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16 Magnetic Field and Magnetic Forces Unit Test 10
1、 A positive charge is moving close to a spherical surface in space. The magnetic flux through the spherical surface is
A:positive.
B:negative.
C:zero.
D: variable.
答案: zero.
2、 A planar rectangular coil of dimensions 
is oriented perpendicular to a uniform magnetic field. A current is suddenly started in the coil. About which axis will the coil begin to rotate?
A:x-axis.
B:y-axis.
C:z-axis.
D:None of the above.
答案: x-axis.
3、 A particle with speed v, charge q, and mass m enters a uniform magnetic field at the angle 
with the direction of magnetic field 
. The period of motion in a helical path is .
A:
B:
C:
D:
答案:
4、 A current-carrying circular loop in a uniform magnetic field is placed in four different orientations as shown in Figures A, B, C and D. Which figure depicts a stable equilibrium configuration?
A:A
B:B
C:C
D:D
答案: C
5、 As figure shown, a current-carrying strip of metal lies in a uniform magnetic field pointing inward. The Hall voltage between opposite edges A and A′appears. 
A:The potential level of A is higher than that of A′
B:The potential of A is lower than that of A′.
C:The potential of A is equal to that of A′.
D:Not enough information given.
答案: The potential of A is lower than that of A′.
6、 The right-angled triangular loop of wire shown in Figure carries a current I. The loop is in a uniform magnetic field that has magnitude B and the same direction as the current in side PQ. The magnitude of the torque on the loop is ( ).
A:abI/2
B:abIB/2
C:0
D:abB/2
答案: abIB/2
7、 A square current loop with length a on each side carries a current I. The loop is in a uniform magnetic field B. If the loop is in the stable equilibrium, the magnetic flux passing through the loop onlyby the uniform field is ( ).
A:
B:0
C:
D:indeterminable
答案:
8、 What is the net force on a magnetic dipole in a uniform magnetic field 
?
A:Nonzero and in the direction of .
B:Nonzero and in the direction of 
.
C:Nonzero and perpendicular to .
D:zero.
答案: zero.
9、 A straight horizontal copper rod with mass m per unit length carries a current I from west to east in a horizontal uniform magnetic field 
toward the northeast, as shown in Figure. The magnitude of the magnetic field that can hold up the copper rod per unit length is ( ).
A:
B:
C:
D:
答案:
10、 A long wire carrying current I has a quarter-circular segment of radius R and is placed in a uniform magnetic field B as shown in the figure. The magnetic field is confined to a limited region of space. The horizontal component of the force that the magnetic field exerts on the wire MN is . 
答案: (以下答案任选其一都对)IRB;
RIB;
IBR;
RBI;
BIR;
BRI
11、 Electric field 
and magnetic field 
are perpendicular to the particle’s velocity and to each other as shown in the figure. What is the speed that the particles must have when they leave the source for them to be able to pass through the very narrow and long field region? . (In form of / , if fraction)
答案: E/B
12、 A current-carrying circular loop (area A and current I ) is placed in a uniform magnetic field B. The magnetic torque is when the loop is in a stable equilibrium state.
答案: 0
13、 An electron travels with speed v between two parallel charged plates of separation d and potential difference U as shown in Figure. The magnitude of the magnetic field that will allow the electron to pass between the plates without being deflected equals . (In form of / )
答案: (以下答案任选其一都对)U/dv;
U/vd;
U/(dv);
U/(vd)
14、 A circular loop with radius R carries a current I. The loop is in a uniform field 
. If the magnetic flux passing through the loop is maximum, the torque on the loop is .
答案: 0
17 Sources of Magnetic Field Unit Test 11
1、 In vacuum a current I flows through the wire which is bent into a semicircular section and two long straight sections. Magnetic field 
at point O equals ( ).
A:0
B:
C:
D:
答案:
2、 There are several currents in space. denotes magnetic field at any point and 
denotes the line integral of around a closed path L. According to Ampere’s law,
A: 
is determined by the currents enclosed by the loop L and the shape of the loop L.
B:
is determined by all currents.
C: is determined by all ocurrents.
D: is determined by the currents enclosed by the loop L.
答案: is determined by all ocurrents.
3、 A charge －q is moving at a constant speed of v in the +y-direction relative to an inertial reference frame. At an instant when the point charge is at the origin, the magnetic-field vector it produces at point (a,0,0) is ( ).
A:
B:
C:
D:
答案:
4、 An electron and a proton are moving at speed 
and 
respectively in perpendicular paths. At the instant when they are at the positions shown in Figure, the magnitude of the magnetic force that the electron exerts on the proton is ( ).
A:0
B:
C:
D:
答案: 0
5、 A long wire with current I has two straight segments and a circular segment with radius R as shown in Figure. The magnitude of the magnetic field at the center of the circle is ( ).
A:
B:
C:
D:
答案:
6、 The current distribution is shown in Figure. The value of the line integral of around the closed path L is ( ). (The permeability of vacuum is given by 
.) 
A:
B:
C:
D:
答案:
7、 Two wires are bent into semicircles of radius a as shown in Figure. The resistance of the upper half is R and that of the lower half is 3R . The magnetic field at the center of the circle is ( ).
A:
B:
C:
D:
答案:
8、 The figure shows, in cross section, that five current-carrying wires pass through the plane of the figure. The currents are respectively 
with their directions indicated in the figure. The line integral for closed path equals .
A:
B:
C:
D:
答案:
9、 A pair of point charges q and Q are moving and at the location as shown in Figure with speed v and V respectively. What is the magnetic forces f that Q exerts on q and F that q exerts on Q ?
A:
B:
C:
D:
答案:
10、 Which of the following materials are attracted to a magnet?
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