more electrons are emitted in a given time interval
2) fewer electrons are emitted in a given time interval
3) emitted electrons are more energetic
4) emitted electrons are less energetic
5) none of the above
A higher intensityhigher intensity means a more photonsmore photons, which in turn
means more electronsmore electrons.. On average, each photon
knocks out one electron.
ConcepTest 27.2dConcepTest 27.2d Photoelectric Effect IVPhotoelectric Effect IV
ConcepTest 27.4ConcepTest 27.4 IonizationIonization
How much energy does it How much energy does it
take to ionize a hydrogen take to ionize a hydrogen
atom in its ground state?atom in its ground state?
1) 0 eV
2) 13.6 eV
3) 41.2 eV
4) 54.4 eV
5) 108.8 eV
The energy of the ground state is the
energy that binds the electron to the
nucleus. Thus, an amount equal to this
binding energy must be supplied in order
to kick the electron out of the atom.
ConcepTest 27.4 ConcepTest 27.4 IonizationIonization
How much energy does it How much energy does it
take to ionize a hydrogen take to ionize a hydrogen
atom in its ground state?atom in its ground state?
1) 0 eV
2) 13.6 eV
3) 41.2 eV
4) 54.4 eV
5) 108.8 eV
2
2
1 nZ
EEn
Follow-up:Follow-up: How much energy does it take to change a He How much energy does it take to change a He++ ion ion into a Heinto a He++++ ion? Keep in mind that ion? Keep in mind that ZZ = 2 for helium. = 2 for helium.
ConcepTest 27.5aConcepTest 27.5a Atomic Transitions IAtomic Transitions I
n = 1
n = 2
n = 3
n = 5n = 4
1) 2 5
2) 5 3
3) 8 5
4) 4 7
5) 15 7
For the possible transitions For the possible transitions
shown, for which transition will shown, for which transition will
the electron the electron gaingain the most the most
energy?energy?
ConcepTest 27.5aConcepTest 27.5a Atomic Transitions IAtomic Transitions I
n = 1
n = 2
n = 3
n = 5n = 4
1) 2 5
2) 5 3
3) 8 5
4) 4 7
5) 15 7
The electron must go to a higherhigher orbit
(higher higher nn) in order for the electron to
gain energy.
Because of the 1/n2 dependence:
E2 – E5 > E4 – E7
For the possible transitions For the possible transitions
shown, for which transition will shown, for which transition will
the electron the electron gaingain the most the most
energy?energy?
Follow-up:Follow-up: Which transition will Which transition will emitemit the the shortestshortest wavelength photon? wavelength photon?
n = 1
n = 2
n = 3
n = 5n = 4
n = n = 6
The Balmer series for hydrogen The Balmer series for hydrogen
can be observed in the visible part can be observed in the visible part
of the spectrum. Which transition of the spectrum. Which transition
leads to the leads to the reddestreddest line in the line in the
spectrum?spectrum?
1) 3 2
2) 4 2
3) 5 2
4) 6 2
5) 2
ConcepTest 27.5bConcepTest 27.5b Atomic Transitions IIAtomic Transitions II
The transition 3 3 2 2 has the
lowestlowest energyenergy and thus the lowestlowest
frequencyfrequency photon, which
corresponds to the longest longest
wavelengthwavelength (and therefore the
“reddestreddest”) line in the spectrum. n = 1
n = 2
n = 3
n = 5n = 4
n = n = 6
The Balmer series for hydrogen The Balmer series for hydrogen
can be observed in the visible part can be observed in the visible part
of the spectrum. Which transition of the spectrum. Which transition
leads to the leads to the reddestreddest line in the line in the
spectrum?spectrum?
1) 3 2
2) 4 2
3) 5 2
4) 6 2
5) 2
ConcepTest 27.5bConcepTest 27.5b Atomic Transitions IIAtomic Transitions II
Follow-up:Follow-up: Which transition leads to the shortest wavelength photon?
ConcepTest 27.6ConcepTest 27.6 Balmer SeriesBalmer Series
When a broad spectrum of light passes through hydrogen gas at room temperature, absorption lines are observed that correspond only to the Balmer (nf = 2) series. Why
aren’t other series observed?
