Physics 1B Quiz 4 Practice (Ch 19)
This question and the next two pertain to the the following situation.
(1) An electron (mass 9.11 × 10-31 kg, charge 1.6 × 10-19 C) moves rightward at speed 105
m/s as it passes from a field-free region into a region where there is a magnetic field of
strength B = 0.03 T. Shortly thereafter, it exits, moving leftward back into the region
where B = 0.
Find L, the distance between where the electron entered the field and where it exited the
field. (d)
(a) 22 µm
(b) 26 µm
(c) 32 µm
(d) 38 µm
(e) 44 µm
(2) In which direction does this magnetic field point? (b)
(a) into the page
(b) out of the page
(3) How much time did the electron spend in the region where the magnetic field B = 0.03 T
? (b)
(a) 0.38 ns
(b) 0.6 ns
(c) 1.2 ns
This question and the next two pertain to the the following situation.
(4) Consider two parallel wires, one carrying current I1 = 20 A to the right, and at a distance
L = 8 cm below it, another carrying I2 = 12 A to the left.
What is the magnetic field a distance 5 cm below the top wire (3 cm above the bottom
one)? (e)
(a)
(b)
(c)
(d)
(e)
1.6 × 10-4 T, out of page
8.0 × 10-5 T, out of page
0
8.0 × 10-5 T, into page
1.6 × 10-4 T, into page
(5) Do the two wires attract each other? (b)
(a) yes, they attract each other
(b) no, they do not attract each other
(6) The solenoid shown has a radius of 3 cm and 200 turns of wire along an 18 cm axis.
What constant current would be required to produce a magnetic field B = 0.01 T in the
interior of this solenoid? (a)
(a) 7.2 A
(b) 43 A
(c) 240 A
This and the next two questions pertain to the following situation.
Given are two long wires carrying currents. The first is located at (x = 0, y = 1 m) and
carries a current of 2 A directed out of the page. The second is located at (x = 0, y = -1 m)
and carries a current of 1 A directed into the page. (See the figure.)
(7) What is the magnitude of the magnetic field at the origin? (c)
(a)
(b)
(c)
(d)
(e)
1 × 10-7 T
3 × 10-7 T
6 × 10-7 T
12 × 10-7 T
20 × 10-7 T
(8) What is the direction of the magnetic field at the origin? (d)
(a)
(b)
(c)
(d)
(e)
zero
+y direction
-x direction
+x direction
-y direction
(9) What should one do to maximize the magnitude of the magnetic force acting on a
charged particle moving in a magnetic field? (a)
I. Maximize the strength of the magnetic field
II. Minimize the particle's velocity
III. Ensure that the particle is moving in the same direction as the magnetic field lines
(a)
(b)
(c)
(d)
(e)
I only
I and II only
I and III only
II and III only
I, II, and III
(10)
The solenoid shown below has length l = 0.15 m and cross-sectional area A = 3.5
-4 2
× 10 m . Its self-inductance is L = 25 mH. A current I of 2.5 amps flows through its
coils in the direction shown in the figure.
Which way does the magnetic field point inside the solenoid? (b)
(a) to the left
(b) to the right
(11)
A positively charged particle in a uniform external magnetic field moves in a
circular path in the clockwise direction, parallel to the plane of the page. In what
direction do the magnetic field lines point? (a)
(a)
(b)
(c)
(d)
(e)
out of the page
into the page
to the left
to the right
in a clockwise pattern parallel to the plane of the page
(12)
A particle is placed in a uniform magnetic field of strength 1 T. The particle has a
velocity of 400 m/s, perpendicular to the magnetic field. If the particle moves in a circle
of radius 4 m, what is its ratio of charge to mass (q/m), in Coulombs per kg?(d)
(a)
(b)
(c)
(d)
(e)
q/m = 0 C/kg
q/m = 25 C/kg
q/m = 50 C/kg
q/m = 100 C/kg
q/m = 200 C/kg
(13)
We represent the magnetic fields created by permanent magnets with magnetic
field lines. Choose the best answer about magnetic field lines. (a)
a. Magnetic field lines are closer together in regions where the magnetic field is
stronger.
b. Magnetic field lines start on the north end of the magnet and end on the south end
of the magnet (i.e. magnetic field lines have definite beginnings and endings).
c. Magnetic field lines point in the direction of the magnetic force on a moving,
positive charge.
d. Choices a, b, and c are all true.
e. Only choices b and c are true.
(14)
A charged particle moves in a straight line through a region of space where a
magnetic field is present. Which of the following answers must is true? (b)
a. The magnetic field has a magnitude of 0 T.
b. There is no component of the magnetic field perpendicular to the particle’s
velocity.
c. There is no component of the magnetic field parallel to the particle’s velocity.
d. The particle feels the maximum magnetic torque due to the magnetic field.
e. The particle is an electron.
(15)
A particle with charge +2.25 x 10-15C enters a magnetic field of 0.500 T in a
direction perpendicular to the field. Its velocity when it enters the magnetic field is
5.00 x 105 m/s. The particle exits the magnetic field 0.250 m from where it entered. Its
path is shown with a dotted line in the picture
below. What is the particle’s mass? (b)
a.
b.
c.
d.
e.
1.41 x 10-10 kg
2.81 x 10-22 kg
5.62 x 10-20 kg
9.00 x 10-27 kg
1.67 x 10-27 kg
(16)
Two wires are placed next to each other as shown below. Both wires carry
currents of 1.0 A down in the plane of the paper. Which answer below
describes the force on both wires?(c)
a. The force on wire 1 is to the left and the force on wire 2 is to
the left.
b. The force on wire 1 is to the left and the force on wire 2 is to
the right.
c. The force on wire 1 is to the right and the force on wire 2 is to
the left.
d. The force on wire 1 is to the right and the force on wire 2 is to
the right.
e. There is no force on either wire.
In the picture, a very long wire intersecting the page perpendicularly at the origin
carries a current of 4.0 A into the page. Another wire intersects the page
perpendicularly at (-2.0 m,0 m) and carries current of 4.0 A out of the page.
(17)
What is the magnitude of the magnetic field at point P due to the two currentcarrying wires? (d)
a.
b.
c.
d.
e.
0T
4.0 x 10-7 T
5.7 x 10-7 T
8.0 x 10-7 T
1.1 x 10-6 T
(18)
The figure below shows an edge view of two identical current-carrying loops
oriented as shown in a uniform magnetic field.
Compare the magnitude of the torque t1 on loop #1 with the torque t2 on loop #2 at the
instant shown. (c)
(a) t1 > t2
(b) t1 = t2
(c) t1 < t2
(19)
An electron feels a magnetic force due west after entering a uniform magnetic
field directed due north. (Neglect the earth’s own magnetic field.) The electron
experiences the maximum magnetic force possible in the magnetic field given its speed.
In which direction was its initial velocity? (d)
a.
b.
c.
d.
e.
North
South
West
Towards the center of the earth
Opposite of the center of the earth
(20)
A segment of flexible current-carrying wire is exposed to a region with a uniform
magnetic field, as shown below. What direction of magnetic field B
would create the bend shown below in the current-carrying wire?
(b)
a.
b.
c.
d.
e.
Into the page
Out of the page
In the plane of the page, directed left
In the plane of the page, directed right
In the plane of the page, directed down