Magnetic Induction

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# Magnetic Induction - PowerPoint PPT Presentation

Magnetic Induction. Transforming energy with magnetism. F = qv  B. Lorentz Force Reminder. Source : Griffith, The Physics of Everyday Phenomena. F is directed out of the screen. CPS Question. What is the direction of the Lorentz force on the charges moving in this wire?. B. A. D. B.

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### Magnetic Induction

Transforming energy with magnetism

F = qv  B

Lorentz Force Reminder

Source: Griffith, The Physics of Everyday Phenomena

Fis directed out of the screen.

CPS Question

What is the direction of the Lorentz force on the charges moving in this wire?

B

A.

D.

B.

E.

C.

F.

I

+

induced potential

Moving Creates a Potential

B

v

Motional emf
• Moving a conductor through a magnetic field causes separation of charges.
• Back-emf (motional emf) in conductor cancels potential from motion

e = lvB

• when l, v, B all orthogonal

a

b

c

d

e

Group Work
• At which position(s) does the most magnetic flux pass through the loop?
• At which position(s) does the magnetic flux through the loop change the fastest?

a

b

c

d

e

Group Work
• What is the current direction at these points?

a

b

c

d

e

• Greatest fluxF when perpendicular
• Fastest change in flux DF/Dt when parallel

Motion

V

through the field

v

V

induces a potential

v

B

Rotation Powers a Generator

which generates a current

that charges the battery

Group Work

Which direction is the flux change?

What current would oppose it?

What is the Lorentz force on each side?

If the magnetic field intensifies, in what direction will the induced current be?

B

How a Loudspeaker Works

loudspeaker

induced motion of magnet

current-generated field attracts or repels magnet

current

B

m

I

Back Potential
• As the motor turns, back-potentialDFB/Dt opposesm
• Faster rotation  more back potential