1) they’re there, but they’re invisible
2) only the Balmer series can be
excited at room temperature
3) the other series have been ionized
4) all the photons have been used up
ConcepTest 27.6 ConcepTest 27.6 Balmer SeriesBalmer Series
When a broad spectrum of light passes through hydrogen gas at room temperature, absorption lines are observed that correspond only to the Balmer (nf = 2) series. Why
aren’t other series observed?
1) they’re there, but they’re invisible
2) only the Balmer series can be
excited at room temperature
3) the other series have been ionized
4) all the photons have been used up
The Balmer series is the only one
that involves wavelengths in the wavelengths in the
visible partvisible part of the spectrum!
Follow-up:Follow-up: From the diagram at right, where in the EM spectrum is the Lyman series located?
ConcepTest 27.7aConcepTest 27.7a Energy Levels IEnergy Levels I
n = 1
n = 2
n = 3
n = 5n = 4
Suppose there is an atom that
contains exactly five energy
levels. How many different
transitions are possible? (Count
only one direction!)
1) 4
2) 5
3) 10
4) 20
5) many more than 20
ConcepTest 27.7aConcepTest 27.7a Energy Levels IEnergy Levels I
n = 1
n = 2
n = 3
n = 5n = 4Just count them! Transitions upwardupward:
n = 1 n = ? 4 transitions
n = 2 n = ? 3 transitions
n = 3 n = ? 2 transitions
n = 4 n = ? 1 transition
This gives a total of This gives a total of 1010 possible ones possible ones.
Suppose there is an atom that
contains exactly five energy
levels. How many different
transitions are possible? (Count
only one direction!)
1) 4
2) 5
3) 10
4) 20
5) many more than 20
(1) (2) (3) (4)
The emission spectrum for the atoms of a gas is shown. Which of the energy level diagrams below corresponds to this spectrum?
ConcepTest 27.7bConcepTest 27.7b Energy Levels IIEnergy Levels II
(1) (2) (3) (4)
Each line in the spectrum corresponds to a transitiontransition between energy levels! Since there are 6 transitions6 transitions shown, there must be 4 levels4 levels. The 2 transitions between the closely spaced levels have less energy, The 2 transitions between the closely spaced levels have less energy, while the other 4 have larger energieswhile the other 4 have larger energies.
The emission spectrum for the atoms of a gas is shown. Which of the energy level diagrams below corresponds to this spectrum?
ConcepTest 27.7bConcepTest 27.7b Energy Levels IIEnergy Levels II
ConcepTest 30.1 ConcepTest 30.1 The NucleusThe Nucleus
There are 82 protons
in a lead nucleus.
Why doesn’t the
lead nucleus burst
apart?
1) Coulomb repulsive force doesn’t act 1) Coulomb repulsive force doesn’t act
inside the nucleusinside the nucleus
2) gravity overpowers the Coulomb 2) gravity overpowers the Coulomb
repulsive force inside the nucleusrepulsive force inside the nucleus
3) the negatively charged neutrons balance 3) the negatively charged neutrons balance
the positively charged protonsthe positively charged protons
4) protons lose their positive charge4) protons lose their positive charge inside inside
the nucleusthe nucleus
5) none of the above5) none of the above
The Coulomb repulsive force is
overcome by the even stronger
nuclear forcenuclear force!
ConcepTest 30.1 ConcepTest 30.1 The NucleusThe Nucleus
There are 82 protons
in a lead nucleus.
Why doesn’t the
lead nucleus burst
apart?
1) Coulomb repulsive force doesn’t act 1) Coulomb repulsive force doesn’t act
inside the nucleusinside the nucleus
2) gravity overpowers the Coulomb 2) gravity overpowers the Coulomb
repulsive force inside the nucleusrepulsive force inside the nucleus
3) the negatively charged neutrons balance 3) the negatively charged neutrons balance
the positively charged protonsthe positively charged protons
4) protons lose their positive charge4) protons lose their positive charge inside inside
the nucleusthe nucleus
5) none of the above5) none of the above
What weighs more, an
electron and a proton,
or a hydrogen atom?
