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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
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



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.


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.


Electromagnetic induction was through a magnetic field. What are these currents called?discovered by

  • Faraday.

  • Henry.

  • Maxwell.

  • Both Faraday and Henry.

  • All three.


Electromagnetic induction was through a magnetic field. What are these currents called?discovered by

  • Faraday.

  • Henry.

  • Maxwell.

  • Both Faraday and Henry.

  • All three.


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.


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.



Faraday s discovery
Faraday’s Discovery given by

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.


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 alternating magnetic fields. When these fields move past a small

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 alternating magnetic fields. When these fields move past a small

QUESTION:


Example 34 1 measuring the earth s magnetic field1
EXAMPLE 34.1 Measuring the earth’s magnetic field alternating magnetic fields. When these fields move past a small


Example 34 1 measuring the earth s magnetic field2
EXAMPLE 34.1 Measuring the earth’s magnetic field alternating magnetic fields. When these fields move past a small


Example 34 1 measuring the earth s magnetic field3
EXAMPLE 34.1 Measuring the earth’s magnetic field alternating magnetic fields. When these fields move past a small


Magnetic flux can be defined in terms of an area vector
Magnetic flux can be alternating magnetic fields. When these fields move past a small defined in terms of an area vector


Magnetic flux
Magnetic Flux alternating magnetic fields. When these fields move past a small

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 alternating magnetic fields. When these fields move past a small

QUESTION:


Example 34 4 a circular loop in a magnetic field1
EXAMPLE 34.4 A circular loop in a magnetic field alternating magnetic fields. When these fields move past a small


Lenz s law
Lenz’s Law alternating magnetic fields. When these fields move past a small

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 alternating magnetic fields. When these fields move past a small


Faraday s law
Faraday’s Law alternating magnetic fields. When these fields move past a small

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 alternating magnetic fields. When these fields move past a small


Inductance of a solenoid
Inductance of a solenoid alternating magnetic fields. When these fields move past a small

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 alternating magnetic fields. When these fields move past a small

QUESTION:


The potential difference across an inductor
The potential difference across an inductor alternating magnetic fields. When these fields move past a small

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 alternating magnetic fields. When these fields move past a small

QUESTION:


Example 34 13 large voltage across an inductor1
EXAMPLE 34.13 Large voltage across an inductor alternating magnetic fields. When these fields move past a small


Example 34 13 large voltage across an inductor2
EXAMPLE 34.13 Large voltage across an inductor alternating magnetic fields. When these fields move past a small


Example 34 13 large voltage across an inductor3
EXAMPLE 34.13 Large voltage across an inductor alternating magnetic fields. When these fields move past a small


The current in an lc circuit
The current in an LC circuit alternating magnetic fields. When these fields move past a small

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 alternating magnetic fields. When these fields move past a small

QUESTION:


Example 34 15 an am radio oscillator1
EXAMPLE 34.15 An AM radio oscillator alternating magnetic fields. When these fields move past a small


Chapter 34 summary slides
Chapter 34. Summary Slides alternating magnetic fields. When these fields move past a small


General principles
General Principles alternating magnetic fields. When these fields move past a small


General principles1
General Principles alternating magnetic fields. When these fields move past a small


General principles2
General Principles alternating magnetic fields. When these fields move past a small


Important concepts
Important Concepts alternating magnetic fields. When these fields move past a small


Important concepts1
Important Concepts alternating magnetic fields. When these fields move past a small


Applications
Applications alternating magnetic fields. When these fields move past a small


Applications1
Applications alternating magnetic fields. When these fields move past a small


Chapter 34 clicker questions
Chapter 34. Clicker Questions alternating magnetic fields. When these fields move past a small


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


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


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

  • No

  • Yes, clockwise

  • Yes, counterclockwise


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

  • No

  • Yes, clockwise

  • Yes, counterclockwise


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


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


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.


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.


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.


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.


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.


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.


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

  • τa > τb > τc

  • τb > τa > τc

  • τb > τc > τa

  • τc > τa > τb

  • τc > τb > τa


Rank in order, from largest to smallest, the time constants of the following statements about the inductor current 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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