Clicker Question
Recall that
∫
 
E ⋅ dA = qenc /ε0
What is the total flux of the magnetic field through any
closed surface?
 
∫ B ⋅ dA = ?
A) zero
B) Ienc times a positive constant
C) -Ienc times a positive constant
Clicker Question
Recall that
∫
 
E ⋅ dA = qenc /ε0
What is the total flux of the magnetic field through any
closed surface?
 
∫ B ⋅ dA = ?
A) zero
B) Ienc times a positive constant
C) -Ienc times a positive constant
Clicker Question
A proton (+) and an electron (-) move side by side
both with velocity v as shown. What is the direction of
the magnetic field at the electron due to the proton (in
our “laboratory” frame of reference)?
A) into page
B) out of page
C) upward
D) downward
E) to the right
v
v
+
-
Clicker Question
A proton (+) and an electron (-) move side by side
both with velocity v as shown. What is the direction of
the magnetic field at the electron due to the proton (in
our “laboratory” frame of reference)?
A) into page
B) out of page
C) upward
D) downward
E) to the right
v
v
+
-
Clicker Question
A proton (+) and an electron (-) move side by side
both with velocity v as shown.The magnetic field is into
the page, by RHR.
What is the direction of the magnetic force on the e- ?
A) into page
B) out of page
C) upward
D) to the left
E) to the right
v
v
+
-
Clicker Question
A proton (+) and an electron (-) move side by side
both with velocity v as shown.The magnetic field is into
the page, by RHR.
What is the direction of the magnetic force on the e- ?
A) into page
B) out of page
C) upward
D) to the left
E) to the right
v
v
+
-
Clicker Question
A proton (+) and an electron (-) move side by side both
with velocity v as shown.
The total force on the electron is still attractive, but
weaker than if no magnetic force were present. What is
the total force on the electron if v=c?
A) 0
B) infinite, away from the proton
C) infinite, toward the proton
v
v
+
-
Clicker Question
A proton (+) and an electron (-) move side by side both
with velocity v as shown.
The total force on the electron is still attractive, but
weaker than if no magnetic force were present. What is
the total force on the electron if v=c?
A) 0
B) infinite, away from the proton
C) infinite, toward the proton
v
v
+
-
Clicker Question
Two positive point charges move side by side in
the same direction with the same velocity.
What is the direction of the magnetic force that
the upper point charge exerts on the lower one?
+q
+q
A. toward the upper point charge (the force is attractive)
B. away from the upper point charge (the force is
repulsive)
C. in the direction of the velocity
D. opposite to the direction of the velocity
E. none of the above
Clicker Question
Two positive point charges move side by side in
the same direction with the same velocity.
What is the direction of the magnetic force that
the upper point charge exerts on the lower one?
+q
+q
A. toward the upper point charge (the force is attractive)
B. away from the upper point charge (the force is
repulsive)
C. in the direction of the velocity
D. opposite to the direction of the velocity
E. none of the above
Clicker Question
y
A long straight wire lies along the y–axis and
carries current in the positive y–direction.
A positive point charge moves along the x–
axis in the positive x–direction. The
magnetic force that the wire exerts on the
point charge is in
A. the positive x–direction.
B. the negative x–direction.
C. the positive y–direction.
D. the negative y–direction.
E. none of the above
O
+q
I
x
Clicker Question
y
A long straight wire lies along the y–axis and
carries current in the positive y–direction.
A positive point charge moves along the x–
axis in the positive x–direction. The
magnetic force that the wire exerts on the
point charge is in
A. the positive x–direction.
B. the negative x–direction.
C. the positive y–direction.
D. the negative y–direction.
E. none of the above
O
+q
I
x
Clicker Question
The wire shown here is
infinitely long and has a 90°
bend. If current flows in the
wire as shown, what is the
direction of the magnetic
field at P due to the
current?
A. to the right
B. to the left
C. out of the plane of the figure
D. into the plane of the figure
E. none of these
Clicker Question
The wire shown here is
infinitely long and has a 90°
bend. If current flows in the
wire as shown, what is the
direction of the magnetic
field at P due to the
current?
A. to the right
B. to the left
C. out of the plane of the figure
D. into the plane of the figure
E. none of these
Clicker Question
A wire consists of two straight
sections with a semicircular
section between them. If current
flows in the wire as shown, what
is the direction of the magnetic
field at P due to the current?
A. to the right
B. to the left
C. out of the plane of the figure
D. into the plane of the figure
E. misleading question — the magnetic field at P is zero
Clicker Question
A wire consists of two straight
sections with a semicircular
section between them. If current
flows in the wire as shown, what
is the direction of the magnetic
field at P due to the current?
A. to the right
B. to the left
C. out of the plane of the figure
D. into the plane of the figure
E. misleading question — the magnetic field at P is zero
Clicker Question
Point P is at a perpendicular distance x from each wire
carry current I in the directions indicated. What is the
magnetic field B at point P?
I
A) 0
B) µoI/(2πx)
C) µoI/(πx)
D) not sure
E) all of the above
x
I
x
P
Clicker Question
Point P is at a perpendicular distance x from each wire
carry current I in the directions indicated. What is the
magnetic field B at point P?
I
A) 0
B) µoI/(2πx)
C) µoI/(πx)
D) not sure
E) all of the above
x
I
x
P
Clicker Question
The figure shows, in cross section,
three conductors that carry
currents perpendicular to the plane
of the figure.
If the currents I1, I2, and I3 all have the
same magnitude, for which path(s)
is the line integral of the magnetic
field equal to zero?
A. path a only
B. paths a and c
C. paths b and d
D. paths a, b, c, and d
E. The answer depends on whether the integral goes
clockwise or counterclockwise around the path.