1) electron and proton1) electron and proton
2) hydrogen atom 2) hydrogen atom
3) both the same3) both the same
ConcepTest 30.2a ConcepTest 30.2a Binding Energy IBinding Energy I
What weighs more, an
electron and a proton,
or a hydrogen atom?
1) electron and proton1) electron and proton
2) hydrogen atom 2) hydrogen atom
3) both the same3) both the same
ConcepTest 30.2a ConcepTest 30.2a Binding Energy IBinding Energy I
The total energy (or mass) of a hydrogen atom
must be lessless than the energies (or masses) of the
electron plus the proton individually in order for
the electron to be bound.
ConcepTest 30.2b ConcepTest 30.2b Binding Energy IIBinding Energy II
What is the total energy
(or mass) of the hydrogen
atom in its ground state?
1) 13.6 eV1) 13.6 eV
2) 2) mmppcc22 + + mmeecc22 + 13.6 eV + 13.6 eV
3) 3) mmppcc22 + + mmeecc22
4) 4) mmppcc22 + + mmeecc22 – 13.6 eV – 13.6 eV
The total energy (or mass) of a hydrogen atom
must be lessless than the energies (or masses) of the
electron plus the proton individually in order for
the electron to be bound. The mass difference is The mass difference is
the binding energy.the binding energy.
ConcepTest 30.2b ConcepTest 30.2b Binding Energy IIBinding Energy II
What is the total energy
(or mass) of the hydrogen
atom in its ground state?
1) 13.6 eV1) 13.6 eV
2) 2) mmppcc22 + + mmeecc22 + 13.6 eV + 13.6 eV
3) 3) mmppcc22 + + mmeecc22
4) 4) mmppcc22 + + mmeecc22 – 13.6 eV – 13.6 eV
1) the 2 neutrons and 1 proton
2) the tritium nucleus
3) they both weigh the same
4) it depends on the specific
isotope of tritium
On a balance scale, you put
2 neutrons and 1 proton on
one side and you put a
tritium nucleus (3H) on the
other. Which side weighs
more?
ConcepTest 30.2c ConcepTest 30.2c Binding Energy IIIBinding Energy III
The mass of the 2 neutrons and
1 proton is lessless when they are
bound together as tritium. The The
mass difference is the binding mass difference is the binding
energy.energy.
need to need to addadd 8.5 MeV8.5 MeV to balance scaleto balance scale
1) the 2 neutrons and 1 proton
2) the tritium nucleus
3) they both weigh the same
4) it depends on the specific
isotope of tritium
On a balance scale, you put
2 neutrons and 1 proton on
one side and you put a
tritium nucleus (3H) on the
other. Which side weighs
more?
ConcepTest 30.2c ConcepTest 30.2c Binding Energy IIIBinding Energy III
1) removing a proton takes more energy
2) removing a neutron takes more energy
3) both take the same amount of energy
Does it take more
energy to remove
one proton or one
neutron from 16O?
ConcepTest 30.3 ConcepTest 30.3 Separation EnergySeparation Energy
Removing a proton takes lessless energy because the
repulsive Coulomb forcerepulsive Coulomb force between positively charged
protons helps to push the proton out of the nucleus.
Remember that neutrons are uncharged.
1) removing a proton takes more energy
2) removing a neutron takes more energy
3) both take the same amount of energy
Does it take more
energy to remove
one proton or one
neutron from 16O?
ConcepTest 30.3 ConcepTest 30.3 Separation EnergySeparation Energy
A radioactive nucleus
undergoes gamma decay.
How large would you
expect the energy of the
emitted photon to be?
1) less than 13.6 eV1) less than 13.6 eV
2) 13.6 eV2) 13.6 eV
3) hundreds of eV3) hundreds of eV
4) millions of eV4) millions of eV
5) billions of eV5) billions of eV
ConcepTest 30.5 ConcepTest 30.5 Radioactive Decay EnergyRadioactive Decay Energy
The binding energy of nuclei is of the
order several MeVseveral MeV (millions of eV).
So, we would expect the energy of
gamma decay to be in the same ballpark.
A radioactive nucleus
undergoes gamma decay.
How large would you
expect the energy of the
emitted photon to be?
