Physics 11: Subatomic Mass, Energy & Momentum
A. Atomic Nucleus
1. There are 82 protons in a lead nucleus. Why doesn't the lead
nucleus burst apart?
(A) electric repulsive forces don't exist in the nucleus
(B) gravity overpowers the electric repulsion
(C) neutrons neutralize the positively charged protons
(D) none of the above
2. What weighs more, A—an electron and a proton, or B—a
hydrogen atom?
(A) A
(B) B
(C) tie
Questions 3-5 radiation passes through a vacuum, where one
side is positively charged and the other is negatively
charged.
++++++++++++++++++++
A
B
______________ C
3. Which is the path of an alpha particle?
4. Which is the path of a beta particle?
5. Which is the path of gamma radiation?
Questions 6-9 Refer to the spontaneous nuclear decay:
238 U  234 Th + 4 He
92
90
2
6. Which weighs more, A—U-238, or B—Th-234 + He-4?
(A) A
(B) B
(C) tie
7. Which has greater momentum, A—Th-234, or B—He-4?
(A) A
(B) B
(C) tie
8. Which has greater velocity, A—Th-234, or B—He-4?
(A) A
(B) B
(C) tie
9. Which has greater kinetic energy, A—Th-234, or B—He-4?
(A) A
(B) B
(C) tie
10. What is produced by the beta decay of 31H?
(A) 21H
(B) 11H
(C) 32He
(D) 42He
210
11. What is produced by the alpha decay of 84Po?
(A) 21082Pb (B) 20682Pb (C) 21086Rn (D) 21486Rn
12. Complete the nuclear equation: 146C + 0-1e  ___
(A) 156C
(B) 157N
(C) 145B
(D) 147N
13. Complete the nuclear equation: 10n + 168O  ___ + 21H
(A) 178O
(B) 158O
(C) 157N
(D) 159F
Questions 14-15 16 g of radioactive material has a 30-yr half-life.
14. How much is left after 90 years?
(A) 8 g
(B) 4 g
(C) 2 g
(D) 1 g
15. How long will it take to reduce the amount to 8 g?
(A) 30 yr
(B) 60 yr
(C) 90 yr
(D) 120 yr
16. What is the half life of a radioactive material that decays to ¼
the original amount in 16 years?
(A) 1 yr
(B) 2 yr
(C) 4 yr
(D) 8 yr
17. Which is more radioactive, substances A (t½ = 100 s) or B (t½
= 50 s)?
(A) A
(B) B
(C) tie
18. Which type of radiation goes farther in matter before losing
all of its energy?
(A) alpha
(B) beta
(C) gamma
19. Define
Name __________________________
21. Complete the following chart for the isotope, U-235.
Number of Number of Number of
Z value
A value
nucleons
protons
neutrons
22. Consider the helium nuclide (42He = 4.001504). Determine
a. the difference in mass between nucleons and nuclide.
(1) in u
(2) in kg
b.
the total binding energy in J.
c.
the binding energy per nucleon.
23. Complete the following chart.
Symbol
Mass
alpha
Charge
Penetrating ability
beta
gamma

24. Fill in the missing symbols.
10B
+ n  + ____
____ + n  + 2H
50Cr
+ n  + ____
25. Consider the alpha decay of U-238:

+ 234Th
238U = 238.050784 u 4He = 4.002602 u 234Th = 234.043601 u
a. Determine the change in mass per U-238 atom.
(1) in u
238U
4He
(2) in kg
b.
Is the reaction spontaneous?
c.
Determine the change in energy (in J) per atom.
26. A sample of 100Pd (half-life 4 days) has mass 1.776 g at 3:00
P.M. on July 4; what mass of 100Pd remains at 3:00 P.M. on
July 16?
27. Consider a helium-4 atom (atomic mass = 4.00 u).
a. What is the mass in kg?
nucleon
nuclide
b.
What is the energy equivalence in J?
Z#
A#
isotope
20. Consider a carbon-12 atom (a.m. = 12.0 u).
a. What is the mass in kg?
b.
What is the energy equivalence in J?
28. Complete the following chart for the isotope, Rn-226.
Number of Number of Number of
Z value
A value
nucleons
protons
neutrons
29. Determine the binding energy (in joules) of an average
nucleon in 3H (3.015500 u) by completing the following
sequence of calculations
m
(u)

BE
BE/A
30. Fill in the missing symbols.
27Al
+  ____ + 30P
9Be
+  n + ____
31. Stationary Radium-226 (225.97709 u) undergoes an alpha
decay (4.001504 u) to produce radon-222 (221.97036).
a. Write a nuclear equation for this radioactive decay.

