Chapter 34 electromagnetic induction
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Chapter 34. Electromagnetic Induction. Electromagnetic induction is the scientific principle that underlies many modern technologies, from the generation of electricity to communications and data storage. Chapter Goal: To understand and apply electromagnetic induction.

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Chapter 34. Electromagnetic Induction

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Chapter 34 electromagnetic induction

Chapter 34. Electromagnetic Induction

Electromagnetic induction is the scientific principle that underlies many modern technologies, from the generation of electricity to communications and data storage.

Chapter Goal: To understand and apply electromagnetic induction.


Chapter 34 electromagnetic induction1

Chapter 34. Electromagnetic Induction

Topics:

  • Induced Currents

  • Motional emf

  • Magnetic Flux

  • Lenz’s Law

  • Faraday’s Law

  • Induced Fields

  • Induced Currents: Three Applications

  • Inductors

  • LC Circuits

  • LR Circuits


Chapter 34 reading quizzes

Chapter 34. Reading Quizzes


Chapter 34 electromagnetic induction

Currents circulate in a piece of metal that is pulled through a magnetic field. What are these currents called?

  • Induced currents

  • Displacement currents

  • Faraday’s currents

  • Eddy currents

  • This topic is not covered in Chapter 34.


Chapter 34 electromagnetic induction

Currents circulate in a piece of metal that is pulled through a magnetic field. What are these currents called?

  • Induced currents

  • Displacement currents

  • Faraday’s currents

  • Eddy currents

  • This topic is not covered in Chapter 34.


Chapter 34 electromagnetic induction

Electromagnetic induction was discovered by

  • Faraday.

  • Henry.

  • Maxwell.

  • Both Faraday and Henry.

  • All three.


Chapter 34 electromagnetic induction

Electromagnetic induction was discovered by

  • Faraday.

  • Henry.

  • Maxwell.

  • Both Faraday and Henry.

  • All three.


Chapter 34 electromagnetic induction

The direction that an induced current flows in a circuit is given by

  • Faraday’s law.

  • Lenz’s law.

  • Henry’s law.

  • Hertz’s law.

  • Maxwell’s law.


Chapter 34 electromagnetic induction

The direction that an induced current flows in a circuit is given by

  • Faraday’s law.

  • Lenz’s law.

  • Henry’s law.

  • Hertz’s law.

  • Maxwell’s law.


Chapter 34 basic content and examples

Chapter 34. Basic Content and Examples


Faraday s discovery

Faraday’s Discovery

Faraday found that there is a current in a coil of wire if and only if the magnetic field passing through the coil is changing. This is an informal statement of Faraday’s law.


Chapter 34 electromagnetic induction

Magnetic data storage encodes information in a pattern of alternating magnetic fields. When these fields move past a small pick-up coil, the changing magnetic field creates an induced current in the coil. This current is amplified into a sequence of voltage pulses that represent the 0s and 1s of digital data.


Motional emf

Motional emf

The motional emf of a conductor of length l moving with velocity v perpendicular to a magnetic field B is


Example 34 1 measuring the earth s magnetic field

EXAMPLE 34.1 Measuring the earth’s magnetic field

QUESTION:


Example 34 1 measuring the earth s magnetic field1

EXAMPLE 34.1 Measuring the earth’s magnetic field


Example 34 1 measuring the earth s magnetic field2

EXAMPLE 34.1 Measuring the earth’s magnetic field


Example 34 1 measuring the earth s magnetic field3

EXAMPLE 34.1 Measuring the earth’s magnetic field


Magnetic flux can be defined in terms of an area vector

Magnetic flux can bedefined in terms of an area vector


Magnetic flux

Magnetic Flux

The magnetic flux measures the amount of magnetic field passing through a loop of area A if the loop is tilted at an angle θ from the field, B. As a dot-product, the equation becomes:


Example 34 4 a circular loop in a magnetic field

EXAMPLE 34.4 A circular loop in a magnetic field

QUESTION:


Example 34 4 a circular loop in a magnetic field1

EXAMPLE 34.4 A circular loop in a magnetic field


Lenz 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 magnetic field opposes the change in the flux.


Tactics using lenz s law

Tactics: Using Lenz’s Law


Faraday s law

Faraday’s Law

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

and the direction of the emf is such as to drive an induced current in the direction

given by Lenz’s law.