1) less than 13.6 eV1) less than 13.6 eV
2) 13.6 eV2) 13.6 eV
3) hundreds of eV3) hundreds of eV
4) millions of eV4) millions of eV
5) billions of eV5) billions of eV
ConcepTest 30.5 ConcepTest 30.5 Radioactive Decay EnergyRadioactive Decay Energy
Follow-up:Follow-up: What process could release a photon with billions of What process could release a photon with billions of eV?eV?
1) the 1) the 234234Th nucleusTh nucleus
2) the alpha particle2) the alpha particle
3) both the same3) both the same
A uranium nucleus 238U (initially
at rest) decays into a thorium
nucleus 234Th and an alpha
particle. Which one has the
greater momentum?
ConcepTest 30.6a ConcepTest 30.6a Alpha Decay IAlpha Decay I
By momentum conservation, they must
have the samesame magnitude of momentum
since the initial momentum was zeroinitial momentum was zero.
1) the 1) the 234234Th nucleusTh nucleus
2) the alpha particle2) the alpha particle
3) both the same3) both the same
A uranium nucleus 238U (initially
at rest) decays into a thorium
nucleus 234Th and an alpha
particle. Which one has the
greater momentum?
ConcepTest 30.6a ConcepTest 30.6a Alpha Decay IAlpha Decay I
Follow-up:Follow-up: In what directions are the two products emitted? In what directions are the two products emitted?
1) the 1) the 234234Th nucleusTh nucleus
2) the alpha particle2) the alpha particle
3) both the same3) both the same
ConcepTest 30.6b ConcepTest 30.6b Alpha Decay IIAlpha Decay II
A uranium nucleus 238U (initially
at rest) decays into a thorium
nucleus 234Th and an alpha
particle. Which one has the
greater velocity?
1) the 1) the 234234Th nucleusTh nucleus
2) the alpha particle2) the alpha particle
3) both the same3) both the same
The momentum is mv and is thethe samesame for
both, but the alpha particle has the smaller smaller
massmass, so it has the larger velocitylarger velocity.
ConcepTest 30.6b ConcepTest 30.6b Alpha Decay IIAlpha Decay II
A uranium nucleus 238U (initially
at rest) decays into a thorium
nucleus 234Th and an alpha
particle. Which one has the
greater velocity?
1) the 1) the 234234Th nucleusTh nucleus
2) the alpha particle2) the alpha particle
3) both the same3) both the same
ConcepTest 30.6c ConcepTest 30.6c Alpha Decay IIIAlpha Decay III
A uranium nucleus 238U (initially
at rest) decays into a thorium
nucleus 234Th and an alpha
particle. Which one has the
greater kinetic energy?
1) the 1) the 234234Th nucleusTh nucleus
2) the alpha particle2) the alpha particle
3) both the same3) both the same
The kinetic energy 1/2 mv2 can be written as
KE = p2/2m. The momentum is themomentum is the samesame for
both, but the alpha particle has the smaller smaller
massmass, so it has the larger KElarger KE.
ConcepTest 30.6c ConcepTest 30.6c Alpha Decay IIIAlpha Decay III
A uranium nucleus 238U (initially
at rest) decays into a thorium
nucleus 234Th and an alpha
particle. Which one has the
greater kinetic energy?
What element results when
14C undergoes beta decay?
1) 1) 15C
2) 2) 15N
3) 3) 14C
4) 14N
5) 15O
ConcepTest 30.7 ConcepTest 30.7 Beta DecayBeta Decay
The reaction is: neutrinoeNC 14
7
14
6
What element results when
14C undergoes beta decay?
1) 1) 15C
2) 2) 15N
3) 3) 14C
4) 14N
5) 15O
Inside the nucleus, the reaction n n p + e p + e-- + + has
occurred, changing a neutron into a protonchanging a neutron into a proton, so the
atomic number Z increases by 1Z increases by 1. However the mass
number (A = 14) stays the same.
ConcepTest 30.7 ConcepTest 30.7 Beta DecayBeta Decay
Follow-up:Follow-up: How would you turn How would you turn 1414C into C into 1515N?N?
You have 16 kg of a radioactive
sample with a certain half-life
of 30 years. How much is left
after 90 years?
