Section 24.2
Forces Caused by Magnetic Fields
Practice Test
1.
In Figure 24-16, if the current in the wire were reversed, what would the direction of the magnetic force be?
a.
down
b.
up
c.
right
d.
left
Hint
2.
How does an electric motor rotate 360 degrees?
a.
As the split ring reaches vertical, each half of the ring switches brushes and reverses the direction of current in the wire loop.
b.
A galvanometer changes the direction.
c.
A magnet moves through an electrical field.
d.
A wire spins the wheel.
Hint
3.
If a current is traveling toward you in a wire, what is the direction of the magnetic field?
a.
clockwise
b.
toward you
c.
away from you
d.
counterclockwise
Hint
4.
A 10-m long wire carrying 5 A of current is at right angles to a uniform magnetic field of 0.01 T. What is the magnitude of the force on the wire?
a.
0.5 N
b.
50 N
c.
5 N
d.
0.05 N
Hint
5.
The speed of an electric motor is controlled by varying the __________ through the motor.
a.
voltage
b.
direction of the north pole
c.
current
d.
resistance
Hint
6.
In Figure 24-16, if the magnetic poles were reversed, what would the direction of the magnetic force be?
a.
right
b.
up
c.
left
d.
down
Hint
7.
A magnetic field is generated __________ the direction of current in a wire.
a.
perpendicular to
b.
opposite of
c.
in the same direction as
d.
parallel to
Hint
8.
A beam of protons travels at 3.5 × 10E6 m/s through a uniform magnetic field of 5.7×10
-2
T. The beam of electrons is perpendicular to the field. How strong is the force acting on each proton?
a.
1.6×10
-12
N
b.
-6.4×10
-14
N
c.
3.2×10
-12
N
d.
3.2×10
-14
N
Hint
9.
Two straight wires that are parallel to each other are carrying currents in opposite directions. What happens to the wires?
a.
They stop carrying current because the current directions cancel each other out.
b.
They attract each other.
c.
Nothing happens.
d.
They repel each other.
Hint
10.
A straight wire that carries a 4.6-A current is in a uniform magnetic field oriented at right angles to the wire. The magnetic field has a strength of 1.2 T. If the force exerted on the wire is 0.60 N, what length of wire is in the magnetic field?
a.
0.11 m
b.
3.3 m
c.
2.3 m
d.
0.16 m
Hint
11.
If there were no current in the wire in Figure 24-16, what impact, if any, would that have on the magnetic force shown?
a.
The force would be reduced, but still point upwards.
b.
The force would remain the same.
c.
The force would be directed toward the south pole shown.
d.
There would be no force.
Hint
12.
A straight current-carrying wire is in a uniform magnetic field oriented at right angles to the wire. 0.14 m of wire is in the 0.72-T field. If the force on the wire is 0.33 N, what is the current in the wire?
a.
0.064 A
b.
3.3 A
c.
1.7 A
d.
0.13 A
Hint
13.
A(n) __________ uses electromagnetism to measure small currents.
a.
galvanometer
b.
ammeter
c.
ohmmeter
d.
voltmeter
Hint
14.
If a magnetic field points upward and the current is to your left, the force is __________.
a.
away from you
b.
to your right
c.
toward you
d.
to your left
Hint
15.
A magnetic field exerts a force on __________.
a.
only small particles
b.
all charged particles, regardless of size
c.
only electrons
d.
only wires
Hint
16.
An electron moving at 5.6×10
7
m/s travels through a uniform magnetic field of 1.4 T at right angles to the field. How strong is the force that acts on the electron?
a.
-1.3×10
-11
N
b.
2.2×10
-11
N
c.
1.5×10
-11
N
d.
-3.7×10
-11
N
Hint
17.
The force on an electron from a magnetic field is __________.
a.
so small it cannot be measured
b.
in the same direction as indicated by the third right hand rule
c.
opposite the direction indicated by the third right hand rule
d.
in the same direction as the magnetic field
Hint
18.
In Figure 24-16, if the magnetic poles were reversed AND the current in the wire were reversed, what would the direction of the magnetic force be?
a.
left
b.
right
c.
down
d.
up
Hint
