Physics 72: Chapter 27-28 Problem Set Part 2 Name: Lecturer: Mr Carlos Baldo III
Summer 2010 Score: Section: X7-7
Encircle the letter of the correct answer. Solve each problem clearly and completely for full credit. 1.
Solenoid. Current is flowing through the solenoid in the direction indicated by the arrows. What is the direction of the magnetic field inside the solenoid?
B
A
C
D
E. There is no magnetic field inside the solenoid.
2.
Parallel wires. Two parallel wires lie on the plane of this page and carry equal currents in the same direction. What is the direction of the net magnetic field at a point midway between the wires? A. A. Into the page B. B. Out of the page C. C. Parallel to the wires D. D. Anti-parallel to the wires E. E. There is no magnetic field at that field point
3.
Line and point. What should be the magnitude and direction of the current I on the infinitely long conducting wire such that the net magnetic field at P due to this wire and an electron traveling to the left at this instant is zero? A. Zero I B.
C.
D.
E.
ev 2 R , left ev 4 R , left ev 2 R , right ev 4 R , right
R P R v
−e
For the next two numbers, consider two electrons and three protons moving in different directions but with the same speed, as shown below. 4.
D-field. What is the direction of the magnetic field at point P? A. Upward B. Downward C. Into the page D. Out of the page E. No magnetic field at point P
5.
D-force. If a third electron is placed at point P with initial velocity directed into the page, what would be direction of the magnetic force acting on this electron? A. To the left B. To the right C. Upward D. Downward E. No magnetic force acting on the electron
Physics 72: Chapter 27-28 Problem Set Part 2
Summer 2010
6.
Magnetic Dipole. The plane of a 0.5m X 0.1m rectangular loop of wire is parallel to a 0.20T magnetic field. The loop carries a current of 2.0 A. What is the magnitude of the dipole moment of the loop? A. 0.2 N-m B. 2.0 N-m C. Zero D. 0.1 N-m E. 0.5 N-m
7.
Magnetic Dipole. What is the direction of magnetic moment µ when a loop of wire is immersed in a uniform external magnetic field (thick arrow)?
8.
Magnetic Force. A proton is released from rest in a region of uniform electric field E and magnetic field B as shown. Which line best describes the trajectory of the proton?
9.
Velocity Selector. An electron is moving downward through a chamber of uniform electric and magnetic field, with magnitudes of 5.0 N/C and 0.1 T, respectively as shown in the figure. If the charge is initially moving with a speed 50 m/s, which of the following statements is TRUE? (Assume zero air resistance, gravity, and friction.) A. The final velocity is less than 50 m/s to the right. B. The final velocity is greater than 50 m/s to the right. C. The final velocity is less than 50 m/s to the left. D. The final velocity is greater than 50 m/s to the right. E. The final velocity is the same as the initial velocity.
10. Ampere. Consider a wire with cross-sectional radius R (shown in the figure) and carries constant current I. What is the magnetic field at a point inside the wire where its distance from the center r < R? A. Zero
D.
µo I 2π r µo I 2π R µo IR 2π r 2
E.
µo Ir 2π R 2
B. C.
11. BDL. Which of the integration paths (A-E) has
∫ Bidl value?
Note: I is a the most negative non-zero current. The wires are placed in vacuum.
Physics 72: Chapter 27-28 Problem Set Part 2
Summer 2010
For the next two numbers, consider a coaxial cable consisting of a small cylinder (with radius R1) and a bigger hollow cylinder (with radius R2) carrying equal currents in opposite directions as shown. 12. Inside. What is the magnitude of the magnetic field at a point a distance r = R1 measured from the axes of the cylinders? A. Zero
B.
C.
D.
E.
µo I 2πR1 µo I 2πR2 µo I 4πR1 µo I 2π(R2 -R1 )
13. Outside. What is the magnitude of the magnetic field at a point a distance r measured from the center of the coaxial cable (where r > R2)? A. Zero
B.
C.
µo I 2πR1 µo I 2πR2
D.
E.
µo I 4πR1 µo I 2π(R2 -R1 )
For the next two numbers, consider the figure below. 14. Amp-peer 1. Which of the following statements is correct about line integral along paths A, B and C? A. The line integral along path A is positive. B. The line integral along path B is positive. C. The line integral along path C is positive. D. The line integral along paths A and B is the same. E. The line integral along paths A, B and C are the same. 15. Amp-peer 2. Determine the magnetic field at point P. A. Zero
7 µo I 12π a , upward 7µ I B= o 12π a , downward B=
B. C.
23µo I 12π a 23µo I B= 12π a B=
D. E.
, upward , downward
16. Soln. An electron moving with velocity given by What is the force acting on the electron?
v = 4ˆi − 2 ˆj − 3kˆ
A. zero
D.
B.
E.
C.
F = e( 9 ˆj − 6kˆ ) F = − e( 9 ˆj − 6kˆ )
is in a magnetic field given by
F = e( 9 ˆj + 6kˆ ) F = − e( 9 ˆj + 6kˆ )
B = 3iˆ .
Physics 72: Chapter 27-28 Problem Set Part 2
Summer 2010
17. PE. Consider the ff. orientations of a loop of wire that is free to rotate in a uniform magnetic field along the +z direction. At which orientation(s) is the potential energy maximum? A. A B. B C. C D. D E. All of the above
18. Naruto. A neutral conducting Naruto toy is hung and is raised at some angle Φ in a region of uniform magnetic field directed into the page. Which of the ff. statements is TRUE? A. As it moves to the left, negative charges accumulate on the head of the toy B. As it moves to the left, positive charges accumulate on the head of the toy C. The polarity of the head and the feet of the toy changes sign as it moves to the left and to the right D. A and C E. B and C 19. Star Wars. Spock drops a loop with front face labeled “tsa” in between two very long magnets as shown in the figure. The loop carries a counterclockwise current I. What will be the orientation of the loop at the instant it is exactly between the magnets? A. Tsa is facing out of the page B. Tsa is facing into the page C. Tsa is facing to the right D. Tsa is facing to the left E. Tsa is facing upward
+y
20. Non-uniform B. Consider a square loop of wire carrying a 1-A current in a region of non-uniform magnetic field. If the magnetic field varies with
10T ⋅ m ˆ B(x) = k x position as , what is the net magnetic force (magnitude
and direction) on the loop? A. zero B. C. D. E.
5 iˆ −5 iˆ 10 iˆ −10 iˆ
Non-uniform magnetic field
+x 0
1m
2m
+z
21. Moja-moja. Mojacko, who stole and swallowed a huge positive charge, was standing motionless so that no one can notice him. Unfortunately, he got caught in a criss-crossing uniform magnetic (downward) and electric (left) fields. Which of the following is the direction of the force acting on the charge inside Mojacko?
--- The SAND Prince ---