(1) (1) 8 kg8 kg
(2) (2) 4 kg4 kg
(3) (3) 2 kg2 kg
(4) (4) 1 kg1 kg
(5) (5) nothingnothing
ConcepTest 30.8a ConcepTest 30.8a Radioactive Decay Law IRadioactive Decay Law I
The total time (90 years90 years) is 3 half-lives3 half-lives.
After one half-life 8 kg left. After
two half-lives 4 kg left. After After
three half-lives three half-lives 2 kg left 2 kg left.
You have 16 kg of a radioactive
sample with a certain half-life
of 30 years. How much is left
after 90 years?
(1) (1) 8 kg8 kg
(2) (2) 4 kg4 kg
(3) (3) 2 kg2 kg
(4) (4) 1 kg1 kg
(5) (5) nothingnothing
ConcepTest 30.8a ConcepTest 30.8a Radioactive Decay Law IRadioactive Decay Law I
Follow-up:Follow-up: When will the sample be reduced to nothing? When will the sample be reduced to nothing?
You have 12 kg of a radioactive
substance. Ten years later, you
find that you only have 3 kg left.
Find the half-life of the material.
(1) (1) 20 years20 years
(2) (2) 10 years10 years
(3) (3) 7.5 years7.5 years
(4) (4) 5 years 5 years
(5) (5) 2.5 years2.5 years
ConcepTest 30.8b ConcepTest 30.8b Radioactive Decay Law IIRadioactive Decay Law II
After one half-life 6 kg left.
After two half-lives 3 kg left.
So if the total time is 10 yearstotal time is 10 years,
then the half-life must be 5 yearshalf-life must be 5 years.
(2 half-lives = 10 years)
You have 12 kg of a radioactive
substance. Ten years later, you
find that you only have 3 kg left.
Find the half-life of the material.
(1) (1) 20 years20 years
(2) (2) 10 years10 years
(3) (3) 7.5 years7.5 years
(4) (4) 5 years 5 years
(5) (5) 2.5 years2.5 years
ConcepTest 30.8b ConcepTest 30.8b Radioactive Decay Law IIRadioactive Decay Law II
Follow-up:Follow-up: How much of the sample is left after another 10 years? How much of the sample is left after another 10 years?
You have 400 g of a radioactive
sample with a half-life of 20 years.
How much is left after 50 years?
1) more than 100 g1) more than 100 g
2) 75 - 100 g2) 75 - 100 g
3) 75 g3) 75 g
4) 50 - 75 g4) 50 - 75 g
5) less than 50 g5) less than 50 g
ConcepTest 30.8c ConcepTest 30.8c Radioactive Decay Law IIIRadioactive Decay Law III
You have 400 g of a radioactive
sample with a half-life of 20 years.
How much is left after 50 years?
Total time (50 years) is 2Total time (50 years) is 2 1/2 1/2 half-lives. half-lives.
After one half-life 200 g left
After two half-lives 100 g left.
After three half-lives 50 g left.
So after 2So after 2 1/2 1/2 half-lives half-lives 75 g left ? 75 g left ?
No!!No!! Exponential function is not linear!
70.7 g 70.7 g leftleft NN = = NNooee–(0.693 / –(0.693 / TT1/21/2))tt
1) more than 100 g1) more than 100 g
2) 75 - 100 g2) 75 - 100 g
3) 75 g3) 75 g
4) 50 - 75 g4) 50 - 75 g
5) less than 50 g5) less than 50 g
ConcepTest 30.8c ConcepTest 30.8c Radioactive Decay Law IIIRadioactive Decay Law III
You have two samples, A (T1/2 = 10 yr) and B
(T1/2 = 20 yr) with initially different amounts.
The initial amount of sample A is 64 kg, while
the amount of sample B is unknown. If you
observe that the 2 amounts are equal after 40
years, what is the initial amount of B?
1) 64 kg1) 64 kg
2) 32 kg2) 32 kg
3) 16 kg3) 16 kg
4) 8 kg4) 8 kg
5) 4 kg5) 4 kg
ConcepTest 30.8d ConcepTest 30.8d Radioactive Decay Law IVRadioactive Decay Law IV
For sample A, after 40 years (4 half-lives4 half-lives), there is 4 kg4 kg left.
