問題一覧
1
At one instant an electron is moving in the positive x direction along the x axis in a region where there is a uniform magnetic field in the positive z direction. When viewed from a point on the positive z axis, it subsequent motion is:
counterclockwise around a circle in the xy plane
2
An electron and a proton are both initially moving with the same speed and in the same direction at 90° to the same uniform magnetic field. They experience magnetic forces, which are initially:
equal in magnitude but opposite in direction
3
A cyclotron operates with a given magnetic field and at a given frequency. If R denotes the radius of the final orbit, the final particle energy is proportional to:
R^2
4
A loop of wire carrying a current of 2.0 A is in the shape of a right triangle with two equal sides, each 15 cm long. A 0.7T uniform magnetic field is parallel to the hypotenuse. The resultant magnetic force on the two equal sides has a magnitude of:
0
5
A loop of wire carrying a current of 2.0 A is in the shape of a right triangle with two equal sides, each 15 cm long. A 0.7 T uniform magnetic field is in the plane of the triangle and is perpendicular to the hypotenuse. The magnetic force on either of the two equal sides has a magnitude of:
0.15N
6
A current is clockwise around the outside edge of this page and a uniform magnetic field is directed parallel to the page, from left to right. If the magnetic force is the only force acting on the page, the page will turn so the right edge:
moves toward you
7
The units of magnetic dipole moment are:
ampere-meter^2
8
You are facing a loop of wire which carries a clockwise current of 3.0 A and which surrounds an area of 5.8 × 10-2 m?. The magnetic dipole moment of the loop is:
0.17A • m^2 away from you
9
The magnetic torque exerted on a flat current-carrying loop of wire by a uniform magnetic field B is:
maximum when the plane of the loop is parallel to B
10
A circular loop of wire with a radius of 20 cm lies in the xy plane and carries a current of 2 A, counterclockwise when viewed from a point on the positive z axis. Its magnetic dipole moment is:
0.25A • m^2 in the positive z direction
11
The magnetic dipole moment of a current-carrying loop of wire is in the positive z direction. If a uniform magnetic field is in the positive x direction the magnetic torque on the loop is:
in the positive y direction
12
For a loop of current-carrying wire in a uniform magnetic field the potential energy is a minimum if the magnetic dipole moment of the loop is:
in the same direction as the field
13
A loop of current-carrying wire has a magnetic dipole moment of 5 x 10-4 A • m2. The moment initially is aligned with a 0.5-T magnetic field. To rotate the loop so its dipole moment is perpendicular to the field and hold it in that orientation, you must do work of:
2.5 × 10-4 J
14
A charged capacitor and an inductor are connected in series. At time t = 0 the current is zero,but the capacitor is charged. If T is the period of the resulting oscillations, the next time after t = 0 that the current is a maximum is:
T/4
15
A charged capacitor and an inductor are connected in series. At time t = 0 the current is zero, but the capacitor is charged. If I is the period of the resulting oscillations, the next time after t = 0 that the voltage across the inductor is a maximum is:
T/2
16
A charged capacitor and an inductor are connected in series. At time t = 0 the current is zero, but the capacitor is charged. If I is the period of the resulting oscillations, the next time after t = 0 that the energy stored in the magnetic field of the inductor is a maximum is:
T/4
17
A capacitor in an LC oscillator has a maximum potential difference of 15 V and a maximum energy of 360 J. At a certain instant the energy in the capacitor is 40 J. At that instant what is the potential difference across the capacitor?
