Đề thi học kì 2 môn Vật lý 2 năm 2018-2019 có đáp án - Trường Đại học Bách Khoa TP. Hồ Chí Minh (Final exam of Physics 2 - No.1)

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National University – Ho Chi Minh City
University of Technology
Department of Engineering Physics

FINAL EXAM OF PHYSICS A2
2018-2019
Closed book exam – Duration: 90 min

Student’s name:

No.

1

Student ID:

A) (L.O.1, L.O.2) MCQ ANSWER SHEET (4 pts):
Choose for each question only one correct answer and darken corresponding circle in the following answer sheet.

1
2
3
4
5

A
O
O
O
O

O

B
O
O
O
O
O

C
O
O
O
O
O

D
O 6
O 7
O 8
O 9
O 10

A
O
O
O
O
O

B
O
O
O
O
O

C
O
O
O
O
O

D
O
O
O
O
O

11
12
13
14
15

A
O
O

O
O
O

B
O
O
O
O
O

C
O
O
O
O
O

D
O
O
O
O
O

16
17
18
19
20

A
O
O
O
O
O

B
O
O
O
O
O

C
O
O
O
O
O

D
O
O
O
O
O

1. Einstein’s Postulates state that …

A. The laws of physics are the same in all inertial frames of reference.
B. The speed of light in vacuum is the same in all inertial frames of reference and is independent of the
motion of the source.
C. A particle can travel at the speed of light in vacuum.
D. Both A and B.
2. Planck assumed:
A. Energy can only be absorbed or released in tiny discrete packets, which are an integer multiple of a
quantum energy.
B. Quantum energy ε of an electromagnetic wave of wavelength λ is defined by the formula ε = hc / λ ,
where h is Plank constant and c is the speed of light in vacuum.
C. Both A and B.
D. None of these.
3. An alpha particle (m = 6.64 x10-27 kg) emitted in the radioactive decay of uranium-238 has an energy
of 4.20 MeV. What is its de Broglie wavelength?
A. 7.02 x10-15m
B. 5.67 x10-15m
C. 1.67 x10-15m
D. 7.20 x10-15m
4. An electron in an atom initially has an energy of -3.2 eV above the ground state energy. It drops to a
state with an energy of -5.5 eV above the ground state energy and emits a photon in the process. The
momentum of the photon is:
A. 1.2 x 10-27 kg.m/s
B. 1.7 x 10-27 kg.m/s
C. 4.3 x 10-27 kg.m/s
D. 2.3 x 10-27 kg.m/s
5. There are Uranium and Lead atoms in Uranium ore. Lead atoms are the products of the radiation of
Uranium. The half life of Uranium is 5.5×109 years. How old is the ore if the ratio between the number
of Uranium and Lead atoms are 5:1:
A.1.45 x 109 years
B. 4.47 x 109 years

6.02 x 108 years
8.02 x 1018 years
6. Einstein suggested that:
A. Light is composed of tiny particles called protons.
B. The speed of photon is c = 3.108 m/s in free space and equal v = c/n in medium
C. Each photon has energy ε = hc / λ , where h: Planck’s constant, λ : light wavelength
D. All of the above.
7. The wave function of a particle must satisfy certain feratures:
A. Must be a single-valued function.
B. Must be normalizable.
C. Must be a continuous function and the first derivative also must be continuous.


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D. All of the above.
8. In Compton effect, the maximum kinetic energy of the emitted electrons is 3 keV. What's the
wavelength of the incident light?
A. 0.3 Ǻ
B. 0.5 Ǻ
C. 0.6 Ǻ
D. 0.4 Ǻ
9. In hydrogen atom, electron is in the quantum state 2s, received any energy to get the excited state.
What is the proper wave function of the excited state?
A. ψ511
B. ψ400
C. ψ500
D. ψ401
10. The binding energy of a nucleus is the energy that must be supplied to:
A. bind nucleons together in nucleus
B. remove an alpha particle