Now work backwards from there, for sample B:
40 years is 2 half-lives2 half-lives, so sample B initially had 16 kg16 kg.
You have two samples, A (T1/2 = 10 yr) and B
(T1/2 = 20 yr) with initially different amounts.
The initial amount of sample A is 64 kg, while
the amount of sample B is unknown. If you
observe that the 2 amounts are equal after 40
years, what is the initial amount of B?
1) 64 kg1) 64 kg
2) 32 kg2) 32 kg
3) 16 kg3) 16 kg
4) 8 kg4) 8 kg
5) 4 kg5) 4 kg
ConcepTest 30.8d ConcepTest 30.8d Radioactive Decay Law IVRadioactive Decay Law IV
Follow-up:Follow-up: When will the samples again have equal amounts? When will the samples again have equal amounts?
You have 10 kg each of a radioactive
sample A with a half-life of 100 years,
and another sample B with a half-life
of 1000 years. Which sample has the
higher activity?
1) sample A1) sample A
2) sample B2) sample B
3) both the same3) both the same
4) impossible to tell 4) impossible to tell
ConcepTest 30.9a ConcepTest 30.9a Activity and Half-Life IActivity and Half-Life I
If a sample has a shorter half-lifeshorter half-life, this means that
it decays more quicklydecays more quickly (larger decay constant )
and therefore has a higher activityhigher activity:
In this case, that is sample A.that is sample A.
You have 10 kg each of a radioactive
sample A with a half-life of 100 years,
and another sample B with a half-life
of 1000 years. Which sample has the
higher activity?
1) sample A1) sample A
2) sample B2) sample B
3) both the same3) both the same
4) impossible to tell 4) impossible to tell
ConcepTest 30.9a ConcepTest 30.9a Activity and Half-Life IActivity and Half-Life I
NN//tt = – = – NN
Follow-up:Follow-up: What is the ratio of activities for the two samples? What is the ratio of activities for the two samples?
The The same amountsame amount of two of two different radioactive samples different radioactive samples AA and and BB is prepared. If the is prepared. If the initial activity of initial activity of sample Asample A is is 5 5 timestimes largerlarger than that of than that of sample Bsample B, how do their half-, how do their half-lives compare?lives compare?
1) 1) TT1/21/2 of A is 5 times larger than B of A is 5 times larger than B
2) half-lives are the same2) half-lives are the same
3) 3) TT1/21/2 of A is 5 times smaller than B of A is 5 times smaller than B
ConcepTest 30.9b ConcepTest 30.9b Activity and Half-Life IIActivity and Half-Life II
A larger activitylarger activity means that a sample decays more decays more
quicklyquickly, and this implies a shorter half-lifeshorter half-life.
The The same amountsame amount of two of two different radioactive samples different radioactive samples AA and and BB is prepared. If the is prepared. If the initial activity of initial activity of sample Asample A is is 5 5 timestimes largerlarger than that of than that of sample Bsample B, how do their half-, how do their half-lives compare?lives compare?
1) 1) TT1/21/2 of A is 5 times larger than B of A is 5 times larger than B
2) half-lives are the same2) half-lives are the same
3) 3) TT1/21/2 of A is 5 times smaller than B of A is 5 times smaller than B
ConcepTest 30.9b ConcepTest 30.9b Activity and Half-Life IIActivity and Half-Life II
What is the Q-value
for radioactive decay
reactions?
1) 1) QQ < 0 < 0
2) 2) QQ > 0 > 0
3) 3) QQ = 0 = 0
4) sign of 4) sign of QQ depends on the nucleus depends on the nucleus
ConcepTest 31.1 ConcepTest 31.1 Nuclear ReactionsNuclear Reactions
Radioactive decay happens spontaneouslyspontaneously,
because the nucleus can reach a lower energy
state. Thus, such reactions can only occur
spontaneously if they releaserelease energyenergy
(exothermicexothermic ), so the QQ-value is positive-value is positive.
What is the Q-value
for radioactive decay
reactions?
