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Chapter 20 Magnetic Flux Faraday’s Law PowerPoint PPT Presentation


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Lecture 31. Chapter 20 Magnetic Flux Faraday’s Law. 12 April 1999 Monday. Physics 112. Chapter 20. Induced Voltages and Inductance.

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Chapter 20 Magnetic Flux Faraday’s Law

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Chapter 20 magnetic flux faraday s law

Lecture 31

Chapter 20

Magnetic Flux

Faraday’s Law

12 April 1999

Monday

Physics 112


Chapter 20 magnetic flux faraday s law

Chapter 20

Induced Voltages and Inductance

We saw in Chapter 19 that moving charges (currents) create magnetic fields.Nature often reveals a great deal of symmetry. So, scientists wondered, “Can magnetic fields can create currents?” You might guess that the answer is, “Yes.” In this chapter, we’ll explore this physical process known as induction.


Chapter 20 magnetic flux faraday s law

A

_

+

Shortly after Oersted’s discovery that currents

create magnetic fields, Michael Faraday (England)

and Joseph Henry (US) conducted experiments

to determine if magnetic fields created electrical

currents...

Soft magnetic

material

primary coil

secondary coil

Secondary Circuit

Primary Circuit


Chapter 20 magnetic flux faraday s law

A

_

+

Faraday’s Observations:

With theswitch open, no readingon the ammeter.

When theswitch is closed, theammeter needle deflects momentarilytoward the right,then returns to 0.


Chapter 20 magnetic flux faraday s law

A

_

+

Faraday’s Observations:

With a constant current flowing through the

primary circuit, the ammeter shows no reading.

When the switch is opened, the ammeter needle

deflects to the left momentarily, then returns to 0.


Chapter 20 magnetic flux faraday s law

A

_

+

Faraday’s Conclusions:

Steady currentsin the primary produce constant magnetic fields, which result in no current in the secondary circuit.

Changing currents in the primary circuit result in changing magnetic fields, which result in induced currents in the secondary circuit.


Chapter 20 magnetic flux faraday s law

A

S

N

If we move a bar magnet toward a loop of

wire, the ammeter deflects to the left.

When we stop moving the magnet, the

ammeter reads 0.

When we pull the magnet away from the loop,

the ammeter deflects to the right.


Chapter 20 magnetic flux faraday s law

A

S

N

As the magnet moves toward the loop, the

magnetic field near the loop increases.

As the magnet moves away from the loop, the

magnetic field near the loop decreases.

Such results are consistent with Faraday’s

experiment: Changing magnetic fields lead

to induced currents.


Chapter 20 magnetic flux faraday s law

x x x x x

x x x x x

x x x x x

x x x x x

side view

A New Quantity

Magnetic

Flux

How much magnetic

field is passing through

the loop?

Huh?

One way to think about this is to simply count the number of magnetic field lines passing through a loop.


Chapter 20 magnetic flux faraday s law

x x x x x

x x x x x

x x x x x

x x x x x

30o

60o

side view

top view

Magnetic flux is the amount of magnetic field

perpendicular to the loop.

If you separate the magnetic field into

components parallel and perpendicular

to the loop, you see that...


Chapter 20 magnetic flux faraday s law

Btot

q

30o

60o

This is also the direction of the normal to the loop!

top view


Chapter 20 magnetic flux faraday s law

Units!

So, the Weber is the unit of magnetic flux.


Chapter 20 magnetic flux faraday s law

Concept Quiz!

B Flux


Chapter 20 magnetic flux faraday s law

?

What is the magnetic flux through a square loop of side length 10 cm whose normal is at an angle of 60o to the direction of a uniform magnetic field of strength 1 T?


Chapter 20 magnetic flux faraday s law

EMF!

Potential

Differences

What causes currents to flow?

Having defined the magnetic flux, we can

now quantify the induced EMF we have

seen in the secondary circuit.

N is the number of turns

Faraday's Law


Chapter 20 magnetic flux faraday s law

Concept Quiz!

Solenoids & Light Bulbs


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