INDUCTION
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Mag. Field applies force to moving charge
Moving Charge makes magnetic field.Current loops are mag. dipoles
Moving or Changing Mag. Field makes electric field (or EMF).
Elect. Charges Apply forces on one another
Elect. Charge Create fields
Electric Field is conservative - Potential
Electrostatics
Moving or Changing Mag. Field makes electric field (or EMF).
Faraday’s Law
Moving or Changing Mag. Field makes electric field (or EMF).
Faraday’s Law
ConcepTest 23.2a Moving Bar Magnet I
If a North pole moves toward the
loop from above the page, in
what direction is the induced
current?
1) clockwise
2) counterclockwise
3) no induced current
ConcepTest 23.2a Moving Bar Magnet I
If a North pole moves toward the
loop from above the page, in
what direction is the induced
current?
1) clockwise
2) counterclockwise
3) no induced current
The magnetic field of the moving bar magnet is pointing into the page and getting larger as the magnet moves closer to the loop. Thus the induced magnetic field has to point out of the page. A counterclockwise induced current will give just such an induced magnetic field.Follow-up: What happens if the magnet is stationary but the
loop moves?
S N
v
y
x
z
A magnet is moving toward a wire loop with velocity v as shown. In what direction is the magnetic field produced by the induced current in the loop?
a) + xb) + yc) - zd) - xe) + z
S N
v
y
x
z
The magnet has just passed through the loop and continues to move to the right. In what direction is the magnetic field produced by the induced current in the loop?
a) + xb) + yc) - zd) - xe) No field
ConcepTest 23.2b Moving Bar Magnet II
If a North pole moves toward
the loop in the plane of the
page, in what direction is the
induced current?
1) clockwise
2) counterclockwise
3) no induced current
Since the magnet is moving
parallel to the loop, there is
no magnetic flux through the
loop. Thus the induced
current is zero.
ConcepTest 23.2b Moving Bar Magnet II
If a North pole moves toward
the loop in the plane of the
page, in what direction is the
induced current?
1) clockwise
2) counterclockwise
3) no induced current
ConcepTest 23.1a Magnetic Flux I
In order to change
the magnetic flux
through the loop,
what would you
have to do?
1) drop the magnet
2) move the magnet upward
3) move the magnet sideways
4) only (1) and (2)
5) all of the above
Moving the magnet in any direction
would change the magnetic field
through the loop and thus the
magnetic flux.
ConcepTest 23.1a Magnetic Flux I
In order to change
the magnetic flux
through the loop,
what would you
have to do?
1) drop the magnet
2) move the magnet upward
3) move the magnet sideways
4) only (1) and (2)
5) all of the above
1) tilt the loop
2) change the loop area
3) use thicker wires
4) only (1) and (2)
5) all of the above
ConcepTest 23.1b Magnetic Flux II
In order to change
the magnetic flux
through the loop,
what would you
have to do?
1) tilt the loop
2) change the loop area
3) use thicker wires
4) only (1) and (2)
5) all of the above
Since F = B A cosq ,
changing the area or tilting
the loop (which varies the
projected area) would change
the magnetic flux through the
loop.
ConcepTest 23.1b Magnetic Flux II
In order to change
the magnetic flux
through the loop,
what would you
have to do?
30.4.1. Consider the situation shown. A triangular, aluminum loop is slowly moving to the right. Eventually, it will enter and pass through the uniform magnetic field region represented by the tails of arrows directed away from you. Initially, there is no current in the loop. When the loop is entering the magnetic field, what will be the direction of any induced current present in the loop?
a) clockwise
b) counterclockwise
c) No current is induced.
30.4.1. Consider the situation shown. A triangular, aluminum loop is slowly moving to the right. Eventually, it will enter and pass through the uniform magnetic field region represented by the tails of arrows directed away from you. Initially, there is no current in the loop. When the loop is entering the magnetic field, what will be the direction of any induced current present in the loop?
a) clockwise
b) counterclockwise
c) No current is induced.