1) 1) QQ < 0 < 0
2) 2) QQ > 0 > 0
3) 3) QQ = 0 = 0
4) sign of 4) sign of QQ depends on the nucleus depends on the nucleus
ConcepTest 31.1 ConcepTest 31.1 Nuclear ReactionsNuclear Reactions
Follow-up:Follow-up: Is radioactive decay an endothermic or exothermic reaction? Is radioactive decay an endothermic or exothermic reaction?
ConcepTest 31.2 ConcepTest 31.2 Nuclear Reaction ProductsNuclear Reaction Products
What is the nucleus that results
in the reaction given below?
n O H 8
16
1
2?
O17
8
O15
7
N15
7
F15
7
1) 1)
2) 2)
3) 3)
4) 4)
XXAA
ZZ
Add up the totals for nucleons (A) and
protons (Z) separately, and see what you
need to balance both sides:
Nucleons: 1 + 16 = Nucleons: 1 + 16 = xx + 2 + 2 xx = 15 = 15
Protons: 0 + 8 = Protons: 0 + 8 = yy + 1 + 1 yy = 7 = 7
The missing nucleus has The missing nucleus has AA = 15 and = 15 and ZZ = 7. = 7.
ConcepTest 31.2 ConcepTest 31.2 Nuclear Reaction ProductsNuclear Reaction Products
What is the nucleus that results
in the reaction given below?
n O H 8
16
1
2?
O17
8
O15
7
N15
7
F15
7
1) 1)
2) 2)
3) 3)
4) 4)
XXAA
ZZ
Follow-up:Follow-up: What would you get if you started with What would you get if you started with pp + + 1616OO instead? instead?
What element results when
14C undergoes beta decay?
1) 1) 15C
2) 2) 15N
3) 3) 14C
4) 14N
5) 15O
ConcepTest 31.3 ConcepTest 31.3 Beta Decay ProductsBeta Decay Products
XXAA
ZZ
The reaction is:
Essentially, a neutron turns into a proton (emitting a – particle), so the atomic number Z of the nucleus must increase by one unit, but without changing the atomic mass A.
neutrinoeNC 14
7
14
6
What element results when
14C undergoes beta decay?
1) 1) 15C
2) 2) 15N
3) 3) 14C
4) 14N
5) 15O
ConcepTest 31.3 ConcepTest 31.3 Beta Decay ProductsBeta Decay Products
XXAA
ZZ
How does the total mass
of the fission fragments
compare to the mass of
the original nucleus in a
fission reaction?
1) fission fragments have more mass 1) fission fragments have more mass
2) fission fragments have less mass 2) fission fragments have less mass
3) fission fragments have the same mass 3) fission fragments have the same mass
ConcepTest 31.4 ConcepTest 31.4 Nuclear FissionNuclear Fission
The fission reaction releases energyfission reaction releases energy, so the total energy (or mass) of the fission fragments must be lessmust be less than the energy (or mass) of the original nucleus.
How does the total mass
of the fission fragments
compare to the mass of
the original nucleus in a
fission reaction?
1) fission fragments have more mass 1) fission fragments have more mass
2) fission fragments have less mass 2) fission fragments have less mass
3) fission fragments have the same mass 3) fission fragments have the same mass
ConcepTest 31.4 ConcepTest 31.4 Nuclear FissionNuclear Fission
Follow-up:Follow-up: Where are the fission fragments Where are the fission fragments located relative to the original nucleus on located relative to the original nucleus on the curve of binding energy per nucleon?the curve of binding energy per nucleon?
How does the binding
energy per nucleon of a
fusion product compare
to that of the pieces that
combined to form it?
1) product has greater BE than the pieces 1) product has greater BE than the pieces
2) product has less BE than the pieces 2) product has less BE than the pieces
3) product has the same BE than the 3) product has the same BE than the
pieces pieces
ConcepTest 31.5 ConcepTest 31.5 Nuclear FusionNuclear Fusion
The fusion reaction releases energyfusion reaction releases energy, so the product is more tightly boundproduct is more tightly bound (more stable) than the separate pieces that combined to form it. This means that the binding energy binding energy per nucleon is greater for the fusion per nucleon is greater for the fusion productproduct.
How does the binding
energy per nucleon of a
fusion product compare
to that of the pieces that
combined to form it?