5V
18
Which of the following has the greatest effect in decreasing the oscillation frequency of an LC circuit? Using instead:
2L and 2C
19
We desire to make an LC circuit that oscillates at 100 Hz using an inductance of 2.5 H. We also need a capacitance of:
1ųf
20
An LC circuit consists of a 1-uF capacitor and a 4 mH inductor. Its oscillation frequency is approximately:
2500 Hz
21
An LC circuit has an oscillation frequency of 105 Hz. If C = 0.1 uF, then L must be about:
25ųH
22
Radio receivers are usually tuned by adjusting the capacitor of an LC circuit. If C = C1 for a frequency of 600 kHz, then for a frequency of 1200 kHz one must adjust C to:
C1/4
23
An LC series circuit with an inductance L and a capacitance C has an oscillation frequency f. Two inductors, each with inductance L, and two capacitors, each with capacitance C, are all wired in series and the circuit is completed. The oscillation frequency is:
f
24
The electrical analog of a spring constant k is:
1/C
25
A 150-g block on the end of a spring with a spring constant of 35 N/m is pulled aside 25 cm and released from rest. In the electrical analog the initial charge on the capacitor is:
0.025 C
26
A 150g block on the end of a spring with a spring constant of 35 N/m is pulled aside 25 cm and released from rest. In the electrical analog the maximum charge on the capacitor is 0.25 C. The maximum current in the LC circuit is:
0.38A
27
A capacitor in an LC oscillator has a maximum potential difference of 15 V and a maximum energy of 360 J. At a certain instant the energy in the capacitor is 40 J. At that instant what is the potential difference across the capacitor?
5V
28
A capacitor in an LC oscillator has a maximum potential difference of 15 V and a maximum energy of 360 pJ. At a certain instant the energy in the capacitor is 40 J. At that instant what is the emf induced in the inductor?
10v
29
In an oscillating LC circuit, the total stored energy is U. The maximum energy stored in the capacitor during one cycle is:
U
30
In an oscillating LC circuit, the total stored energy is U and the maximum charge on the capacitor is Q. When the charge on the capacitor is Q/2, the energy stored in the inductor is:
3U/4
31
The total energy in an LC circuit is 5.0 × 10-6 J. If C = 15 F the charge on the capacitor is:
12ųC
32
The total energy in an LC circuit is 5.0 × 10-6 J. If L = 25 mH the maximum current is:
20mA
33
At time t = 0 the charge on the 50-uF capacitor in an LC circuit is 15 C and there is no current. If the inductance is 20 mH the maximum current is:
15mA
34
An LC circuit has a capacitance of 30 uF and an inductance of 15 mH. At time t = 0 the charge on the capacitor is 10 C and the current is 20 mA. The maximum charge on the capacitor is:
17ųC
35
An LC circuit has an inductance of 15 mH and a capacitance of 10 F. At one instant the charge on the capacitor is 25 C. At that instant the current is changing at the rate of:
170A/s
36
An LC circuit has a capacitance of 30 F and an inductance of 15 mH. At time t = 0 the charge on the capacitor is 10 C and the current is 20 mA. The maximum current is:
25mA
37
An RLC circuit has a resistance of 200 $ and an inductance of 15 mH. Its oscillation frequency is 7000 Hz. At time t = 0 the current is 25 mA and there is no charge on the capacitor. After five complete cycles the current is:
2.1 × 10-4 A
38
An RLC circuit has an inductance of 25 mH and a capacitance of 5.0 F. The charge on the capacitor does NOT oscillate but rather decays exponentially to zero. The resistance in the circuit must be:
greater than or equal to 20, 0000 B.
39
A series circuit with an inductance of 15 mH, a capacitance of 35 MF, and a resistance of 5.05 contains a sinusoidal source of emf with a frequency of 500 Hz. The frequency with which the charge on the capacitor oscillates is:
500 Hz
40
The rapid exponential decay in just a few cycles of the charge on the plates of capacitor in an RLC circuit might be due to:
a large resistance
41
An RLC circuit has a capacitance of 12 F, an inductance of 25 mH, and a resistance of 605. The current oscillates with an angular frequency of:
1.4 × 103 rad/s
42
The angular frequency of a certain RLC series circuit is wo. A source of sinusoidal emf, with angular frequency 2w, is inserted into the circuit. After transients die out the angular frequency of the current oscillations is:
2wo
43
An RLC circuit has a sinusoidal source of emf. The average rate at which the source supplies energy is 5nW. This must also be:
the average rate at which energy is dissipated in the resistor