Magnetic Field and Forces
1. A particle of charge +q enters a uniform magnetic field B directed into the page. The
direction of the magnetic force FB on the particle is
(A) top of the page
(B) bottom of the page
(C) Left
(D) Right
(E) out of the page
2. A particle of charge -q enters a uniform magnetic field B directed out of the page. The
direction of the magnetic force FB on the particle is
(A) top of the page
(B) bottom of the page
(C) Left
(D) Right
(E) out of the page
3. A particle of charge -q enters a uniform magnetic field B directed out of the page. The
direction of the magnetic force FB on the particle is
(A) top of the page
(B) bottom of the page
(C) Left
(D) Right
(E) no force applied
4. A charge particle –q enters a uniform magnetic field B. If FB is the magnetic force, which
of the following represents the particle’s velocity?
(A) qB/ FB
(B) q/ FBB
(C) FB/qB
(D) 1/ qFBB
(E) B/ qFB
.
5. A current carrying wire carries a current into the page. The wire is placed in a uniform
magnetic field directed to the right. The magnetic force on the current is directed
(A) top of the page
(B) bottom of the page
(C) left
(D) right
(E) into the page
6. A current carrying wire of length L and mass m is placed in a uniform magnetic field B.
The current in the wire is I. What must the direction of the field be in order to balance
the gravity?
(A) into the page
(B) bottom of the page
(C) right
(D) left
(E) out of the page
7. A current carrying wire of length L and mass m is placed in a uniform magnetic field. The
current in the wire is I. What must the magnitude of the field be in order to balance the
gravity?
(A)
𝑚𝑔
(B)
𝐼𝐿
𝑚𝐿
𝐼𝑔
𝐼𝑔
(C) 𝑔𝐿
𝐼𝑔
𝐼𝑙
(D) 𝑚𝐿
(E) 𝑚𝑔
8. A positive charges travels through a uniform magnetic field. The diagram represents the
direction of the particle’s velocity and magnetic force on it at the certain point. What is
the direction of the magnetic field B?
(A) out of the page
(B) into the page (C) right
(D) left
(E) top of the page
9. An electron experiences a magnetic force 4.8x10-13 N when entering a uniform magnetic
field of strength of2 T at a 30°angle to the magnetic field lines. Which of the following
represents the electron’s speed?
(A) 3x108
𝑚
𝑚
(B) 3x107 𝑠
𝑠
(C) 3x106
𝑚
𝑠
(D) 3x105
𝑚
𝑠
(E) 3x103
𝑚
𝑠
10. A negatively charged particle of charge q and mass m moves with constant speed v in a
circular path in the presence of a uniform field B. Which of following represents the
radius r of the moving charge?
(A)
𝑞𝐵
𝑚𝑣
(B)
𝑞𝑣
𝑚𝐵
(C)
𝑚𝐵
𝑞𝑣
(D)
𝑞𝐵𝑚
𝑣
𝑚𝑣
(E) 𝑞𝐵
11. An electron enters a region where both a magnetic field B into the page and electric
field E between the two plates act on the particle as shown above. What must be the
direction of the electric field in order for the particle to move in the straight line?
(A) top of the page
(B) bottom of the page
(C) Left
(D) Right
(E) Into the page
12. An electron enters a region where both a magnetic field B into the page and electric
field E between the two plates act on the particle as shown above. Which of the
following represents the particle’s velocity when it passes through the region of two
fields undeflected?
(A) E/B
(B) B/E
(C) B2/E
(C) B/√E
(E) E2/B
13. An electron enters a region where both a magnetic field B into the page and electric
field E between the two plates act on the particle as shown above. If the electric field is
removed which of the following represents the motion of the electron?
(A) To the right
(B) Parabolic path downward
(C) Parabolic path upward
(D) Circular path clockwise
(E) Circular path counter clockwise
14. An electric current flows in a closed loop made of two fixed rails, power supply, and very
light rod that is free to move on the top of the rails. A uniform magnetic field is
perpendicular to the plane of the circuit. What is the direction of magnetic force on the
rod?