30.4.2. Consider the situation shown. A triangular, aluminum loop is slowly moving to the right. Eventually, it will enter and pass through the uniform magnetic field region represented by the tails of arrows directed away from you. Initially, there is no current in the loop. When the loop is exiting the magnetic field, what will be the direction of any induced current present in the loop?
a) clockwise
b) counterclockwise
c) No current is induced.
30.4.2. Consider the situation shown. A triangular, aluminum loop is slowly moving to the right. Eventually, it will enter and pass through the uniform magnetic field region represented by the tails of arrows directed away from you. Initially, there is no current in the loop. When the loop is exiting the magnetic field, what will be the direction of any induced current present in the loop?
a) clockwise
b) counterclockwise
c) No current is induced.
30.4.3. A rigid, circular metal loop begins at rest in a uniform magnetic field directed away from you as shown. The loop is then pulled through the field toward the right, but does not exit the field. What is the direction of any induced current within the loop?
a) clockwise
b) counterclockwise
c) No current is induced.
30.4.3. A rigid, circular metal loop begins at rest in a uniform magnetic field directed away from you as shown. The loop is then pulled through the field toward the right, but does not exit the field. What is the direction of any induced current within the loop?
a) clockwise
b) counterclockwise
c) No current is induced.
30.4.5. A rectangular loop of wire is attached to a metal rod using rigid, electrically insulating rods so that the distance between the loop and metal rod is constant as the metal rod is rotated uniformly as shown. The metal rod carries a current in the direction indicated. Which of the following statements concerning an induced current in the rectangular loop as a result of the current in the metal rod is true?
a) The induced current in the loop is clockwise around the loop.
b) The induced current in the loop is counterclockwise around the loop.
c) The induced current in the loop alternates between clockwise and counterclockwise around the loop.
d) There is no induced current in the loop.
30.4.5. A rectangular loop of wire is attached to a metal rod using rigid, electrically insulating rods so that the distance between the loop and metal rod is constant as the metal rod is rotated uniformly as shown. The metal rod carries a current in the direction indicated. Which of the following statements concerning an induced current in the rectangular loop as a result of the current in the metal rod is true?
a) The induced current in the loop is clockwise around the loop.
b) The induced current in the loop is counterclockwise around the loop.
c) The induced current in the loop alternates between clockwise and counterclockwise around the loop.
d) There is no induced current in the loop.
1) clockwise
2) counterclockwise
3) no induced current
ConcepTest 23.4 Shrinking Wire Loop
If a coil is shrinking in a
magnetic field pointing
into the page, in what
direction is the induced
current?
The magnetic flux through the loop is decreasing, so the induced B field must try to reinforce it and therefore points in the same direction — into the page. According to the right-hand rule, an induced clockwise current will generate a magnetic field into the page.
1) clockwise
2) counterclockwise
3) no induced current
ConcepTest 23.4 Shrinking Wire Loop
If a coil is shrinking in a
magnetic field pointing
into the page, in what
direction is the induced
current?
Follow-up: What if the B field is oriented at 90° to its present direction?
ConcepTest 23.8a Loop and Wire I
A wire loop is being pulled away
from a current-carrying wire.
What is the direction of the
induced current in the loop?
I
1) clockwise
2) counterclockwise
3) no induced current
The magnetic flux is into the page on the right side of the wire and decreasing due to the fact that the loop is being pulled away. By Lenz’s Law, the induced B field will oppose this decrease. Thus, the new B field points into the page, which requires an induced clockwise current to produce such a B field.
I
ConcepTest 23.8a Loop and Wire I
A wire loop is being pulled away
from a current-carrying wire.
What is the direction of the
induced current in the loop?
1) clockwise
2) counterclockwise
3) no induced current
ConcepTest 23.8b Loop and Wire II
What is the induced current
if the wire loop moves in
the direction of the yellow
arrow ?
