A rectangular loop is placed in a uniform
magnetic field with the plane of the loop
perpendicular to the direction of the field.
If a current is made to flow through the loop
in the sense shown by the arrows, the field
exerts on the loop:
 

F  I  B

B
I
1. a net force.
2. a net torque.
3. a net force and a net torque.
4. neither a net force nor a net torque.
PI
A rectangular loop is placed in a uniform
magnetic field with the plane of the loop
parallel to the direction of the field.
If a current is made to flow through the loop
in the sense shown by the arrows, the field
exerts on the loop:
 

F  I  B

B
I
1. a net force.
2. a net torque.
3. a net force and a net torque.
4. neither a net force nor a net torque.
PI

What is A for this current loop?
 
  IA  B

2
y
z
1
a)
c)
b)  Izˆ
Izˆ
1 2
zˆ
d) 
1 2
zˆ
x

A rectangular loop of wire carries a current I in a magnetic field B
I
  IA  B
l1

B
S
N

l2
Top view
l2
z


B
Which of the following gives the torque on the
loop?
(a)   Il1B cos 
(b)  Il1l2 B cos 
(c)   Il1l2 B sin 
(d)   2 Il1l2 B sin 
(e)   Il1l2 B
y
x
i
o Loop area = A
θ

B
1. What is the magnetic flux through the wire loop of area A above?
(a) AB
(b) AB cosθ
(c) AB sinθ (d) zero
2. If θ is increased, which direction does the
induced current flow in the wire loop?
(a) i
(b) o
3. If θ is constant but B = B0 + αt, which direction does
the induced current flow? (a) i (b) o
i
o Loop area = A
θ

B
Φ = BA cosθ.
If θ is increased, what is the expression for the
induced voltage around the loop?
(a) V = B cosθ dA/dt (b) V = A cosθ dB/dt
(b) V = AB d cosθ /dt
A sphere of radius R is placed near a long,
straight wire that carries a steady current I.
The magnetic field generated by the current at
the sphere is B. The total magnetic flux
passing through the sphere is
(a) μ0 I
(b) μ0 I/(4πR2)
(c) 4πR2 μ0 I
(d) zero
(e) need more information
A uniform magnetic field is directed into the screen as
shown below. A loop of wire is moved to the right through
this field.
Does the magnetic flux through the loop,
into the screen,
(a) increase
(b) decrease
(c) remain the same
A uniform magnetic field is directed into the screen as
shown below. A loop of wire is moved to the right through
this field.
Is the direction of the induced current in
the loop
(a) clockwise
(b) counter-clockwise
(c) not enough information to tell
(d) there is no induced current
A non-uniform magnetic field is directed into the screen as
shown below. A loop of wire is moved to the right through
this field.
Does the magnetic flux through the loop,
into the screen,
(a) increase
(b) decrease
(c) remain the same
A non-uniform magnetic field is directed into the screen as
shown below. A loop of wire is moved to the right through
this field.
Is the direction of the induced current in
the loop
(a) clockwise
(b) counter-clockwise
(c) not enough information to tell
(d) there is no induced current
Consider a square loop made of 4 equal length conducting rods in a
uniform magnetic field in to the screen
a
b
1. If the corners ‘a’ and ‘b’ are pulled apart, does
the magnetic flux through the loop
(a) decrease
(b) increase
(c) stay the same
2. Is the induced current in the loop
(a) clockwise
(b) counter-clockwise
(c) there is no induced current
Is there an induced current in this circuit? If so, what is its
direction?
1. Yes, clockwise
2. Yes, counterclockwise
3. No
From Knight
A current-carrying wire is pulled away from a
conducting loop in the direction shown. As the
wire is moving, there is
(a) a clockwise current around the loop
(b) a counterclockwise current around the loop
(c) no current around the loop
From Knight
A conducting loop is
halfway into a magnetic
field. Suppose the magnetic
field begins to increase
rapidly in strength. What
happens to the loop?
(a) The loop is pushed toward the top of the
screen.
(b) The loop is pushed toward the bottom of the
page.
(c) The loop is pushed to the left.
(d) The loop is pushed to the right.
(e) The tension is the wires increases but the loop
does not move.
From Knight
In the figure below, when the bar magnet is inserted into the
coil, is the direction shown for induced current I
(a) correct?
(b) reversed?
(c) No current is induced in the coil.
B
I
I
Bar
magnet
into coil
N
B
I
I
A
B
front
2cm
wireloop
N

B
S
As the wire loop begins to enter the field of
the magnet, is the current in the loop
a) Zero
b) directed as shown
c) directed opposite to what is shown?
front
For the situation on the right,
which plot best represents the
magnetic flux through the
loop?
t
(b)
t


(c)

B
N


(a)
2cm
wireloop
t
(d)
t
v
S
3 cm
front
For the situation on the right,
which plot best represents the
current through the loop?
t
v
(b)
t
I
I
(c)
N
I
I
(a)
2cm
wireloop
t
(d)
t
S
3 cm