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Physics 1402A/B Lecture 9: Lecture 9 Notes - Motional Emf

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School
Western University
Department
Physics
Course
Physics 1402A/B
Professor
Jan Cami

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Document Summary

By the end of this lecture you should be able to explain how lenz"s law results in magnetic breaking through the generation of eddy currents. Recall faraday"s law which states that the emf (voltage) induced in a circuit is. Recall lenz"s law which analyses the directionality of the direction of an induced current based on the effects it has in respect to the magnetic field it generates. "the direction of an induced current is such that the magnetic field (and thus flux) generated by that induced current opposes the change in magnetic flux that created the induced current. " If the rail is already moving, when we apply the perpendicular magnetic field, the area of the loop enclosed would change. Flux will change for this conducting loop and faraday"s. Law says that this will induce an emf in the circuit. Extrapolating, we can get a motional emf whenever a conductor moves through a field.

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Related textbook solutions

Physics: Principles with Applications
7th Edition, 2013
Giancoli
ISBN: 9780321625922

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Related Questions

1. Lenz's law states that the induced current and induced emf in a conductor is in such a direction as to enhance the magnetic flux change that produced them. T/F
2. The magnitude flux through a surface depends on the magnitudes of the magnetic field and surface area only. T/F
3. Like a sound wave, propagation of EM waves requires air as a medium. T/F

A loop of wire is lying flat on a tabletop. A uniform magneticfield is directed vertically UPWARDS such that it is perpendicularto the tabletop (and the loop) and pointing toward the ceiling.Beyond the edges of the table, the magnetic field is zero. Imaginethat you are looking DOWN on the loop from above. Which of thefollowing statements are true about the induced EMF in the wireloop?

1)If the magnetic field suddenly decreases, the induced currentwill be in a counter-clockwise direction.
2)If the magnetic field suddenly decreases, the induced currentwill be in a clockwise direction.
3)If the loop suddenly shrinks in size, the induced current will bein a clockwise direction.
4)If you pull the loop out of the field, by sliding it off thetable, the induced current will be in a clockwise direction.
5)Lenz's Law states that the induced current always leads to amagnetic field that OPPOSES the change in magnetic flux.
6)If you keep the loop on the table, but pull it to the right,there will be no induced current.

1a) Faraday discovered that a current is induced in a coil

A) only when the N pole of a magnet is inside the coil
B) only when the S pole of a magnet is inside the coil
C) only when there is a magnetic field inside the coil
D) only when the magnetic field inside the coil is changing

1b). A conductor moves through a uniform magnetic field at speed v and has a motional emf V created across it. If the conductor were to move twice as fast through the magnetic field, the motional emf would be:

A) V
B) 2V
C) 4V
D) V/2
E) V/4

1c) In the conducting rail discussed in section 25.2 (where the rail is moving at constant speed), what can you say about the power input due to the person pulling on the rail and the power dissipated in the resistance?

A) Power input from pull = power dissipated in R
B) Power input from pull > power dissipated in R
C) Power input from pull < power dissipated in R

1d) The electric generator as shown in the reading generates electricity by:

A) rotating a loop inside a magnetic field
B) moving a magnet in and out of a loop
C) sliding a loop over a magnet
D) running current through a loop in a magnetic field

1e) The magnetic flux through a loop:

A) is proportional to the number of magnetic field lines going through it
B) depends just on the B field going through the loop
C) is maximized when the B field lines in the plane of the loop
D) is zero when the B field is perpendicular to the plane of the loop
E) doesn't depend on the direction of the B field

1f) According to Lenz's Law, the induced B field (due to the induced current) will:

A) be in the opposite direction of the existing B field
B) be in the same direction as the existing B field
C) be in the same direction as the change in the existing B field
D) be in the opposite direction of the change in the existing B field

1g) A stationary coil experiences a doubling of its magnetic field (no change in direction of the field) in a time T and has a given induced EMF. If the same change were to have happened in half the time (T/2), the induced EMF would have been:

A) half as large
B) the same
C) twice as large
D) one-fourth as large
E) four times as large

1h) Eddy currents:

A) make it hard to pull a nonmagnetic material through a magnetic field
B) make it hard to pull a magnetic material through a magnetic field
C) speed up a magnetic material moving through a magnetic field
D) speed up a nonmagnetic material moving through a magnetic field