conceptest 27.1photons 400 nm500 nm600 nm700 nm which has more energy, a photon of: 1) red light 2)...

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


400 nm 500 nm 600 nm 700 nm

energyenergylowlowhighhigh

EE = = hchc / /





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






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


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







Remember that cc = = ff and that E = h fE = h f

A metal surface is struck with A metal surface is struck with


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?






ConcepTest 27.2dConcepTest 27.2d Photoelectric Effect IVPhotoelectric Effect IV

A metal surface is struck with A metal surface is struck with


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?






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 = 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


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


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.








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?




ConcepTest 30.6b ConcepTest 30.6b Alpha Decay IIAlpha Decay II





greater velocity?




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





greater velocity?




ConcepTest 30.6c ConcepTest 30.6c Alpha Decay IIIAlpha Decay III





greater kinetic energy?




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





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



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.


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?


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


(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)


substance. Ten years later, you

find that you only have 3 kg left.

Find the half-life of the material.



(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


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


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?



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



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?

conceptest 27.1photons 400 nm500 nm600 nm700 nm which has more energy, a photon of: 1) red light 2)...

Documents

blue light

green light

nm yellow light

emitted electrons

metal b

metal surface

work function of w

greater work function