Problem solving strategy electromagnetic induction

Problem-Solving Strategy: Electromagnetic Induction


Inductance of a solenoid

Inductance of a solenoid

The inductance of a solenoid having N turns, length l and cross-section area A is


Example 34 12 the length of an inductor

EXAMPLE 34.12 The length of an inductor

QUESTION:


The potential difference across an inductor

The potential difference across an inductor

The potential difference across an inductor with an inductance of L and carrying a current I is


Example 34 13 large voltage across an inductor

EXAMPLE 34.13 Large voltage across an inductor

QUESTION:


Example 34 13 large voltage across an inductor1

EXAMPLE 34.13 Large voltage across an inductor


Example 34 13 large voltage across an inductor2

EXAMPLE 34.13 Large voltage across an inductor


Example 34 13 large voltage across an inductor3

EXAMPLE 34.13 Large voltage across an inductor


The current in an lc circuit

The current in an LC circuit

The current in an LC circuit where the initial charge on the capacitor is Q0 is

The oscillation frequency is given by


Example 34 15 an am radio oscillator

EXAMPLE 34.15 An AM radio oscillator

QUESTION:


Example 34 15 an am radio oscillator1

EXAMPLE 34.15 An AM radio oscillator


Chapter 34 summary slides

Chapter 34. Summary Slides


General principles

General Principles


General principles1

General Principles


General principles2

General Principles


Important concepts

Important Concepts


Important concepts1

Important Concepts


Applications

Applications


Applications1

Applications


Chapter 34 clicker questions

Chapter 34. Clicker Questions


Chapter 34 electromagnetic induction

A square conductor moves through a uniform magnetic field. Which of the figures shows the correct charge distribution on the conductor?


Chapter 34 electromagnetic induction

A square conductor moves through a uniform magnetic field. Which of the figures shows the correct charge distribution on the conductor?


Chapter 34 electromagnetic induction

Is there an induced current in this circuit? If so, what is its direction?

  • No

  • Yes, clockwise

  • Yes, counterclockwise


Chapter 34 electromagnetic induction

Is there an induced current in this circuit? If so, what is its direction?

  • No

  • Yes, clockwise

  • Yes, counterclockwise


Chapter 34 electromagnetic induction

A square loop of copper wire is pulled through a region of magnetic field. Rank in order, from strongest to weakest, the pulling forces Fa, Fb, Fc and Fd that must be applied to keep the loop moving at constant speed.

  • Fb = Fd > Fa = Fc

  • Fc > Fb = Fd > Fa

  • Fc > Fd > Fb > Fa

  • Fd > Fb > Fa = Fc

  • Fd > Fc > Fb > Fa


Chapter 34 electromagnetic induction

A square loop of copper wire is pulled through a region of magnetic field. Rank in order, from strongest to weakest, the pulling forces Fa, Fb, Fc and Fd that must be applied to keep the loop moving at constant speed.

  • Fb = Fd > Fa = Fc

  • Fc > Fb = Fd > Fa

  • Fc > Fd > Fb > Fa

  • Fd > Fb > Fa = Fc

  • Fd > Fc > Fb > Fa


Chapter 34 electromagnetic induction

A current-carrying wire is pulled away from a conducting loop in the direction shown. As the wire is moving, is there a cw current around the loop, a ccw current or no current?

  • There is no current around the loop.

  • There is a clockwise current around the loop.

  • There is a counterclockwise current around the loop.


Chapter 34 electromagnetic induction

A current-carrying wire is pulled away from a conducting loop in the direction shown. As the wire is moving, is there a cw current around the loop, a ccw current or no current?

  • There is no current around the loop.

  • There is a clockwise current around the loop.

  • There is a counterclockwise current around the loop.


Chapter 34 electromagnetic induction

A conducting loop is halfway into a magnetic field. Suppose the magnetic field begins to increase rapidly in strength. What happens to the loop?

  • The loop is pulled to the left, into the magnetic field.

  • The loop is pushed to the right, out of the magnetic field.

  • The loop is pushed upward, toward the top of the page.

  • The loop is pushed downward, toward the bottom of the page.

  • The tension is the wires increases but the loop does not move.


Chapter 34 electromagnetic induction

A conducting loop is halfway into a magnetic field. Suppose the magnetic field begins to increase rapidly in strength. What happens to the loop?

  • The loop is pulled to the left, into the magnetic field.

  • The loop is pushed to the right, out of the magnetic field.

  • The loop is pushed upward, toward the top of the page.

  • The loop is pushed downward, toward the bottom of the page.

  • The tension is the wires increases but the loop does not move.


Chapter 34 electromagnetic induction

The potential at a is higher than the potential at b. Which of the following statements about the inductor current I could be true?

  • I is from b to a and is steady.

  • I is from b to a and is increasing.

  • I is from a to b and is steady.

  • I is from a to b and is increasing.

  • I is from a to b and is decreasing.


Chapter 34 electromagnetic induction

The potential at a is higher than the potential at b. Which of the following statements about the inductor current I could be true?

  • I is from b to a and is steady.

  • I is from b to a and is increasing.

  • I is from a to b and is steady.

  • I is from a to b and is increasing.

  • I is from a to b and is decreasing.


Chapter 34 electromagnetic induction

Rank in order, from largest to smallest, the time constants τa, τb, and τc of these three circuits.

  • τa > τb > τc

  • τb > τa > τc

  • τb > τc > τa

  • τc > τa > τb

  • τc > τb > τa


Chapter 34 electromagnetic induction

Rank in order, from largest to smallest, the time constants τa, τb, and τc of these three circuits.

  • τa > τb > τc

  • τb > τa > τc

  • τb > τc > τa

  • τc > τa > τb

  • τc > τb > τa


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