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Announcements

- Homework for tomorrow…
(Ch. 33, CQ4, Probs. 10, 12, & 29)

CQ1: CCW

CQ3: yes, up

33.2: B = 0.10 T, out of page

33.3: F = 1.0 N, B = 2.3 T

- Office hours…
MW 12:30-1:30 pm

TR 9-10 am

F 10-11 am

- Tutorial Learning Center (TLC) hours:
M 8-1 pm, 3-6 pm, W 8-1 pm, 2-6 pm

TR 8-6 pm, F 8-2 pm

Last time…

The magnetic flux of a uniformB-field passing through a loop is…

The magnetic flux of a non-uniform B-field passing through a loop is…

33.4Lenz’s Law

Consider the figure below showing a bar magnet being pushed toward the loop, increasing the flux through the loop..

- Which direction is the induced current in the loop?

33.4Lenz’s Law

Lenz’s Law

There IS an induced current in a closed, conducting loop if and only if the magnetic flux through the loop is changing.

The direction of the induced current is such that the induced B-field opposes the change in flux.

33.4Lenz’s Law

Consider the figure below showing a bar magnet being pushed toward the loop, increasing the flux through the loop..

- Which direction is the induced current in the loop?

There is an induced current in a closed, conducting loop if and only if the magnetic flux through the loop is changing.

The direction of the induced current is such that the induced B-field opposes the change in flux.

Quiz Question 1

The bar magnet is pushed toward the center of a wire loop. Which is true?

- There is a clockwise induced current in the loop.
- There is a counterclockwise induced current in the loop.
- There is no induced current in the loop.

Quiz Question 2

The bar magnet is pushed toward the center of a wire loop. Which is true?

- There is a clockwise induced current in the loop.
- There is a counterclockwise induced current in the loop.
- There is no induced current in the loop.

Using Lenz’s Law…

- Determine the direction of the applied B-field.
- The field must pass through the loop.

- Determine how the flux is changing.
- Determine the direction of the induced B-field that will oppose the change in the flux.
- Determine the direction of the induced current.

Quiz Question 3

The current in the straight wire is decreasing. Which is true?

- There is a clockwise induced current in the loop.
- There is a counterclockwise induced current in the loop.
- There is no induced current in the loop.

Quiz Question 4

The B-field is confined to the region inside the dashed lines; it is zero outside. The metal loop is being pulled out of the B-field. Which is true?

- There is a clockwise induced current in the loop.
- There is a counterclockwise induced current in the loop.
- There is no induced current in the loop.

Quiz Question 5

Immediately after the switch is closed, the lower loop exerts ____ on the upper loop.

- a torque
- an upward force
- a downward force
- no force nor torque

33.5Faraday’s Law

- An emf is induced in a conducting loop if the magnetic flux through the loop changes.
- The magnitude of the emf is:
The direction of the emf is such as to drive an induced current in the direction given by Lenz’s law.

Motional emf, revisited…

Motional emffor a conductor moving with velocity vperpendicular to the B-field…

The induced current in the circuit….

Using Faraday’s Law…

An emf is induced in a conducting loop if the magnetic flux through the loop changes.

so,

The direction of the emf is such as to drive an induced current in the direction given by Lenz’s law.

Using Faraday’s Law…

An emf is induced in a conducting loop if the magnetic flux through the loop changes.

so,

The direction of the emf is such as to drive an induced current in the direction given by Lenz’s law.

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