(A) +y
(B) -Y
(C) -x
(D) +x
(E) +z
15. An electric current flows in a closed loop made of two fixed rails, power supply, and very
light rod of length L that is free to move on the top of the rails. A uniform magnetic field
B is perpendicular to the plane of the circuit. If current source supplies voltage V and net
resistance R, what is the magnitude of the magnetic force on the rod?
(A)
𝑉𝐵𝐿
𝑅
𝑉𝐵
(B) 𝑅𝐿
𝐵𝐿
(C) 𝑉𝑅
𝑉𝐿
(D) 𝐵𝑅
𝑉𝑅
(E) 𝐵𝐿
16. A rectangular piece of metal is placed in a uniform magnetic field and connected to a
battery on two opposite sides. Which one of the following statements is incorrect?
(A) The conventional current in the metal plate is directed from the left to the right
(B) The flow of electrons passes the metal plate from the right to the left
(C) Point L has higher potential than point N
(D) Point N has higher potential that point L
(E) The potential difference between point L and N is explained by Hall Effect
17. An electric current flows straight up. An electron approaches the current from East.
What is the direction of the magnetic force on the electron due to the current?
(A) East
(B) West
(C) North
(D) South
(E) Up
18. A positively charged particle moves in the region of an electric current placed below the
particle. What is the direction of magnetic force on the charge?
(A) Top the page (B) Bottom of the page (C) Left (D) Right (E) Out of the page
19. A uniform magnetic field B is parallel to the xy-plane and in the +y-direction, as shown
above. A positively charged particle initially moves with velocity v in the xy-plane at an
angle Ɵ to the magnetic field and the y-axis. Which of the following paths will the
particle follow in the presence of the magnetic field?
(A) Continue a straight-line path
(B) A circular path in the xy-plane
(C) A circular path in the yz-plane (D) A helical path with its axis parallel to the y-axis
(E) A helical path with its axis parallel to the z-axis
20. A uniform magnetic field B is parallel to the xy-plane and in the +y-direction, as shown
above. A positively charged particle q initially moves with velocity v in the xy-plane at
an angle Ɵ to the magnetic field and the y-axis. What is the magnitude of the force
acting on the charge?
(A) qvB
(B) qvB cosƟ
(C) qvB sinƟ
(D)qv/BsinƟ (E) qvB tanƟ
21. A proton moves parallel to the x-axis in the positive x-direction. What must the direction
of the electric field be in order to keep the proton going undeflected if the magnetic
field is established in +y direction?
(A) Positive y-direction
(B) Positive z-direction
(C) Negative x-direction
(D) Negative y-direction (E) Negative z-direction
22. A current-carrying loop of wire is placed in a uniform magnetic field perpendicular to
the plane of the loop. Under the influence of the magnetic force the loop will
(A) rotate with respect to its center (B) rotate with respect to its diameter
(C) contract (D) expand (E) stays stationary
23. A bar magnet and a wire loop carrying current I are arranged as shown above. What is
the direction of the force on the current loop due to the magnet?
(A) Toward the magnet
(B) Away from the magnet
(C) Toward the top of the page
(D) Toward the bottom of the page
(E) There is no force on the current loop.
24. A charged particle in a uniform magnetic field B moves in a circular path of radius r.
Which of the following represents the frequency of revolution f?
(A)
𝑞𝐵
2𝜋𝑚
𝑞𝑚
(B) 2𝜋𝐵
2𝜋𝐵
(C)
𝑞𝑚
(D)
𝑞𝐵𝑚
2𝜋
𝑞𝑚
(E) 2𝜋𝐵
I
v
25. A loop of wire has a current I running through it in a counter clockwise direction. An
electron moving with velocity v downward is placed outside of the loop and in the plane
of the loop. Which of the following represents the direction of the magnetic force due
to the loop on the electron?
(A)To the right
(B) To the left
(C) Into the page
(D) Out of the page
(E) To the top of the page
Answers
1. C
2. A
3. E
4. C
5. B
6. A
7. A
8. B
9. C
10. E
11. B
12. A
13. D
14. D
15. A
16. C
17. E
18. B
19. D
20. C
21. B
22. C
23. A
24. A
25. B