1) clockwise
2) counterclockwise
3) no induced current
I
The magnetic flux through the
loop is not changing as it
moves parallel to the wire.
Therefore, there is no induced
current.
I
1) clockwise
2) counterclockwise
3) no induced current
ConcepTest 23.8b Loop and Wire II
What is the induced current
if the wire loop moves in
the direction of the yellow
arrow ?
ConcepTest 23.9 Motional EMF
A conducting rod slides on
a conducting track in a
constant B field directed
into the page. What is the
direction of the induced
current?
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v
1) clockwise
2) counterclockwise
3) no induced current
ConcepTest 23.9 Motional EMF
A conducting rod slides on
a conducting track in a
constant B field directed
into the page. What is the
direction of the induced
current?
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v
The B field points into the page. The flux is increasing since the area is increasing. The induced B field opposes this change and therefore points out of the page. Thus, the induced current runs counterclockwise, according to the right-hand rule.
1) clockwise
2) counterclockwise
3) no induced current
Follow-up: What direction is the magnetic force on the rod as it moves?
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ConcepTest 23.3a Moving Wire Loop I
A wire loop is being
pulled through a uniform
magnetic field. What is
the direction of the
induced current?
1) clockwise
2) counterclockwise
3) no induced current
Since the magnetic field is
uniform, the magnetic flux
through the loop is not
changing. Thus no current is
induced.
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ConcepTest 23.3a Moving Wire Loop I
A wire loop is being
pulled through a uniform
magnetic field. What is
the direction of the
induced current?
1) clockwise
2) counterclockwise
3) no induced current
Follow-up: What happens if the loop moves out of the page?
1) clockwise
2) counterclockwise
3) no induced current
ConcepTest 23.3b Moving Wire Loop II
A wire loop is being
pulled through a uniform
magnetic field that
suddenly ends. What is
the direction of the
induced current?
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1) clockwise
2) counterclockwise
3) no induced current
ConcepTest 23.3b Moving Wire Loop II
A wire loop is being
pulled through a uniform
magnetic field that
suddenly ends. What is
the direction of the
induced current?
The B field into the page is
disappearing in the loop, so it must
be compensated by an induced flux
also into the page. This can be
accomplished by an induced current
in the clockwise direction in the
wire loop.
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Follow-up: What happens when the loop is completely out of the field?
1) clockwise
2) counterclockwise
3) no induced current
What is the direction of
the induced current if
the B field suddenly
increases while the loop
is in the region?
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ConcepTest 23.3c Moving Wire Loop III
1) clockwise
2) counterclockwise
3) no induced current
What is the direction of
the induced current if
the B field suddenly
increases while the loop
is in the region?
The increasing B field into the
page must be countered by
an induced flux out of the
page. This can be
accomplished by induced
current in the
counterclockwise direction in
the wire loop.
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ConcepTest 23.3c Moving Wire Loop III
Follow-up: What if the loop stops moving while the field increases?
lN turns
Solenoid - Inductor
Turn density -> n= N/l
N turns
Quick clicker. Immediately after switch is closed, what is the current in the circuit?
a) E/Rb) zeroc) E/2Rd) Not
enough info
Long after switch is closed, what is the current in the circuit?
a) E/Rb) zeroc) E/2Rd) Not
enough info
Immediately after switch closes,What is i1 ; i2?
i1 = i2= E/(R1+R2)
Long after switch closes,What is i1 ; i2?
i1 = E/R1 ; i2= 0
Immediately after switch is reopened, What is i1 ; i2?
i1 = 0 ; i2= E/R1
Long after switch is reopened, What is i1 ; i2?
i1 = 0 ; i2= 0
What is the value of the current through the inductor immediately after the switch is closed?
(a)V / 2R(b)V / R(c)Zero(d)V / 3R(e)V/L
R
L
V
What is the value of the current through the inductor long after the switch is closed?
(a)V / 2R(b)V / R(c)Zero(d)V / 3R(e)V/L
R
L
V