SKKU-CS-009
기초자연과학영역(BSM) 공동시험문제
Basic Science and Mathematics Common Examination
학기
Semester
학과/계열
Dept./Division
과목명
Subject
수업정보
Class Time
유의사항
Note
2015 년
2 학기
일반물리학2
요일
Day
시간
Time
시험구분
Exam Type
중간 Mid Term
기말 Final
학번
Student PIN
학수번호
Course Code
수업담당교수
Instructor
☑
☐
시험시간
Exam Time
60 분/Minutes
성명
Name
분반
Section Number
감독자확인
Proctor’s Signature
GEDB010
1. Electronic calculator is not allowed!!
2. Answer the questions in English or Korean.
1. [25 points] Properties of a metallic sphere:
2. [25 points] An electron is placed under a uniform magnetic
(a) (10 pts) How does a piece of metal respond to an external field of 0.01 T pointing to the positive x-axis. The electron has
electric field and why? Describe the answer in words. You do an initial velocity of 3×106 i + 4×106 j m/s and is initially
not need to use equations.
located at the origin. The mass and charge of the electron are
9×10-31 kg and –1.6×10-19 C, respectively.
You are given a charge-neutral, metallic
(a) (5 pts) Describe the motion of the electron.
solid sphere of radius . Suddenly, by
(b) (5 pts) Describe the motion of the electron when the magnetic
magic, a charge   (>0) appears at the
field is reversed.
center of the sphere.
(c) (5 pts) Find the period of the electron motion.
(b) (10 pts) Describe the response of the
(d) (5 pts) What is the speed of the electron at  = 10 s?
metallic sphere to this sudden change.
(e) (5 pts) If an additional electric field of 2.8125×10-6 V/m is
Note that the positive charge (  )
applied pointing to the negative x-direction from the beginning,
remains at the center all the time.
what will be the speed of the electron at  = 10 s?
(c) (5 pts) After reaching a new
Answers:
equilibrium, make a rough sketch of the induced charge density (a)) (5 pts) A helical motion: Along the x-axis, it is a constant
 and the radial electric field   as a function of the
velocity motion. Within the yz-plane, it is a counterclockwise
distance  from the center of the sphere.
circular motion.
Answers:
(b)) (5 pts) A helical motion: Along the x-axis, it is a constant
(a) (10 pts) A metal responds to electric field by generating a velocity motion (no change). Within the yz-plane, it is now a
current in the direction of the field according to Ohm’s law. The clockwise circular motion.
current flow continues until the new charge distribution creates (c)) (5 pts)           






an electric field that precisely cancels the external field, for a net
electric field of zero inside the metal in the new equilibrium.
(b) (10 pts) The sudden appearance of charge +Q will generate a
radial electric field of a single, isolated charge. Electric current (d))
will flow radially, resulting in the accumulation of positive net (e))
charge +Q at the surface of the sphere and the charge –Q
which surround the inserted charge. In effect, the inserted charge
+Q is surrounded by a cloud of opposite charge distributed over
a certain distance. Beyond this distance the net charge becomes
zero and the metallic interior will experience zero net electric
field.
(c) (5 pts) The electric charge density and field distributions are
roughly given by


 ×  
  ×  
     


 ×  
(5 pts)  
  

  ×  
  ×   ×  

   ×
(5 pts)     

 ×  
    
  ×   ×     ×
  
    
 ×  
이 부분은 출제자 및 채점자를 위한 공간입니다. / Do not write your answer here: this is only for grading/marking.
문제번호
합계
1
2
3
4
5
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7
8
9
10
11
12
Problem No.
Total
점수
Score
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Copyright ⓒ 2014 College of Science, Sungkyunkwan University (SKKU)
SKKU-CS-009
3. [25 points] In the circuit shown in the Figure below, the
switch S has been opened for a long time. Then it is suddenly
closed.
(a) (7 pts) Determine the time constant  before the switch is
closed.
(b) (8 pts) Determine the time constant  after the switch is
closed.
(c) (10 pts) When the switch be closed at   , determine the
current in the switch as a function of time .
Answers:
(a) (7 pts)      
(b) (8 pts)    
(c) (10 pts)
4. [25 points] Force on a semicircular
conductor:
A
wire
bent
into
a
semicircle of radius  forms a closed
circuit and carries a current  . The
wire lies in the xy plane, and a
uniform magnetic field is directed
along the positive y axis as shown in
the Figure right.
(a) (10 pts) Find the magnitude and
direction of the magnetic force acting on the curved portion.
The Magnetic field created by a long current-carrying wire: A
long, straight wire of radius  carries
a steady current  that is uniformly
distributed through the cross section
of the wire (refer to the Figure
right).
(b) (10 pts) Calculate the magnetic
field a distance  from the center of
the wire in the regions (i)  ≥  and
(ii)   .
(c) (5 pts) Draw the graph of the magnitude of the magnetic field
as a function of a distance  from the center of the wire in
both regions  ≥  and   .
Answers:
(a) (10 pts)
(b) (10 pts)
* Note that the total current passing through the plane of the
circle is I and apply Ampere’s law: Solve for B:
Solve for B:
*Now consider the interior of the wire, where r < R. Here the
current I’ passing through the plane of circle 2 is less than
the total current I. Set the ratio of the current I’ enclosed
by circle 2 to the entire current I equal to the ratio of the
area   enclosed by circle 2 to the cross-sectional area  
of the
wire:
Solve for I’:
* Apply Ampere’s law to circle 2:
Solve for B:
(c) (5 pts)
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Copyright ⓒ 2014 College of Science, Sungkyunkwan University (SKKU)