Download A proton is travelling at 2

Electromagnetism Review
(☺ indicates correct answer)
1. A proton is travelling at 2.3 x 106 m/s in a circular path in a 0.75 T magnetic
field. What is the magnitude of the force of the proton?
A. 1.6 x 10-24 N
B. 2.8 x 10-13 N ☺
C. 1.7 N
D. 2.9 x 10-21 N
2. A long conductor is placed in a 0.65 T magnetic field as shown below. What
are the magnitude and direction of the current that produces a 1.6 N force on the
wire directed up the page.
A.
B.
C.
D.
11 A Current; Direction: right ☺
11 A Current; Direction: left
4.4 A Current; Direction: right
4.4 A Current; Direction: left
3. Which of the following diagrams best represents the magnetic field in the
region between the two permanent magnets?
A.
B.
C.
D.
☺
4. A proton has a speed of 5.0 x 106 m/s while traveling perpendicular to a 0.14
T magnetic field. What is the magnetic force on the proton?
A. 8.4 x 10-21 N
B. 2.2 x 10-20 N
C. 1.6 x 10-26 N
D. 1.1 x 10-13 N ☺
5. A charged particle travels in a circular path in a magnetic field. What changes
to the magnetic field and to the velocity of the particle would both cause the
radius of its path to decrease?
A. Magnetic field change: increase; velocity change: increase
B. Magnetic field change: decrease; velocity change: increase
C. Magnetic field change: increase; velocity change: decrease ☺
D. Magnetic field change: decrease; velocity change: decrease
6. A beam of positively and negatively charged particles enters a magnetic field
as shown. Which paths illustrate the positive and negative charges leaving the
magnetic field region?
A. Positive: II; Negative: II
B. Positive: I; Negative: I
C. Positive: I; Negative: II ☺
D. Positive: II; Negative: I
7. The direction of a magnetic field is determined to be the direction in which
A. a positive charge would tend to move.
B. the north end of a compass needle would point. ☺
C. a negative charge would tend to move.
D. the south end of a compass needle would point.
8. Which diagram shows the magnetic field created near a conductor carrying
current towards the right?
A.
B.
☺
C.
D.
9.The diagram shows a conductor between a pair of magnets. The current in the
conductor flows out of the page. In what direction will the magnetic force act on
the conductor?
A.
B.
C.
D.
towards the left ☺
down the page
towards the right
up the page
10. In which diagram would the current-carrying conductor experience a
magnetic force out of the page?
A.
B.
C.
D.
☺
13. An ideal transformer has potential difference of 130 V ac across the primary
windings and a potential difference of 780 V ac across the secondary windings.
There are 390 turns in the secondary. The secondary current is
A. six times the primary current.
B. twice the primary current.
C. one-sixth the primary current. ☺
D. one half the primary current.
14. A transformer connected to a 120 V ac supply has 7 000 primary and 350
secondary windings. It delivers a secondary current of 2.4 A. Find the primary
current and secondary voltage.
A. Current: 48 A; Voltage: 6.0 V
B. Current: 0.12 A; Voltage: 2 400 V
C. Current: 48 A; Voltage: 2400 V
D. Current: 0.12 A; Voltage: 6.0 V ☺
15. The diagram below shows two coils in a magnetic field. An electric current
can be induced in the coil oriented with its plane
A. perpendicular to a changing magnetic field. ☺
B. parallel to a changing magnetic field.
C. parallel to a constant magnetic field.
D. perpendicular to a constant magnetic field.
16. Which of the following diagrams best shows the magnetic field due to a long
straight wire carrying conventional current I as shown?
A.
B.
C.
D.
☺
17. Define Lenz’s Law.
An electric current that is induced by a changing magnetic field will in turn
induce its own magnetic field. According to Lenz's law, the induced electric
current must be in such a direction that the magnetic field induced by the
current opposes the original cause of the induced current. The change is
the original magnetic field, or magnetic flux, induces the electric current.
For example, the original field is decreasing, then the induced magnetic
field must be in the same direction as the original field to oppose the
decrease.
Lenz's law is a consequence of the law of conservation of energy.
According to the law of conservation of energy the total amount of energy
in the universe must remain constant. Energy can be neither created nor
destroyed. Hence it is impossible to get free energy from nothing. Think
about this experiment similar to Faraday's original experiment. Push a bar
magnet through a coil of wire. The moving magnet induces an electric
current in the wire, which in turn induces its own magnetic field. According
to Lenz's law, the induced magnetic field opposes the cause, which is the
moving magnet. Hence the induced magnetic field is in a direction to try to
stop the moving magnet. If this were not the case, the induced magnetic
field would increase the magnet's velocity and thereby increase its kinetic
energy. There is no source for this energy. So if the induced magnetic field
helped rather than opposed its cause, conservation of energy would be
violated.
18. The diagram below shows a(n)…
A.
B.
C.
D.
E.
AC generator ☺
AC motor
DC generator
DC motor
19. Which diagram displays an AC motor?
A.
B.
20.
A
B ☺
In which diagram is pictured a ‘split ring commutator’?
A.
B.
A ☺
B