Unit Test 10

1、单选题：
‍A positive charge is moving close to a spherical surface in space. The magnetic flux through the spherical surface is ‍
选项：
A: positive.
B: negative.
C: zero.
D:  variable.
答案: 【 zero.】

2、单选题：

​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?

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‍选项：
A: x-axis.
B: y-axis.
C: z-axis.
D: None of the above.
答案: 【 x-axis.】

3、单选题：

‏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           .

‌选项：
A:
B:
C:
D:
答案: 【 】

4、单选题：

‎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?

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‍选项：
A: A
B: B
C: C
D: D
答案: 【 C】

5、单选题：

‎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. 

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​选项：
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、单选题：

‎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 (  ).

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​选项：
A: abI/2
B: abIB/2
C: 0
D: abB/2
答案: 【 abIB/2】

7、单选题：
‌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 (  ).‎
选项：
A:
B: 0
C:
D: indeterminable
答案: 【 】

8、单选题：

​What is the net force on a magnetic dipole in a uniform magnetic field ?

‍选项：
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、单选题：

‏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 (  ).

‌选项：
A:
B:
C:
D:
答案: 【 】

10、填空题：

‏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           . 

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‎答案: 【 IRB##%_YZPRLFH_%##RIB##%_YZPRLFH_%##IBR##%_YZPRLFH_%##RBI##%_YZPRLFH_%##BIR##%_YZPRLFH_%##BRI】

11、填空题：

​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、填空题：
‏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、填空题：
‎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: 【 U/dv##%_YZPRLFH_%##U/vd##%_YZPRLFH_%##U/(dv)##%_YZPRLFH_%##U/(vd)】

14、填空题：

‎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】

Unit Test 11

1、单选题：

‎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 (  ).

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‎选项：
A: 0
B:
C:
D:
答案: 【 】

2、单选题：

‌There are several currents in space.   denotes magnetic fiel