lenz's law TBR example

[Oh_Gee]

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"Example 8.10b
A metal loop moving left to right across the following B field would induce a:
00000000
00000000
00000000

(the field is coming out of the screen)
A. clockwise current once it was fully immerse in the field.
B. counterclockwise current once it was fully immerse in the field.
C. clockwise current upon entry and a counterclockwise current upon exit.
D. counterclockwise current upon entry and a clockwise current upon exit.
Solution
An induced current only occurs upon entering or exiting the field, so choices A and B are eliminated. Upon entering the field from the left, the loop would experience a gain in dots, which would induce a clockwise current to generate Xs. The best answer is choice C."

so is it counter on entry because if you do the right hand rule, the force is pointing down? does lenz's law dumbed down mean that current flows in the direction of force?

 

[dnrs]

Use the right hand rule where you wrap your right hand around a wire with your thumb pointing in the direction of the current flow and the other fingers point in the direction of the magnetic field. Do not use the right hand rule where the force is involved. Lenz law states that the current in the wire will counter the change in the magnetic field. Since upon entry, the magnetic field increases out of the page, the current will create magnetic field into the page to counter it. Upon exit, the magnetic field decreases out of the page, the current will create magnetic field out of the page to compensate.

Hope this helps.

 

[Oh_Gee]

in this question, does the direction of velocity not change the direction of the current?

 

[dnrs]

I am not sure what you mean, but the direction of the flow of electrons is opposite the direction of the current.

The reason I say use the simple right hand rule because it tells you the direction of the magnetic field created by current in a wire.

The other right hand rule uses an external magnetic field and the current flow to give you the direction of the force, which is not related to this problem.

 

[Oh_Gee]

I am not sure what you mean, but the direction of the flow of electrons is opposite the direction of the current.

The reason I say use the simple right hand rule because it tells you the direction of the magnetic field created by current in a wire.

The other right hand rule uses an external magnetic field and the current flow to give you the direction of the force, which is not related to this problem.

by velocity, i was referring to how the question says the loop moves from left to right across the magnetic field

 

[Cawolf]

No, the direction that the loop moves into the field will not effect the answer.

All that matters is if the field is increasing or decreasing and the direction it points.

 

[Oh_Gee]

how does alternating and direct current work in this question?

 

[Cawolf]

That does not really apply to this question as there is no circuit.

It is an induced current that switches direction once, similar to mechanism of an alternator that would generate AC in a circuit.

I am not sure if this is technically AC, but I think for all intents and purposes it doesn't matter.

 

[Oh_Gee]

That does not really apply to this question as there is no circuit.

It is an induced current that switches direction once, similar to mechanism of an alternator that would generate AC in a circuit.

I am not sure if this is technically AC, but I think for all intents and purposes it doesn't matter.

oh i was just wondering because this question confused me

What is true of a conducting loop that spins within a magnetic field about an axis
perpendicular to the magnetic field?
A. It experiences an induced alternating current.
B. It experiences an induced direct current of constant magnitude.
C. It experiences an induced direct current of changing magnitude.
D. It experiences no current.
Solution
As the loop rotates about an axis that is perpendicular to the magnetic field, it
gains Xs(refers to the field pointing in) some of the time followed by a period of time where it loses Xs. This means that the current could be either counterclockwise or clockwise at different pointsin its revolution, so the current is alternating. Togenerate a direct current,
the loop would need to always be entering or always be exiting the field, which is physically impossible. Spinning loops in an external magnetic field generate induced, alternating currents.This is the principle behind electrical generators. The best answer is choice A.

if it were a conducting loop that didn't spin in the field, would it be direct current?

 

[Cawolf]

Which question is that?

It depends on how the field and loop look.

 

[IslandStyle808]

oh i was just wondering because this question confused me

What is true of a conducting loop that spins within a magnetic field about an axis
perpendicular to the magnetic field?
A. It experiences an induced alternating current.
B. It experiences an induced direct current of constant magnitude.
C. It experiences an induced direct current of changing magnitude.
D. It experiences no current.
Solution
As the loop rotates about an axis that is perpendicular to the magnetic field, it
gains Xs(refers to the field pointing in) some of the time followed by a period of time where it loses Xs. This means that the current could be either counterclockwise or clockwise at different pointsin its revolution, so the current is alternating. Togenerate a direct current,
the loop would need to always be entering or always be exiting the field, which is physically impossible. Spinning loops in an external magnetic field generate induced, alternating currents.This is the principle behind electrical generators. The best answer is choice A.

if it were a conducting loop that didn't spin in the field, would it be direct current?

I am really junk at explaining this, but here is an explanation of the concept from khan academy:

https://www.khanacademy.org/science/physics/electricity-and-magnetism/v/magnetism-9--electric-motors

They also explain it in more detail in videos 10 and 11.

 

[theyellowking]

For Lenz's law, you're only focusing on the RH rule dealing with current (I) and magnetic field. As someone previously mentioned, v and F really have no impact.

As your thumb sticks out (B) with your RH, your other fingers curl in a counterclockwise fashion, which is the direction of current.

"O" indicates the magnetic field going out towards you. The book compares Lenz's law to Le Chat's principle, which is pretty smart. As you enter the magnetic field of "O," Le Chat states that there will be an attempt to "decrease the amount of O's." In other words, you want to increase the amount of X's (Magnetic field pointing away from you). Using the RH rule I previously put up there, that would be clockwise.

When you leave the magnetic field, there will be an attempt to "increase" the amount of O's, and this will be counterclockwise direction of I.

I might have over explained this, but hopefully it helps.