C. remove a beta particle D. separate the nucleus into nucleons
11. The half-life of a radionuclide is 60 days. After how many days will it decay to 0.1% of its original
activity?
A. 300 B. 600 C. 3000 D. 6000
12. The formulas of non-relativistic microscopic particle momentum is:
A. p = h/λ
B. p = (2mE)1/2
C. A and B are correct D. A and B are wrong
(For 02 next questions) A hydrogen atom in the 5g state is placed in a magnetic field of 0.600 T that is in
the z-direction.
13. Into how many levels is this state split by the interaction of the atom’s orbital magnetic dipole
moment with the magnetic field?
A. 10
B. 9
C. 8
D. 7
14. What is the energy separation between adjacent levels?
A. 5,1.10-5eV
B. 3,47.10-5eV
C. 3,6.10-5eV

D. 2,6.10-5eV

15. Which of the following (n, l, ml, ms) combinations is possible for an electron in an atom?
A. 3, 3, 1, −1/2
B. 6, 2, 0, 1/2
C. 3, 2, 3, 1/2
D. 3, 1, −1, 1
16. The frequency and wavelength of the matter wave associated with a 10eV free electron are:
A. 1.5 × 1034 Hz, 3.9 × 10−10 m

B. 1.5 × 1034 Hz, 1.3 × 10−34 m
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−9
C. 2.4 × 10 Hz, 1.2 × 10 m
D. 2.4 × 1015 Hz, 3.9 × 10−10 m
17. Which of following statements is wrong :
A. ∆m = 0,±1 B. ∆l = ±1
C. ∆j = ±1
D. A and B are correct
(For 02 next questions) Two stars, both of which behave like ideal blackbodies, radiate the same total
energy per second. The cooler one has a surface temperature T and a diameter 3.0 times that of the hotter
star.
18. What is the temperature of the hotter star in terms of T?
A. 4T
B. 1.7T C. 2.04T D. 2T
19. What is the ratio of the peak-intensity wavelength of the hot star to the peak-intensity wavelength of
the cool star?
A. 0.4
B. 0.58
C. 4.04 D. 0.2
20. A radionuclide decays to a nuclide with the same A, and with Z increasing by 1. This is an example
of ……… decay.
A. Beta minus
B. Beta plus
C. Gamma
D. Alpha


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B. PROBLEMS (L.O.1, L.O.2):
1. (2 pts) A black-body emits the radiation with the greatest intensity wavelength 0.550 μm. Calculate:
a) The temperature of the body.
b) The energy radiated per second from 10cm2 of the body surface.
Sol.
T :=b/.76e-6= 5269K
E := s*T^4*10e-4= 218522J
2. (2 pts) Electron in the Hydrogen has maximal angle between
cos α max = −3 / 2 3 .
a) What is the orbital quantum number l of mentioned electron state.
b) Find the possible values of L and Lz for this electron?
Sol.
l = 3; L = 2 3; Lz = 0, ±1, ±2, ±3

and the z-axis with

3. (1 pt) a) Calculate the minimum energy required to separate a tritium (3H) into its component parts
(1amu= 931.2 MeV), where mproton = 1.00727 amu, mneutron = 1.00866 amu, mtritium = 3.0161 amu.
b) Why should the fusion occur in the condition of very high temperature (~106 K) ?
Sol.
E= 7.9 MeV = 0.126e-11 J
4. (1 pt) A particle moving in one dimension (the x-axis) is described by the wave function
 Ae − bx , x ≥ 0
ψ (x) =  bx
 Ae , x < 0
where b = 2.00 m-1, A>0, and the +x-axis points toward the right.
a) Determine A so that the wave function is normalized.
b) Find the probability of finding this particle in each of the following regions: (i) within 50.0 cm of the
origin, (ii) on the left side of the origin, (iii) between x = 0.500 m and x = 1.00 m.
Sol.

A = sqrt(b) = sqrt(2) m-1
Some useful constants:
h = 6,625.10 −34 J .s
c = 3.10 8 m / s

σ = 5,67.10 −8 Wm −2 K −4
me = 9,1.10 −31 kg

b = 2,898.10 −3 mK
e = 1,6.10 −19 C