b.
Calculate the change in mass in kg for this reaction.
c.
Calculate the energy is joules released per decay.
d.
If all the released energy becomes kinetic energy, what
is K/KRa?
e.
What is the alpha particle's velocity if 98 % of the energy
is absorbed by the particle?
f.
What is the De Broglie wavelength of the alpha particle?
32. How long does it take for a sample of
lose 7/8 of its activity?
32P
(t1/2 = 14 days) to
B. Photons and Electrons
33. Check which color has the greatest value for the following.
red
yellow
violet
can't tell
frequency
wavelength
energy
relativistic mass
momentum
intensity
34. Complete the chart for an X-ray photon ( = 1.54 x 10-10 m).
f 
E
m 
p
35. A proton and antiproton (m = 1.67 x 10-27 kg) collide and
convert all mass into photon energy. Determine the photon's
E 
f

p
36. What is the ionization energy of ground state hydrogen?
(A) 0 eV
(B) 13.6 eV (C) 41.2 eV (D) 54.4 eV
37. Which transition results in the greatest gain in energy?
(A) 2  5 (B) 5  2 (C) 3  10 (D) 1  2
38. The Balmer series includes two blue, a blue-green and red
spectral line. Which transition generates the red?
(A) 3  2 (B) 4  2 (C) 5  2 (D) 6  2
39. A hydrogen electron is excited to n = 4. How many different
transitions are possible to reach ground state?
(A) 1
(B) 2
(C) 3
(D) 6
Question 40-42 Metal A has a greater work function  compared
to metal B.
40. Which metal has the greater threshold wavelength?
(A) A
(B) B
(C) tie
41. Which metal has the greater threshold frequency?
(A) A
(B) B
(C) tie
42. Green light does NOT generate photoelectrons in metal A.
Which color might be able to generate photoelectrons?
(A) red
(B) orange (C) yellow (D) blue
Questions 43-44 A metal surface emits photoelectrons when
exposed to 400-nm light.
43. What happens if the metal is exposed to 300-nm light?
(A) more electrons are emitted
(B) fewer electrons are emitted
(C) more energetic electrons are emitted
(D) no electrons are emitted
44. What will happen if the metal is exposed to brighter 400-nm
light?
(A) more electrons are emitted
(B) fewer electrons are emitted
(C) more energetic electrons are emitted
(D) no electrons are emitted
45. The speed of proton A is faster than proton B. Which one has
the longer De Broglie wavelength?
(A) A
(B) B
(C) tie
46. A proton and electron have the same speed, which has the
longer De Broglie wavelength?
(A) proton
(B) electron
(C) tie
47. A proton and electron have the same momentum, which has
the longer De Broglie wavelength?
(A) proton
(B) electron
(C) tie
48. Complete the chart for a hydrogen transition from n = 2  3.
E2
E3
E
photon
49. The hypothetical atom has four energy states as shown.
a. Calculate the change in energy for all transitions from
the forth energy level to ground state.
Transition
E
n=4
-4
n=4n=3
n=3
-16
n=4n=2
Energy (eV)
m
(kg)
-36
n=2
n=4n=1
n=3n=2
n=3n=1
-144
b.
n=1
n=2n=1
Ground state atoms are irradiated with photons having
energies between 120 eV and 130 eV. What energies can
be emitted by atoms of this gas?
50. What is the threshold wavelength that will emit electrons from
a metal whose work function is 3.10 eV?
51. A metal surface ( = 2.40 eV) is exposed to 240 nm light.
a. What is the energy of the photons?
b.
What is the maximum kinetic energy (in eV) of electrons
ejected from a surface?
52. Kinetic energy (eV) of photoelectrons vs. frequency of
incident photons for sodium metal is graphed below.
a.
What is the wavelength of green light in nm?
b.
What is the maximum kinetic energy of photoelectrons
emitted when green light shines on sodium?
c.
What is the work function of the metal?
d.
What is the threshold frequency?
e.
What is the threshold wavelength in nm? (two methods)
f.
What is the energy of the photons? (two methods)
g.
Calculate h in J•s using the data from the graph.
53. Determine the following with a wavelength of 500 nm.
photon
electron

