dfdafd Mag. Field applies force to moving charge Moving Charge makes magnetic field. Current loops...

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

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


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


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


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.

30.4.2. 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


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


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


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


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


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


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


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


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?

x x x x x x x x x x x




v

1) clockwise

2) counterclockwise


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?





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


Follow-up: What direction is the magnetic force on the rod as it moves?

x x x x x x x x x x x x







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


Since the magnetic field is

uniform, the magnetic flux

through the loop is not

changing. Thus no current is

induced.








ConcepTest 23.3a Moving Wire Loop I



magnetic field. What is


induced current?

1) clockwise

2) counterclockwise


Follow-up: What happens if the loop moves out of the page?

1) clockwise

2) counterclockwise


ConcepTest 23.3b Moving Wire Loop II



magnetic field that

suddenly ends. What is


induced current?

x x x x x

x x x x x

x x x x x

x x x x x

x x x x x

x x x x x

x x x x x

1) clockwise

2) counterclockwise


ConcepTest 23.3b Moving Wire Loop II



magnetic field that

suddenly ends. What is


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.

x x x x x

x x x x x

x x x x x

x x x x x

x x x x x

x x x x x

x x x x x

Follow-up: What happens when the loop is completely out of the field?

1) clockwise

2) counterclockwise


What is the direction of

the induced current if

the B field suddenly

increases while the loop

is in the region?








x x x x x

x x x x x

x x x x x

x x x x x

x x x x x

x x x x x

x x x x x

ConcepTest 23.3c Moving Wire Loop III

1) clockwise

2) counterclockwise


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.








x x x x x

x x x x x

x x x x x

x x x x x

x x x x x

x x x x x

x x x x x

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

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