Download 1. Five equal 2.0-kg point masses are arranged in the x

Phys 121 Exam 3 Makeup spring 2008
Name______________________________________________Sect___________
1. For the RC circuit shown ( R = 2M, C = 3 F and  = 300 V) how long will take for the current to
reach value of 77 A after the switch is closed?
A. 1 s
B. 2 s
C. 3 s
D. 4 s
E. 5 s
2. An electron moving with a speed of 2x10 5 m/s enters a region between two parallel plates separated by d = 20 mm with a potential
difference of V = 100 V between them. The electron is moving perpendicular to the electric field of the plates when it enters the region
between the plates. What uniform magnetic field , perpendicular to both the electron path and the electric field, must be applied for the
electron not be deflected?
A.
B.
C.
D.
E.
10 mT
15 mT
20 mT
25 mT
30 mT
3 – 4. Two long, straight wires are parallel and carry the same current of i 1 = i2 = 6 A in the opposite direction as shown.
3. If the distance between the wires is 6 cm, and the distance from wire 1 to point B is 2 cm what are the direction
and the magnitude of the net magnetic field at point B seen in figure.
A. 3.5x10-5 T into the page
B. 4.5x10-5 T into the page
C. 1.6x10-4 T out of the page
D. 2.0x10 -4T into the page
E. 8.0x10-3 T out of the page
4. What are the direction and the magnitude of the force per unit length F/L that the wire 1 exerts on the wire 2?
A. 1.2 x10-4 N, to the left
B. 1.2 x10-4 N, to the right
C. 5.0 x10-3 N, up
D. 5.0x10-3 N, down
E. 0.8x10-3 N, to the page
5. An electron with charge 1.6.10-19C and mass 9.11x10-31 kg is moving with a velocity v=2.105 m/s in the negative z
direction. A magnetic field B = 0.125 mT is pointing in the negative x direction . Find the frequency of electron
circular motion.
A)
B)
C)
D)
E)
1.9 MHz
2.2 MHz
3.5 MHz
4.2 MHz
5.1 MHz
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6. When electron moving in the plane of the page in the direction indicated by the arrow enters the
magnetic field directed down the page, the force on the electron is directed
A) out of the page
B) toward the left
C) into the page
D) toward the top of the page
E) toward the bottom of the page
7. What current is required in the windings of a 2000-turn solenoid 25 cm long in order to produce inside the solenoid a magnetic field
of magnitude 4x10-3 T?
A) 0.1 A
B) 0.2 A
C) 0.3A
D) 0.4 A
E) 0.5 A
8. Equivalent resistance of the circuit shown is closest to
A)
B)
C)
D)
E)
12 Ω
19 Ω
26 Ω
48 Ω
122 Ω
9. The current in the loop is 2 A counterclockwise , the radius of the larger semi-loop is 25 cm and radius of the smaller semi-loop is 8
cm. What is the magnitude of the magnetic fields at C?
A. 1.04 x10-5 T
B. 2.08 x10-5 T
C. 2.67 x10-4 T
D. 5.0x10-3 T
E. 0.8x10-3 T
10. An infinitely-long wire carrying a current of 100 A is bent into a loop with radius 10 cm as shown. What is the magnetic field
(magnitude and direction) at the center of the loop?
A) 0.4 mT, out of the page
B) 0.4 mT, into the page
C) 0.8 mT, out of the page
D) 0.8 mT, into the page
E) 1.6 mT, into the page
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11. In a mass spectrometer, an ion will have a greater radius for its circular path if:
A) its speed is smaller.
B) its mass is greater.
C) its charge is greater.
D) the magnetic field is stronger.
E) the magnetic field is 0.
12. A particle with positive charge q = 5x10-6 C is a distance 1.5 cm from a long straight wire that carries a
current 5 A. The particle is traveling with speed 12000 m/s perpendicular to the wire as shown in the figure.
What are the direction and magnitude of the force on the particle if it is moving away from the wire?
A) 1.0x10-7 N, up
B) 1.0x10-7 N, down
C) 2.0x10-8 N, up
D) 4.0x10-6 N, down
E) 4.0x10-6 N, up
Workout problem 1 ( 3 points) Show your work
In the circuit shown, one resistor has the twice the value of the second resistor R. Suppose switch S is
initially closed.
a) What is the charge stored in the capacitor?
b) When it is then opened what is the potential difference across the capacitor 3 sec later if R = 1.5M,
C = 2 F and  = 30 V?
Workout problem 2 (2 points)
2. Two long wires are oriented so that they are perpendicular to each other, and at their closest, they are 20 cm apart. What is the
magnitude of the magnetic field at a point midway between them if the top one carries a current of 20-A and the bottom one caries 10-A?
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