(m)
p
(kg•m/s)
m
(Kg)
v
(m/s)
f
(s-1)
E
(J)
E
(eV)
Practice Multiple Choice
Briefly explain why the answer is correct in the space provided.
1. The nuclear reaction X  Y + Z occurs spontaneously. If Mx,
My, and Mz are the masses of the three particles, which of the
following relationships is true?
(A) MX < MY – MZ
(B) MX < MY + MZ
(C) MX > MY + MZ
(D) MX – MY < MZ
2.
A negative beta particle is emitted during the radioactive
decay of 21482Pb. Which is the resulting nucleus?
(A) 21080Hg (B) 21481Tl (C) 21383Bi (D) 21483Bi
3.
The deuteron (21H) mass md is related to the neutron mass
mn and the proton mass mp by which of the following?
(A) md = mn + mp
(B) md = mn + mp + mBE
(C) md = 2(mp)
(D) md = mn + mp – mBE
4.
At noon the decay rate is 4,000 counts/minute. At 12:30
P.M. the decay rate is 2,000 counts/minute. The predicted
decay rate in counts/minute at 1:30 P.M. is
(A) 0
(B) 500
(C) 667
(D) 1,000
5.
In the photoelectric effect, the maximum speed of electrons
emitted by a metal surface when it is illuminated by light
depends on which of the following?
I. Intensity of the light
II. Frequency of the light
III. Nature of the photoelectric surface
(A) I only
(B) II only (C) III only (D) II and III only
6.
If photons of light of frequency f have momentum p, photons
of light of frequency 2f will have a momentum of
(A) 2p
(B) ½p
(C) p
(D) 4p
7.
Light of a particular wavelength is incident on a metal
surface, and electrons are emitted from the surface as a
result. To produce more electrons per unit time but with less
kinetic energy per electron, one should
(A) Increase the intensity and decrease the wavelength.
(B) Increase the intensity and the wavelength.
(C) Decrease the intensity and the wavelength.
(D) Decrease the intensity and increase the wavelength.
8.
If the momentum of an electron doubles, its de Broglie
wavelength is multiplied by a factor of
(A) ¼
(B) ½
(C) 1
(D) 2
Questions 9-10 The spectrum of visible light emitted during
transitions in excited hydrogen atoms is composed of blue,
green, red, and violet lines
9. What characteristic determines energy carried by a photon?
(A) amplitude
(B) phase
(C) frequency
(D) velocity
10. Which color is associated with the greatest energy change?
(A) blue
(B) red
(C) green (D) violet
Questions 11-13 Use the graphs to answer the questions.
(A)
(B)
(C)
(D)
11. Which graph shows the de Broglie wavelength of a particle
versus the linear momentum?
19. A photon having energy of 9.4 eV strikes a hydrogen atom in
the ground state. Why is the photon not absorbed by the
hydrogen atom?
(A) The atom's orbital electron is moving too fast
(B) The photon striking the atom is moving too fast.
(C) The photon's energy is too small.
(D) The photon is being repelled by electrostatic force.
20. Electrons with energy E have a de Broglie wavelength of
approximately . In order to obtain electrons whose de
Broglie wavelength is 2, what energy is required?
(A) ¼E
(B) ½E
(C) 2E
(D) 4E

12. Which graph shows the maximum kinetic energy of the
emitted electrons versus the frequency of the light?
Practice Free Response
1.
13. Which graph shows the total photoelectric current versus the
intensity of the light for a fixed frequency?
The fusion of a proton (11p = 1.007276 u) and neutron
(10n = 1.008665 u) produces deuterium, 21H (2.013553 u).
a. Write a nuclear equation.
b.
Calculate the change in mass in u.
c.
Calculate the change in mass in kg (1 u = 1.66 x 10-27 kg)
Questions 14-19 The diagram shows the energy levels for H2.

2.
d.
Calculate the energy in joules released.
e.
The deuterium absorbs all of the energy from part d as
kinetic energy. What is the speed of the deuterium atom?
The diagram shows the lowest four energy levels of an atom.
An electron in n = 4 state makes a transition to n = 2.
14. What is the energy, in eV, of a photon emitted by an electron
as it moves from the n = 6 to the n = 2?
(A) 0.38 eV (B) 3.02 eV (C) 3.40 eV (D) 13.60 eV
15. The energy of the photon (in J) is closest to
(A) 6.1 x 10-20 J
(B) 4.8 x 10-19 J
(C) 5.4 x 10-19 J
(D) 2.2 x 10-18 J
Determine
a. the energy of the emitted photon in eV.
b.
the wavelength of the emitted photon.
16. What is the frequency of the emitted photon?
(A) 9.2 x 1013 s-1
(B) 7.3 x 1014 s-1
14
-1
(C) 8.2 x 10 s
(D) 3.3 x 1015 s-1
c.
the momentum of the emitted photon.
17. What is the wavelength of the emitted photon?
(A) 4.1 x 10-7 m
(B) 3.3 x 10-7 m
(C) 5.4 x 10-7 m
(D) 5.0 x 10-7 m
The photon is incident on silver, which emits a photoelectron
(m = 9.11 x 10-31 kg) with wavelength  = 5.2 x 10-10 m.
d. What is the momentum of the photoelectron in kg•m/s?
18. What is the minimum amount of energy needed to ionized an
electron that is initially in the n = 6 energy level?
(A) 13.22 eV
(B) 5.12 eV
(C) 0.38 eV
(D) 0.16 eV
e.
What is the kinetic energy of the photoelectron in eV?
f.
What is the work function of silver?