1) product has greater BE than the pieces 1) product has greater BE than the pieces
2) product has less BE than the pieces 2) product has less BE than the pieces
3) product has the same BE than the 3) product has the same BE than the
pieces pieces
ConcepTest 31.5 ConcepTest 31.5 Nuclear FusionNuclear Fusion
Follow-up:Follow-up: Which weighs more: Which weighs more: the fusion product or the pieces?the fusion product or the pieces?
Which type of radiation goes
farther in matter before
losing all of its energy ?
1) alpha radiation
2) beta radiation
3) gamma radiation
4) all about the same distance
ConcepTest 31.6 ConcepTest 31.6 Radiation ShieldingRadiation Shielding
paper aluminum lead
Alpha particles have such a large
charge, they ionize many atoms in
a short distance, and so lose their
energy rapidly and stop. Gamma
rays travel great distances before
ionizing an atom.
Which type of radiation goes
farther in matter before
losing all of its energy ?
1) alpha radiation
2) beta radiation
3) gamma radiation
4) all about the same distance
ConcepTest 31.6 ConcepTest 31.6 Radiation ShieldingRadiation Shielding
Curly is twice as far from a small
radioactive source as Moe.
Compared to Curly’s position,
the intensity of the radiation
(and therefore exposure) at
Moe’s position is about:
1) one-quarter
2) one-half
3) the same
4) double
5) quadruple
CurlyMoeradioactive source
ConcepTest 31.7a ConcepTest 31.7a Radiation Exposure IRadiation Exposure I
A small source can be treated as a point source and so it
obeys the inverse square lawobeys the inverse square law of intensity. Twice as close Twice as close
means 4 times the intensitymeans 4 times the intensity (and therefore exposure).
Curly is twice as far from a small
radioactive source as Moe.
Compared to Curly’s position,
the intensity of the radiation
(and therefore exposure) at
Moe’s position is about:
1) one-quarter
2) one-half
3) the same
4) double
5) quadruple
CurlyMoeradioactive source
ConcepTest 31.7a ConcepTest 31.7a Radiation Exposure IRadiation Exposure I
Curly is working 5 m from a highly
radioactive source and must reduce
his exposure by at least a factor of 10.
Assuming that an inverse square law
(1/r2) applies in this case, to what
distance should he move?
1) 7.5 m
2) 10 m
3) 15 m
4) 20 m
5) 50 m
Curly
radioactive source
ConcepTest 31.7b ConcepTest 31.7b Radiation Exposure IIRadiation Exposure II
A small source can be treated like a point source and so it
obeys the inverse square lawobeys the inverse square law of intensity. Moving to 15 m15 m
(3 times farther) only reduces the exposure by 9 timesreduces the exposure by 9 times. He
has to move farther away (20 m20 m) in order to get a factor of factor of
16 reduction16 reduction, which meets the “safety limit” of 10 times.
Curly is working 5 m from a highly
radioactive source and must reduce
his exposure by at least a factor of 10.
Assuming that an inverse square law
(1/r2) applies in this case, to what
distance should he move?
1) 7.5 m
2) 10 m
3) 15 m
4) 20 m
5) 50 m
Curly
radioactive source
ConcepTest 31.7b ConcepTest 31.7b Radiation Exposure IIRadiation Exposure II
Radiation can damage
matter such as metals
or biological tissue by:
1) heating up the material
2) causing cancer in the metal
3) producing fission reactions in the material
4) removing electrons from the atoms
5) producing fusion reactions in the material
ConcepTest 31.8 ConcepTest 31.8 Radiation DamageRadiation Damage
Radiation can ionize the atoms in
matter, which means knocking out
electrons. Metals become brittle
and cell processes can be disrupted.
Radiation can damage
matter such as metals
or biological tissue by:
1) heating up the material
2) causing cancer in the metal
3) producing fission reactions in the material
4) removing electrons from the atoms
5) producing fusion reactions in the material
ConcepTest 31.8 ConcepTest 31.8 Radiation DamageRadiation Damage
Follow-up:Follow-up: What type of radiation will tend to do the most damage? What type of radiation will tend to do the most damage?